PFC/RR-85-12
DOE/ET-51013-155
UC20b
MIT 12 TESLA COIL TEST RESULTS
Steeves, M.M.; Hoenig, M.O.
July 1985
Plasma Fusion Center
Massachusetts Institute of Technology
Cambridge, Massachusetts 02139 USA
i
MIT 12 TESLA COIL TEST RESULTS
BY
M.M. Steeves and M.O. Hoenig
MIT Plasma Fusion Center
ABSTRACT
Test results from the MIT 12 Tesla Coil experiment are presented. The coil was tested
in the High Field Test Facility (HFTF) of the Lawrence Livermore National Laboratory
in October 1984 and January 1985. The experiment measured the performance of an
Internally Cooled, Cabled Superconductor (ICCS) of practical size, intended for use in
magnetic fusion experiments. The MIT coil carried 15 kA at 11 T for 5 minutes with no
sign of instability. A half turn length in a 10 T field was able to absorb a heat load in 4
msec of more than 200 mJ/cm 3 of cable volume while carrying a current of 12 kA. The
MIT coil successfully met the performance requirements of the Department of Energy's 12
Tesla Coil Program.
ii
P
P.-
CONTENTS
page
1.0 Introduction ......................................................................
1
2.0 R esults ...........................................................................
2
2.1 Critical Current At 4.2 K ....................................................
2
2.2 Steady State Operation ......................................................
4
2.3 Critical Currents Above 4.2 K ................................................
4
2.4 Lap Joint Resistances ........................................................
4
2.5 Transient Stability ...........................................................
6
2.6 Q uench ......................................................................
6
2.7 Q uench Pressure .............................................................
6
3.0 C onclusions ......................................................................
8
3.1 Steady State Stability Requirement ...........................................
8
3.2 Transient Stability Requirement ..............................................
8
4.0 D iscussion ........................................................................
9
5.0 R eferences .......................................................................
10
6.0 A ppendix 1 - Test Plan ..........................................................
11
7.0 Appendix 2 - Interface Specification.....................................95
8.0 Appendix 3 - Operation of the HFTF..................................
111
1.0 INTRODUCTION
The MIT 12 Tesla Coil was built to test the performance of an Internally Cooled,
Cabled Superconductor (ICCS) of practical size. The type of cable-in-conduit conductor
investigated is identical to the Westinghouse Large Coil Program conductor and is intended
for future use in high magnetic field fusion experiments. It consists of a 486 strand cable
of Oxford-Airco bronze-matrix, multifilamentary Nb 3 Sn enclosed in a conduit of JBK-75
superalloy. The test coil contains approximately 120 m of this conductor in the form of
three double pancakes. The double pancakes are connected by means of resistive copper
lap joints. Fabrication of the coil took place at Everson Electric Company of Allentown,
Pennsylvania under MIT supervision.
The coil was tested in the High Field Test Facility (HFTF) of Lawrence Livermore
National Laboratory in October 1984 and January 1985. It successfully met the requirements defined by the Department of Energy at the outset of the 12 Tesla Program in 1979.
Further details of the conductor and coil are listed in Appendix 1 and the References.
1
2.0 RESULTS
Results of the MIT 12 Tesla Coil experiment are summarized below.
2.1 Critical Current At 4.2K
The critical current at 4.2 K of the crossover turn of the central double pancake,
called subcoil B, is shown in Figure 1. The length of the crossover turn conductor in high
field, used to determine the critical current, was approximately 130 cm. The maximum
critical currents measured are shown by the solid circles on the two coil load lines, defined
to be curves relating the maximum field at the conductor to its current. These maximum
currents were not due to limitations of the conductor. Rather, they were determined by
the limitations of the available power supply and by the conservatism of the experimenters.
The background magnetic field, due to the six High Field Test Facility magnets, is
shown at the intersection of each coil load line with the horizontal axis. The maximum
available background field at the crossover turn of subcoil B was 8.93T. The other background field, 8.38 T, was selected arbitrarily.
The critical currents, given as lines that intersect the load lines, are shown at four
sensitivities: 0.01, 0.015, 0.03, and 0.11 gv/cm. The most accurate data is at the highest
average electric field, that is, at 0.11 uv/cm. Note that data along the load line starting
at 8.93 T was measured at 10 times the sensitivity as that along the load line starting at
8.38 T. Thus, there was approximately.10 times the uncertainty in the determination of
critical currents along the 8.38 T load line. For this reason, the lines of critical current at
sensitivities below 0.11 v/cm have been drawn parallel to that at 0.11 v/cm, starting
at points on the 8.93 T load line.
Data were taken at zero helium mass flow and two internal helium pressures: 1 and
3 atmospheres absolute. As shown in the figure, the critical current at 4.2 K is 16,900
amperes at 11.7 T and an average electric field of 0.11 uv/cm.
Cal
II
.. .. ... ..
011
I
I
_
-I*
::1
F-
-
-(
-
-
-ia-t
r-
-t.
.
. . .
Fig. 1. Critical current of the MIT 12 Tesla Coil at 4.2 K. Coil load lines start at HFTF
background fields of 8.38 and 8.93 T. Data were taken with no helium flow at internal absolute pressures of 1 and 3 atm. Maximum critical currents are given at a
measurement sensitivity of 0.11pv/cm.
3
2.2 Steady State Operation
The coil was held at 15 kA, 10.85 T for 300 s with internal helium at 1 atmosphere
absolute pressure, 4.2K and no flow. During this test, the average electric field along the
crossover turn of Subcoil B was approximately 0.013 v/cm. The power per unit length
dissipated in the crossover turn was therefore approximately 200 pw/cm. Note that since
the internal helium was at 1 atmosphere, steady state stability was enhanced somewhat
by the available heat of vaporization. This would not have been the case had the internal
helium been supercritical (above 2.26 atm at 4.2 K).
2.3 Critical Currents Above 4.2 K
Four measurements of subcoil B critical current were made at elevated tmperatures:
two at approximately 5.2 K, and two at approximately 7.5 K. These critical currents are
shown in figure 2 as points 1-4, at a sensitivity of 0.015 v/cm. During this portion of the
experiment, internal helium pressure was held at 3 atm absolute, and there was no helium
mass flow through the subcoil. The uncertainty in helium temperatures was approximately
0.2 K. Note that point 5, taken from figure 1, is a 4.2 K point shown for reference.
2.4 Lap Joint Resistances
Termination lap joint resistances at the coil leads and joints were measured with the
HFTF background magnetic field both off and on. All lap joint resistances appeared to
be independent of current in both cases. The average magnetic field at the leads and
joints when the HFTF was energized was approximately 1.5 T. Lap joint resistances were
higher, on the average, when the background magnetic was energized. Note that the
largest measured resistance, 74 nfl, was nearly one order of magnitude larger than the
value estimated by design calculations. Lap joint resistances are summarized in Table 1
below.
Table 1. MIT 12 Tesla Coil Lap Joint Resistances
Location
HFTF Off
HFTF On
A Lead
C Lead
A-B Joint
B-C Joint
25nfl
9nf
53ni
13nfl
33nfl
9n11
74nfl
16nn
4
-
7
1:::
-
--
~
.
7
"
-
--
T
-
-
- - -
-- -
~
::
-
- --
--
-
-
-
- -
v.
-
-
-
-
-
--
....
~j
...
-
-
11,
-
±
-
-
--5
i1 i--i----V~ti
-
-
----
--
~
4
-
i
.
-T
3.
--
--
-(
Fig. 2. Elevated temperature critical currents of the MIT 12 Tesla Coil. Measurements were
taken at 5.2 and 7.5 K at an internal absolute pressure of 3 atm with no helium flow.
Data are shown at a measurement sensitivity of 0.015 Av/cm.
5
I
2.5 Transient Stability
The ICCS transient heat load stability was verified to be in excess of 200 mJ/cm3
of cable volume when operating at 10 T, 4.2K, 3 atm helium pressure, zero flow and a
steady state current of 12,000 A. Energy was delivered by an. inductive heating technique
that used a pulse coil as a transformer primary and the ICCS as a transformer secondary.
The current pulse into the pulse coil had a waveshape that was a quarter sine wave with
a duration of approximately 4 ms.
The stability test involved one 4100 ampere current pulse from a 87,000 1tF capacitor
bank, charged to 250 V, into the pulse coil of subcoil A. The intended wave shape was
a half sine wave. Unfortunately, the pulse coil leads were inadequately supported and
broke at the peak of the current pulse, causing the current to collapse in less than one
millisecond. This truncated the pulse into a quarter sine wave.
Previous work had shown that a half sine wave current pulse of 4100 A and 8 ms
duration would deliver more than 200 mJ/cm3 to the cable under the operating conditions
described above. Because the intended half sine wave was truncated into a quarter sine
wave, the rapid collapse of current resulted in a higher energy input than expected. This
led to the conclusion that the energy delivered was greater than 200 mJ/cm 3 .
2.6 Quench
The crossover turn of subcoil B, operating at 7.5 K temperature, 3 atm helium pressure
and zero helium flow was purposely driven normal at 9.5 T by ramping the current to
15,200 A. The resulting quench was followed by a safe discharge of the coil current using
the power supply diode rather than the dump resistor. None of the HFTF background coils
were adversely affected by the discharge of the MIT coil and did not have to be dumped.
2.7 Quench Pressure
Helium pressure at one end of subcoil B is shown as a function of time in Figure .3
for the quench of the MIT 12 T Coil. Coil current as a function of time is also plotted.
The initial conditions were stated in Paragraph 2.6. The boundary conditions were open
stainless steel pipes of 1.1 cm inner diameter. Pressure was measured at approximately 71
cm from the connection of the pipes to the conductor. The end pressures rose from 3 atm
to approximately 4 atm as a result of the quench.
6
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I
3.0 CONCLUSIONS
The MIT Coil satisfied the major requirements of the 12 Tesla Program.
3.1 Steady State Stability Requirement
This program requirement stated that candidate test coils must carry between 10 and
15 kA in a maximum magnetic field of 11-12 Tesla. The MIT coil satisfied the steady state
stability requirement. It was tested at 15,000 A and 11 T for 5 minutes and showed no
signs of instability.
3.2 Transient Stability Requirement
This program requirement stated that candidate test coils must not quench when
subjected to a transient heat load of 100 mJ/cm 3 over a half turn length in the high field
region, with the time of energy deposition not exceeding 50 msec. As mentioned above,
conductor stability was verified to be above 200 mJ/cm 3 at 10 T for a 4 msec heat pulse.
8
4.0 DISCUSSION
The MIT 12 Tesla Coil experiment demonstrated that an ICCS of practical size works
well in a realistic coil environment. The conductor met the steady state and transient
stability requirements stated at the program inception in 1979. The major objectives of
the program were thus satisfied.
However, the opportunity to thoroughly study the stability of a full size ICCS was
lost. The pulse coil inductive heater leads were inadequately supported and failed when the
capacitor bank was discharged. Although more than enough energy was delivered to the
ICCS to satisfy the transient stability requirement, the lead failure brought an immediate
halt to stability testing.
Had the leads not failed, stability testing would have been limited by two other considerations. First, the energy delivered by the pulse coil power supply did not cover a
large enough range of fields and currents at 4.2 K. Although data for ratios of transportto-critical current near 1.0 could have been obtained, this would have been an incomplete
set. Second, and perhaps more economically important, the heat load on the HFTF dewar
was larger than the available refrigeration capacity. This meant that liquid level could be
maintained only by using liquid from external storage dewars. The helium recovery system
was not sized to capture all the boiloff from the experiment, resulting in substantial helium losses to the atmosphere. Stability testing was begun when the storage dewars were
perhaps 30% full. At best, the available liquid helium would have permitted several hours
of stability testing.- Had the test been able to continue, it would have been necessary to
purchase at least another 4000 liters of liquid helium.
Note that none of the reasons cited above preclude future stability testing of the MIT
12 Tesla Coil. For example, the pulse coil leads can be brazed back together, wet-wrapped
with fiberglass tape and epoxy, and then perhaps placed inside stainless steel tubes for
support. To repeat, the pulse coil leads are repairable.
The amount of delivered energy could be increased in the future by using a double
current pulse, a technique that requires two separate capacitor banks. These banks and
associated electronics now exist at MIT and have been used many times in similar stability
experiments.
Efforts have been made to upgrade the refrigeration capacity of the HFTF. Future
testing should no longer be determined by the storage capacity of external dewars. If
interest in stability testing of the MIT 12 Tesla Coil revives, then the HFTF may be
operational for extended periods of time.
In summary, the MIT 12 Tesla
outlined in 1979. However, the MIT
information about ICCS conductor
arise, the experiment can be revived
Coil experiment satisfied the program requirements
12 Tesla Coil still has the potential to provide useful
stability to the fusion community. Should the need
with relatively modest effort.
9
5.0 REFERENCES
1. Hoenig, M.O., et al.,"Progress in the ICCS-HFTF 12 Tesla Coil Program," IEEE
Trans. on Magnetics, Vol. Mag-17, No.1, p.638, Jan. 1981.
2. Hoenig, M.O., et al.,"Cryogenic Aspects of the Internally Cooled, Cabled Superconductor (ICCS) for the 12 Tesla Program," Adv. in Cryo. Eng., Vol. 27, p.217, 1982.
3. Steeves, M.M. and Hoenig, M.O., "Lap Joint Resistance of Nb 3 Sn Cable Terminations
for the ICCS-HFTF 12 Tesla Coil Program," IEEE Trans. on Magnetics, Vol. Mag-19,
No.3, p.378, May 1983.
4. Hoenig, M.O. and Steeves, M.M., "MIT 12 Tesla Test Coil Experiment," IEEE Trans.
on Magnetics, Vol. Mag-21, No.2, p.1052, March 1985.
10
6.0 APPENDIX 1 - TEST PLAN
. The test plan for the MIT 12 Tesla Coil is presented here as an archival document. It
covers the intended steps of the experiment from the room temperature check of the helium
supply system to final stability tests with an AC ripple superimposed on the transport
current. It also gives information about the conductor, coil, helium supply system and
instrumentation used in the experiment.
TABLE OF CONTENTS
PAGE
1.0
INTRODUCTION ..................................................
2.0
TEST PLAN ......
............
.
1
.........
.
.... .
..
.........
.
2
2. 1
Room Temperature Check of Helium Supply System ..........
2
2. 2
Room Temperature Check of Instrumentation .........
2
2.
Cool-down to 4.2 K ......
3
3
Zero Background Field - Flow, Pressure and Ter-
2. 4
2. 5
2. 6
2. 7
2. 8
perature Calibrations .............
. ... ....
.0...
... .....
Zero Background Field - 12 T Coil Terminations Tests ...
Zero Background Field - Heating Tests ...................
Zero Background Field - Protection Circuit Test
.....
3
3
5
10
Calibration of Pressure Transducers and CGR's in
Background Magnetic Field ..........
.
.........
Critical Current Tests .............
..................
2.10 Transient Stability
Tests .......................
2.10.1
Zero Flow, 2.5 atm, 4.2 K and 10 T ..................
2.10.2
Zero Flow, 4.2 K, 10 T and 1-10 atm .................
2.10.3
Mass Flow, 4.2 K, 2.5 atm and 10 T .................
..
..
10
10
14
14
16
17
2. 9
.....
2.10.4 Zero Flow, 2.5 atm, 10 T and T > 4.2 K ............
2.11
Critical Temperature Tests .............................
2.12
2.13
Steady-State Current Sharing Tests ...................
Quench Propagation and Helium Expulsion Tests ...
...
2.14
AC
Ripple Tests ........................................
APPENDIX 1 -
Conductor and Coil Parameters
APPENDIX 2 -
Helium Supply System ..................
APPENDIX 3 -
Instrumentation
. ........
APPENDIX 4 - Termination Lap Joints
APPENDIX
............
5 - Transient Stability Model
12
28
.30
35
......................
...
.
19
23
23
23
.....
41
..............
56
......................
60
-
" - ,,
-I-
TEST PLAN - MIT ICCS 12 TESLA COIL
1.0
INTRODUCTION
The MIT ICCS 12 Tesla Coil has been built to test the performance
of an Internally Cooled, Cabled Superconductor (ICCS) of practical size.
This cable-in-conduit conductor is similar to the Westinghouse LCP conductor and is intended for use in fusion experiments such as the proposed
It consists of a 486 strand cable of Airco bronze matrix
Alcator DCT.
The
multifilamentary Nb 3 Sn enclosed in a conduit of JBK-75 superalloy.
of
the
the
form
conductor
in
120
m
of
contains
approximately
test coil
connectare
subcoils,
called
double
pancakes,
The
pancakes.
three double
ed by means of resistive copper lap joints. Details of the conductor and
coil are listed in Appendix 1.
13
7
-2-
2.0
TEST PLAN
2.1
Room Temperature Check of Helium Supply System
2.1.1
Description
Appendix 2 gives a detailed description of the helium supply
system for the 12 Tesla Coil.
Briefly, it consiists of a room temperature helium source capable of supplying up to 9 g/s at a maximum
inlet pressure of 100 psig. The inlet helium travels through an external liquid nitrogen heat exchanger before entering the helium
flow assembly built by MIT.
The assembly contains counterflow and
liquid helium heat exchangers and has hand operated cryogenic valves
in the flow circuit of subcoil B.
2.1.2
Helium Purge and Leak Check
The helium flow assembly will be leak tight per helium mass
spectrometer leak tests upon departure from MIT.
At Livermore,
piping subassemblies containing transducers will be welded or brazed
V~ C U.ALw
-s
/
I-
/~
I-
to the
12 Test Coil helium piping.
On completion,
the entire
cool-
ing system will be pumped down to vacuum and then purged with helium.
The system will then be pressurized to 100 psig and pressure decay
monitored for at least
a 2 day period.
This test
will be implemented
by helium mass spectrometer leak testing, if necessary.
Leaks will
be patched by welding or brazing.
While undergoing vacuum pumpout
and purge, the system shall be heated, if possible, by heat lamps.
2.1.3
Valve Check
All valves will be checked out at this time.
After check
out, all
hand operated valves except cryogenic valve VC1 shall be
left closed.
VC1 shall be left
open.
See Appendix 2.
2.2
Room Temperature Check of Instrumentation
2.2.1
Description
Instrumentation sensors and heaters
are detailed
in Appendix
2.
Briefly, the 12 Tesla Coil has voltage taps, pulse heating coils,
pulse pick up coils, a heater wire in subcoil B, carbon glass resistor thermometers, pressure transducers and a Hall probe.
14
-3-
2.2.2
Continuity Tests
The voltage taps, pulse heating coils, pulse pick coils,
heater wire shall be tested for continuity.
2.2.3
and
Excitation Tests
The carbon glass resistors, pressure transducers and Hall
probe shall be excited according to their individual specifications.
Output signals will be measured while individual sensors are under
excitation.
2.3
Cooldown to 4.2 K
When the coil assembly is positioned in the HFTF 2 meter diameter
hand operated valves ascryostat, and cooldown is about to begin, all
sociated with the helium supply system shall remain closed except cryWhen cooldown begins, inlet valve VR1 will be opened
ogenic valve VC1.
This allows
and the inlet pressure set at 22 psig (2.5 atm absolute).
helium to condense in the 12 Tesla Coil as the entire assembly cools to
2.4
Zero Background Field
begin.
-
d-
Flow, Pressure, and Temperature Calibrations
Assuming no cold leaks, zero background magnetic field testing will
The first
test will be to establish the mass flow capability of
the blnq.-doni
nystem
through
mubcol
!hun
T
B
valv.R
Vil4--rnd-
TT4
are
-
condition of 2.5 atmospheres at zero mass flow.
opened from an initial
Maximum mass flow available will be established by increasing the inlet
pressure to its peak value and reading mass flow on SAroob tetperature
Flow will also be mesured on venturi meter
flow meter, apstree.-.FV4.
VM2.
LTh(,
VS e
Once'mass flow capabilities are established at 2.5 atm, recovery
presThen all
will be closed, returning mass flow to zero.
valve
sure transducers and CGR's will be excited and their outputs recorded.
Pressure will then be raised in steps to 100 psig, allowing inlet flow to
drop to zero after each step, to calibrate the pressure transducers in zero
magnetic field.
2.5
Zero Background Field -
12 Tesla Coil Terminations Tests
With the HFTF solenoids at zero current, the 12 Tesla Coil will be
condiThe initial
energized in steps of 5,10,14,16,17,18,19 and 20 kA.
tion will be zero mass flow at 2.5 atm pressure with valve# VB- and VB5
Voltage drops across the two lap joints between subcoils and
closed.
across the coil leads will be monitored to check the performance of the
coil terminations and joints.
15
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1.
-Lag
oldC-- L
Termination lap joint voltage drop tests at zero background
magnetic field.
19
-5-
The expected voltage drop across
than 100 pV, resulting in a total heat
joint. Details of the lap joints are
volt-ampere characteristic of the lap
is shown in Fig. 2.
The zero field
each lap joint at 20,000 A is less
load of not more than 2 watts per
given in Appendix 4.
The expected
joints in a 1 Tesla magnetic field
curve should lie below this line.
The termination lap joint tests provide a convenient opportunity to
check the 12 Tesla Coil load line, since a Hall probe is installed in the
coil case near the high field point. The 12 Tesla Coil is expected to proa .
duce 1.77 G/A.
At 20,000
A,
the maximum
i [T
4--7x 10
B
output
of the
12 Tesla
(1)
-
Coil power
supply,
the
expected self field will be 3.54 Tesla , as shown in Fig. 3.
2.6
Zero Background Field - Heating Tests
Tests of the heater wire in subcoil B and the three crossover turn
pulse coils will take place after completion of the termination lap joint
tests. The initial condition will be zero mass flow at 2.5 atm and 4.2 K
as in previous tests.
Depending on the voltage and power output of the available heater
wire power supply, the heater will be supplied with currents ranging from
0.2 to 2 amperes.
These currents will produce steady-state temperatures
ranging from 4.5 to more than 20 degrees kelvin as shown in Fig. 4.
The
heater will
be energized in steps of 0.2 A according to the schedule of
Table 1.
Thermal equilibrium should be reached in approximately 3 to 5
minutes at each current level.
Steady-state temperatures will be measured by carbon glass resistors
stationed at the 900 and 2700 positions on the crossover turn of subcoil B.
It is estimated that these thermometers will read within 5% of the helium
temperature, and therefore within 5% of the superconductor temperature.
After the highest equilibrium temperature is recorded, subcoil B will be
flushed at approximately 1 gram/second and the time to return to 4.2 K
will be recorded.
20
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Figure
2.
The
Estimated A-B and B-C lap joint voltage drops at 4.2 K.
I
of
field
magnetic
average
an
in
joints are assumed to be
Tenla.
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23
-9-
TABLE 1.
Subcoil B Heater Wire Test at Zero
Field and Zero Flow
Vheater
OV
24
48
72
96
120
144
168
iheater
OA
.2
.4
.6
.8
1.0
Current,
Zero Magnetic
ESTIMATED
STEADY-STATE T
4.2 K
4.5
5.3
6.7
8.6
2"
=Z
AA
-
11.2
14.3
17.9
1.2
1.4
Rh =
134 a (4.2
K)
Upon completion of the heater wire tests, the three pulse coils will
be fired. starting with pulse coil B.
The initial
condition will be zero
flow at 2.5 atm and 4.2 K. Prior to firing, the series resistance of the
power supply leads and pulse coil will be measured.
Pulse coil B will
then be fired in steps of 100 volts according to the schedule of Table 2.
Temperatures at the 900 and 2700 positions will be monitored during the
sequence of discharges.
Voltages from the pulse pick-up coil will also
be recorded.
TABLE 2.
Subcoil B Pulse Coil Test
Field and Zero Flow
at Zero Current,
BVcap
PEAK
Ishunt
0V
100
200
300
400
OA
2,100
4,200
6,300
8,400
--tO50
._50
V
Zero Magnetic
0
I3-0
OV
4.5
9
13.5
18
22.5
R-k -(
24
Cc \
-10-
2.7
Zero Background Field - Protection Circuit Test
The 12 Tesla Coil will be protected by a 2l
dump resistor.
cuit will be interrupted by a single-pole circuit breaker.
20 V _
2Q
The cir-
12 T coil
With the coil at zero flow and 4.2 K and the background field at zero,
the coil will be charged to 5,000 amperes and interrupted by the circuit
breaker to test
the protection system.
The protection circuit
be repeated at higher currents if deemed necessary.
2.8
test
will
Calibration of Pressure Transducers and CGR's in Background Magnetic
Field
Critical current tests of the 12 Tesla Coil will start by first
energizing the HFTF background field coils.
These coils will be energized
in steps of approximately 1 Tesla with pauses between steps to record the
outputs of the pressure transducers, CGR's and Hall probe.
The initial
condition will be zero mass flow at 2.5 atm. Figure 5 shows the response
of CEC-1000 pressure transducers in magnetic field.
Figure 6 shows the
apparent thermal error of a typical CGR in magnetic
0 to 12 T.
2.9
fields
ranging
from
Critical Current Tests
Once the peak field at the 12 Tesla Coil midplane reaches 8 T, critiThe initial
condition will be supercritical current testing can begin.
Current will be slowly
cal helium at 4.2 K, 2.5 atm and zero mass flow.
ramped until the voltage drop across the crossover turn of subcoil B
(point of highest magnetic field) reaches 2pv (0.015pV/cm). Cukrent will
then be slowly ramped until the voltage drop reaches 20pV (0.151iV/cm), and
then cautiously ramped to 200iiV (1.5pjV/cm), the Airco electric field criSimilar critical current tests will be conductterion of the cable wire.
Figure 7 gives
ed with background fields of 7 T and-, if permissible, 9 T.
estimated critical current characteristics of the 12 Tesla Coil.
EI
VI_/c'V..,
0 0-.
A5V_
/
25
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2-8T
c
1.5
E
CEC
B-
1.0
OT
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NA
T
~7
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0.51
~-'3-
T= 4.2K
0
I
-0.5
0
100
50
150
P (PSIG)
RESPONSE OF TWO PRESSURE
TRANSDUCERS IN MAGNETIC
FIFI DS OF 0-8 T AT 4.2 K
27
200
Vi~
l~
~.
5
-12-
0.3
.I
-
ul
0.2
I
I
I
I
I
I
I
CARBON GLASS RESISTOR
LAKESHORE CRYOTRONICS
4.2KK
--
Ai k
7
LU
0
0.1
LUJ
Ii
0
1-i
0
Fi .6G
2
8 .9i
MAGNETIC FIELD (T)
4
6
I
10
APPARENT THERMAL ERROR DUE TO
APPLIED MAGNETIC FIELD
28
12
SA.A4EtA&-P
-13-.--
-
-
--
-
4
-4
d
0
0
g
0
z
U.
4.1
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til HE tt -_
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So
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a.
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g
= B
+ .7
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S
z
.
g
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-A
a
z
0
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0
S
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U
U
z
'.4
4,
z
0
C
CI
kp
!!_rf
,
I
1
-,,
N
U'
0
z
Figure
R
7.
Estimated critical current characteristics of 12 Tesla Coil at
three electric field criteria.
The maximum available background field is 9 T.
The maximum available power supply
currernt is 20 kA.
. 2T c.
.
vT-r-
E,- .- 015I~l /4g\c:-A
V
29
-14-
2.10
Transient Stability Tests
Upon completion of the critical current tests, transient stability
tests will begin. The HFTF solenoids will be charged so that the peak
field at the 12 Tesla Coil reaches some preassigned value.
Then the 12
Tesla Coil current will be raised to an appropriate fraction of critical
current to begin testing.
Testing will focus on subcoil B.
After the
capacitor bank has been discharged into pulse coil B, -the voltage versus
time plot is expected to behave in one of the following ways:
(1)
No voltage is observed across the crossover turn.
(Imposed energy is less than the critical energy).
(2)
Voltage appears, recedes to zero, and remains at
zero for more than 20 seconds. (Imposed energy
is less than the critical energy.)
(3)
Voltage appears, recedes to zero, then reappears
after 2 or 3 seconds. (Imposed energy is less
than the critical energy. Heat diffusion from
the pulse coil has caused quench.)
(4)
Voltage appears, recedes to zero or near zero,
then starts increasing.
(Imposed energy
equals the critical energy.
of interest).
(5)
This is the case
Voltage appears and remains above zero for 0.1
to 1.0 seconds.
(Imposed energy exceeds the
critical energy.)
The idea behind transient stability testing is to measure the energy
margin of the conductor.
Energy margin is defined as the maximum imposed
energy from which the conductor will recover.
This type of testing is
somewhat complicated by the poor cooling of the pulse coil, since heat
diffusion from the pulse coil can possibly lead to a superconductor quench.
The range of expected outcomes tabulated above reflects the possibility
Figure 8
of an unwanted quench due to heat diffusion (outcome No. 4).
plots estimated energy delivered to the cable as a function of initial
capacitor voltage (See Appendix 5).
2.10.1
Zero Flow, 2.5 Atmospheres, 4.2 K and 10 Tesla
condition will be zero mass flow at 2.5 atmoThe initial
a possible scenario for stability
Table 3 lists
sheres and 4.2 K.
These tests are relevant to the proposed
tests at 10 Tesla .
Alcator DCT.
30
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Figure
8.
.........
-------
--
Estinated energy per unit volume of cable vire delivered to
10 Teala
capacitor voltage at
cable as a function of initial
and 4.2 K.
...............
...........
ill I IIll Li U-SuIllub"11
..... ..... .....
.....
.....
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..........
31
.. ............
- -----------
-16-
Proposed Transient Stability Tests at Zero Flow, 2.5 AtmoWith I/Ic as the Independent
spheres, 4.2 K and 10 Tela
Variable (Ic a 24,000 A at 1.5 VV/cm).
TABLE 3.
CASE
NO.
ICOIL
BHFF
I
BTOT
-
-
Ic
9 T
I
2
8.5
EXPECTED
UV
(1.5 -)
ESTIMATED
Q
Vcap
cm
5,600 A
10 T
0.23
550 V
1750 mJ/cc
8,500
10
0.35
Soo
14SO
H4D
3
8
11,300
10
0.47
4
7.5
14,100
10
0.59
5
7
16,900
10
0.71
6
6.5
19,800
10
0.82
-
i
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T
7
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=4-
1
4-
ci>o
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i
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Fig Lre
9.
t
-4 41
Energy margin versus
j
4
IC for the tests defined 'in Tkble 3.
32
-
r - -- - --
-- -- -
------------- r
EL
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cl-i 11
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2.10.2
Zero Flow,
4.2 K,
and 1-10 Atmospheres
10 Tesla
This set of tests varies the helium pressure from subcritical at approximately 1 atmosphere to supercritical at 10 atmoproposed
Table 4 lists
spheres while holding I/IC and B constant.
tests with pressure as the independent variable.
Proposed Transient Stability Tests at Zero Flow, 4.2 K, 10
Tesla and I/IC M 0.6 With Pressure as the Independent
Variable.
TABLE 4.
CASE
NO.
7
8
BHFTF
P
5 atm
10
ICOIL
BTOTAL
10 T
7.5 T
14, 100 A
7.5
14,100
10
9
2
7.5
14,100
10
10
1
7.5
14,100
10
C-~-iv~1
EXPECTED
ESTIMATED
Vcap
9
S
'3ioV'
14,ov
14 u
0.
igure 10.
Energy mgrin versus pressure for tests defined
36
in' Table 4.
c.
/cc
-18-
2.10.3
Mass Flow, 4.2 K, 2.5 Atmospheres and 10 T
This set of tests is similar to those in paragraph 2.10.1
except the effects of mass flow will be studied.
The expectation
is that energy margin will be independent of mass flow.
Table 5
outlines the proposed energy margin tests.
Figure 11 illustrates
the expected dependency on mass flow.
TABLE 5.
CASE
m
Proposed Transient Stability Tests at 2.5 Atmospheres, 4.2 K,
10 T and I/Ic
- 0.6 With Mass Flow as the Independent Variable.
BHFTF
ICOIL
BTOTAL
EXPECTED
NO.
ESTIMATED
Vcap
11
1 g/s
7.5 T
14,100 A
10 T
12
2
7.5
14,100
10
13
3
7.5
14,100
10
14
4
7.5
14,100
10
15
5
7.5
14,100
10
Figure 11.
Energy
margin
versus 1
for
tests
defined
9
in
Table
5.
-19-
2.10.4
Zero Flow, 2.5 Atmospheres, 10 T and T > 4.2 K
In this set of tests the helium temperature will be raised
in steps above 4.2 K until the energy margin of the conductor reaches
zero. Helium temperature will be controlled via the heater wire in
Figure 12
Table 6 outlines the proposed set of tests.
subcoil B.
Figure 13 plots expected nonillustrates the expected behavior.
copper critical current density as a function of temperature. Figure 14 is essentially the same plot with critical current plotted as
a function of temperature.
TABLE 6.
CASE
Proposed Transient Stability Tests at Zero Flow, 2.5
Atmospheres, 10 Tesla -and Ic - 2_4,100 A With Temperature as the Independent Variable.
T
BHFTF
BTOTAL
NO.
MV
I
-
(1.5 -)
-4.5
12
~5
13
5.5
14
_15
K
~6
_
6.5
ESTIMATED
VcapQ
cm
Ic
11
EXPECTED
7.5 T
10 T
.62
7.5
10
.68
7.5
10
.76
7.5
10
.86
7.5
10
.99
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38
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-20-
Figure 12.
Energy margin
Table 6.
versus
temperature
39
for the
tests defined
in
-21-
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2.11
Critical Temperature Tests
These tests are designed to determine where current sharing begins
at temperatures above 4.2 K. The initial condition will be zero mass flow
at 2.5 atmospheres. -The heater will be energized and the temperature of
the crossover turn of subcoil B will be allowed to stabilize.
This temperature will be measured by CGR's labeled BT-90 0 and BT-270 0 (See Appendix 3).
The HTFT will be raised to a specified background field and the 12
Tesla Coil current slowly ramped until the critical voltage is reached.
Figure 15 shows load lines plotted with estimated critical current characteristics for temperatures from 4.2 to 10 K.
2.12
Steady-State Current Sharing Tests
These tests are designed to study the stability of the coil in prolonged current sharing. The idea is to raise the background field while
the test coil is at zero mass flow, 2.5 atmospheres, and 4.2 K, and then
slowly ramp the test coil current until voltage is developed in the crossover turn.
Current will then be held at this level from 1-5 minutes.
2.13
Quench Propagation and Helium Expulsion Tests
These tests are designed to measure quench propagation, velocity,
pressure at the ends of the subcoil, temperature at the ends of the subAll quench tests will be
coil, and mass flow of helium out the ends.
done on subcoil B.
2.13.1
Quench Propagation
The initial
condition will be zero mass flow at 2.5 atmospheres and 4.2 K. Figure 16 gives an estimate of the time required
for the normal zone to reach the ends of subcoil B when coil curIn general, either raising the
rent is varied from 0 to 20 kA.
joule heating of the conductor or raising the ambient helium temperRaising
ature will increase the velocity of the normal front.
pressure above 2.5 atmospheres will lower the velocity of the normal
front.
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IIIIIIHIIIiiiHNN NH
Figure
16.
Estimated time f or normal zone to propagate 20 m as a function of coil current.
Assumes helium at 4.2 K and 2.5 atmospheres.
The half length of each subcoil is approximately
20 a.
44
-26-
This series of tests will be approached with great caution
to prevent a possible quench of the HFTF.
When the 12 Tesla Coil
quenches and is dumped through its 2mQ dump resistor, the flux linkages with the six background coils of the HFTF will change.
The
transport currents in the background coils will increase somewhat
depending on the' nature of their power supply controllers.
The
maximum possible induced currents can be estimated by assuming the
background coils to behave as superconducting magnets in a persistent mode. Then the increase in current in a given background coil
is simply
Mi,7
Ali
17
-
Li
where
Ali
-
maximum induced current in coil i
Mi,7
-
mutual inductance between coil i and
coil 7 (12 T Coil)
Li
M
self inductance of coil i
17
-
prequench current in coil 7
Table 7 lists
parameters of the coil system for estimates of maximum
induced currents.
-t -
-27-
TABLE 7.
CASE
TURNS
Estimates of Maximum Induced Currents in HFTF Coils Due
to a Quench and Dump of the 12 Tesla Coil
(Maximum 17 - 20,000 A).
Li
M
Max I,
7
NO.
M7
Max 17
Li
CRITICAL
CURRENT
1
2,366
8.48 H
0.04 H
1,200 A
94 A
2,000 A
2
1,793
5.16
0.017
1,200
66
2,000
3
2,366
8.48
0.04
1,200
94
2,000
4
1,793
5.16
0.017
1,200
66
2,000
5
380
0.073
0.0044
5,000
1,200
7,500
6
380
0.073
0.0044
5,000
1,200
7,500
7
57
0.002
-
20,000
LEGEND:
Li
=
M7
W mutual inductance between coil i and coil 7 (12 T Coil)
Max I,
=
maximum operating current of coil i
W
(20,000 A)
self inductance of coil i
M7
Max 17 -
Li
M17
-
Li
46
-28-
In addition to inducing transport currents, the collapsing flux
of the 12 Tesla Coil will lead to AC losses in the six HFTF coils.
Assuming the 12 .Tesla Coil current to decay with an L/R time conis less
stant of about 1 sec (decoupled from the HFTF), maximum d
No.
5
and
No.
6.
Since
per
second
at
Nb
Sn
coils
than 3.5 Tesla
3
these coils are cryogenically stabilized and will operate at no more
than 67% of critical current, the AC losses due to the collapse of
12 Tesla Coil current should be tolerable.
2.13.2
Helium Expulsion
Helium expelled
from subcoil
B during a quench will pass
through venturi meters VM1 and VM2 (See Appendix 2).
pressure drop as a function
shown in Fig. 17.
2.14
The estimated
of mass flow through these meters is
AC Ripple Tests
The intent of these tests is to superimpose an AC ripple current on
The ripple current will
the DC transport current of the 12 Tesla Coil.
impose a steady-state heat load on the coil.
4-7
-29-
Figure 17.
a
mass
Pressure drop versus helium
611995A-5. See Appendix 1.
No.
for Venturi
flow
T-- 45
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PFC/RR-85-12
DOE/ET-51013-155
UC20b
MIT 12 TESLA COIL TEST RESULTS
Steeves, M.M.; Hoenig, M.O.
Duplicate
July 1985
Plasma Fusion Center
Massachusetts Institute of Technology
Cambridge, Massachusetts 02139 USA
i
-30-
APPENDIX 1 - Conductor and Coil Parameters
CONDUCTOR
The 12 Tesla Coil conductor is identical to that of the Westinghouse
LCP coil. Tables A.1.1 - A.1.3 list relevant conductor parameters. Figure A.1.1 shows a cross section of the conductor.
COIL
The 12 Tesla Coil consists of three (3) series-connected, doublepancake subcoils of nineteen (19)
turns each.
Each potted subcoil has
overall dimensions of 14.7 in ID x 33 in OD x 1.86 in H.
The subcoils
are separated axially by trapezoidal G-10 spacers that cover 50% of the
These spacers provide for secondary bath
load bearing surface area.
cooling of the 12 Tesla Coil.
Figure A.1.2 shows the relative distribution of spacers. Table A.1.4 lists coil parameters.
TABLE A.1.1
-
12 Tesla Program ICCS.
Outside Dimensions .................... 2.08 x 2.08 cm (.818 in x .818 in)
Outside Corner Radius ................. 0.46 cm (.18 in)
0.17 cm (.068 in)
Final Wall Thickness .................
Sheath Material ....................... JBK-75 Super Alloy SS
Void Fraction ........................ 32%
Cable Configuration ..................
Conductor Area (Including Sheath)
....
Cable Space Area (Metal Plus
Helium) ......... 0.................. .
....
Helix Factor ...............
-
6 x 34 (486 strands)
4.157
cm2
2.943 cm2
1.04
Cable Area (Perpendicular to
Sheath Axis) ........................
1.945 cm 2
Helium Area ..........................
0.973 cm2
2
Steel Foil Area ...................... 0.025 cm
Copper Area (Perpendicular to
1.202 cm2
Wire Axis) .......................
Noncopper Area (Perpendicular to
2
0.668 cm
Wire Axis)..............
Hydraulic Diameter
.
................
0.40 mm
49
-31-
TABLE A.1.2 - Parameters of Airco Multifilamentary
Nb 3 Sn Single Strand Wire
0.7 mm
..........
Diameter ................................
Copper-to-Noncopper Ratio .........................
1.8/1
Matrix ............................................
Bronze
Niobium Filaments Per Strand ......................
2,869
Filament Diameter ...
....
Weight Percent Tin .
................
..
......
. . .......
.......
3.5jim
13%
........
Resistivity Ratio ...............................
Resistivity (RRR-
Surface Coating
-
(3.2 + 0.48 B)10 1 0 Q'm
................
50, B)
12
50*
Tesla
Coil
Oil **
..............
Wire
+
Soap
Average of 8 samples, in batches of 1 and 7, fired separately for 30 hours at
750 0 C. Three wires from batch 7 were oil coated.
Oil
Near-A-Lard #250-H
(Drawing
Lubricant).
furnace
(CH 4 0H) vapor during reaction
trolled by CO monitor at coil outlet.
TABLE A.1.3 -
Wire
heat-up.
was
treated
Methanol
with
fraction
methanol
was
con-
Twist Schedule of 12 Tesla Coil Cable
(Identical to LCP Westinghouse)
TWIST PITCH
CABLE ELEMENT
1 (Single Strand)
2.5 cm* (
1 in)
31 (Triplet)
2.5 cm
(
1 in)
32 (Triplet of Triplets)
3.8 cm
(1.5 in)
33
7.6 cm
(
3 in)
34
15.2 cm
(
6 in)
6 x 34
30.5 cm
(
1 ft)
When triplets are made, individual strands are internally twisted on the
same pitch as the triplet.
50
-32-
SUPERCONDUCTING
STRAND
HELIUM FLOW
CHANNEL
STAINLESS
STEEL SHEATH
Figure A.1.1
Cross-section of the 12 Tesla Coil conductor.
51
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-34-
TABLE A.1.4 -
12 Tesla Coil Parameters
Number
of
Pancakes .........
Number
of
Subcoils ...................................
Number
of Turns Per Subcoil ..........
Number
of
Potted
subcoil
Potted
Subcoil OD......
Turns Total
Potted Subcoil
ID ......
'.......................
....
6
3
...................
...--..............
....
.................
19
57
.........
...
.............
....-............. .
Height .........................
14.7 in
.....
...
33 in
. .
1.86 in
Inner 'Compression Ring ID x Thickness ...........
14.00 in x 0.34 in
Outer Compression Ring OD x Thickness ....................
39.25 in x 0.625 in
Case Height*
6:v
(...0
t17
S -, 04r,
C H ....... .......................................
o
Self Inductance ...
6.34 in
o ... ........-.......................
Charge Rate at 0.1 Volt
2 mH
-..................................
Dump Resistance (Per LLNL) ..................
...........
.
50 A/S
2 mR
Discharge Time Constant (Isolated Coil) ...................
1 sec
Maximum Terminal Voltage for 20 kA Discharge ..... . ...
. ....
40 Volts
C.0
rt ILL
Olt
53
-35-
APPENDIX 2 - Helium Supply System
OVERALL FLOW CIRCUIT
The helium supply system is shown in Fig. A.2.1.
Table A.2.1 defines
the symbols shown in the figure. It is assumed that a 100 psig, 300 K
helium source is available. Flow from this source will be regulated by
valve VR1 and will pass through two heat exchangers supplied by LLNL.
The 77 K helium will then pass through station STO7 and into the 2 meter
diameter cryostat.
There is a manifold at the inlet of the counter flow
heat exchanger that divides flow into two separate paths.
PRIMARY FLOW CIRCUIT
The principal path, and one of highest interest, is through a liq-
uid helium heat exchanger and into subcoil B.
by two cryogenic valves VC1 and VC2.
Flow into B is controlled
In normal operation, VC1 is open
and VC2 is closed, by-passing venturi meter VM1. The outlet flow from
subcoil B passes through venturi meter VM2, back through the counter flow
heat exchanger, and out station STO4 to be collected by the helium recovery system. Figure A.2.2 illustrates the primary flow circuit con-
taining subcoil B. When quench tests of B are carried out, valve VC1
will be closed and valve VC2 opened. Thus all helium expelled from the
coil will pass through the venturi meters and through the room tempera-
ture flow meter.
Note that when steady-state mass flow tests of B are
carried out, the parallel flow path through subcoils A and C will be
closed by closing ball valve VB5.
54
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TABLE A.2.1 - Definitions of Symbols in Helium Supply System Schematic
CF HX
Counter flow heat exchanger
..................
.................
0
Dielectric break
DB
...
0... 0.... ..
..
..
...
6. ..
..
...
.
..
Filter
F
0.. ...
0. ..
...
0. . ...
0. . ..
..
....
..
..
. ......
0
Flow meter
FM
...
.. 0.... 0... 0. .. 0. .. 0.....0..0..
. ...
0...
.....
.
. ...
.....
0
..... 0
LHe HX
Liquid helium heat exchanger
0....
..
..
..
.. 0. .. 0. .. 0...
..
..
..
. ..
. ....
Pressure measurement point
P
.0. . ...
..
..
....
0. . .. 0. ...
Station (point of piping
connection)
ST
0....
. . ...
0.... ...
0. ..
. ...
0. .. 0. ...
......
....
0..0. . . ....
...
.. ..
0
Temperature measurement point
T
0..0..0..0..
...
0. . . .. 0...
0.....
.
Ball valve
VB
0.. ..
.. 0. . .. 0. .. 0. .. 0...
. ...
0......
VC
Cryogenic hand operated valve
......
..
...
....
0..0..0. ..
0. .. 0. . .....
0. ..
.. 0...0. .. 0..... .
Check valve
VCH
. .......
..
...
..
0.. ..
......
0
VR
Regulator valve
. .....
0..0. . . . ....
0. ...
..
.. 0..0. ...
0..0....
VS
Safety relief value
0...
0..0. ...
0...
. ....
0..0..0.....0. . .. 0. ......
VTH
.
Throttle valve
58
-38-
SECONDARY FLOW CIRCUIT
Figure A.2.3 shows the secondary flow path through subcoils A and C.
This path will not be used in flow tests unless there is a failure of pulse
coil B.
OVERPRESSURE PROTECTION
The flow inlets and outlets of each subcoil are protected by pressure
relief valves VS1-VS6. These valves will relieve at overpressures of 400
psia.
VENTURI METERS
Figure A.2.4 shows a cross-section of one of the two venturi meters
at the outlet of subcoil B.
Both meters have a throat diameter of 0.080
in (2.03 mm).
59
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____
BULLETIN NUMBER 76-02
CRYOGENIC
/V(I
VALVE - BRONZE
k't
-
r-..-
C-e.-l ,/
e
r
ES8 VALVE FEATURES
These extended stem cryogenic globe valves
provide absolute shut-off for cryogenic fluids.
Their self-aligning,
resilient Kel-Fo seat seal
assembly permits tight shut-off in adverse oper'I
ating conditions and backseating permits replacing of the stem seal without reducing system
pressure
,
should it ever become necessary.
Extension tube and stem are fabricated from
304 stainless steel for strength and low conductivity which insures that the handle and stem
packing remain at ambient temperature during
continuous operation with any cryogenic fluid. It
should be noted that these valves are equally
effective at isolating the packing and handle
from the high temperatures of steam or other hot
fluids . The body and bonnet are pressure tested
and fabricated from corrosion resistant bronze
per ASTM 62-1.
* Trademark-DuPont
ES8 VALVE
6
*Low conductive stainless steel extension
body
*L
ES8 SERIES BRONZE VALVE
SERIES
*Proven Kel-F seals and 300 tapered seat
*Economic, reliable service for most
cryogenic fluids
62
?
4
ITEM:
SERVICE:
czzczzz(zZJiD
RANGES:
-
CONNECTIONS:
E
IPS threaded ends per ANSI B2.1
Socket ends per ANSI B16.11
Other ends available on request
OPEN
3
Extended-stem Cryogenic Valve
Liquids; nitrogen, natural gas
(methane), oxygen (with special
cleaning and packaging)
Operating temperature ± 400 F
Operating pressure 300 PSIG
(150 max.PSIG when above 2200
Proof pressure 450 PSIG
4
MATERIALS:
6.0
ITEM
PART NAME
SIZES
1.
2.
3.
4.
5.
Packing Gland
Packing
Ext. Tube
Ext. Stem
Seat Seal
MATERIAL (Specification)
TYP. ALL
Bronze (ASTM B-62) (N.A.)
Teflon Impregnated Asbestos
Stainless Steel (ASTM A-269)
Stainless Steel (MIL-S-25043)
Kel-F
S GAT x k( - F
Remainder of parts: Pred. pem (ASTM B-62)
WEIGHT (APPROX.)
DIMENSIONS: (NOM.)
-
----
---
SIZE
"A"
"B1"
1/2"
3/4"
1"
1 1/2"
2"
2 11/16
3 3/16
3 3/4
4 3/4
5 3/4
10
11
11
13
14
SIZE
3/8
1/8
3/4
1/16
1/2"
3/4"
1" 11/2"
2"
WT. LBS.
1.7
2.5
3.9
8.3
12.9
A
Oro
-t 't
4
&
r) N G7
sw
ORDERING INFORMATION:
SIZE
LINE CONNECTIONS
PART NUMBER
1/2"
3/4"
Female Pipe Thread
"
"
"
ES8-84-2T1
ES8-86-2T1
ES8-88-2T1
ES8-812-2T1
ES8-816-2T1
1"
1 1/2"
2"
1/2''
3/4"
1"
1 1/2"
"
"
"
"
"
"
"
"
"
Socket Solder, Pipe Size (IPS)
"
"
"
"
"
"
"
"
"
2"1""1
Cryolab
ES8-84-2WP1
ES8-86-2WP1
ES8-88-2WP1
ES8-812-2WP1
ESd-816-2WP1
BOX 6008 - LOS OSOS, CA. 93402
63
(a S*-mdI5
-41-
APPENDIX 3 -
Instrumentation
Instrumentation for the 12 Tesla Coil can be arbitrarily divided
into four groups: voltage measurement and heating systems; temperature,
pressure, and flow measurement systems; coil current and magnetic field
measurement systems; and acoustic measurement systems.
VOLTAGE MEASUREMENT AND HEATING SYSTEMS
Figure A.3.1 is a schematic of the voltage measurement and heating
systems.
Shown are voltage taps, the pulse coil heating system, pulse
pick up coils, and the heater wire heating system.
Each of the three subcoils has twelve (12) pairs of voltage taps as shown. Note that each subcoil has nine (9) turns per pancake and one (1) crossover turn to yield a
total
number of turns per subcoil equal to 2 x 9 + 1 - 19 turns per subcoil. Thus the entire coil has 3 x 19 - 57 turns.
In addition to the
3 x 12 - 36 pairs of voltage taps on the coil, there is one (1) pair of
voltage taps across the entire coil (VT 14) and four (4) pairs across the
termination lap joints. Therefore, the sum total of voltage tap pairs is
36 + 1 + 4 - 41 pairs total.
Figure .A.3.2 shows the voltage tap placement
on a typical subcoil.
Wire color codes are also given.
Note that the re-
ference view in A.3.2 is in the direction of gravity.
Figure A.3.3 illu-
strates
lap
the voltage
tap placement
on the termination
A.3.1 lists the numbering of all voltage taps.
joints.
Table
F,'1 At.-f 7, 11e
-42-
(CO-11 J)
- 0 vtt4 Y__ ftlt,-3w4,v
f4,-a
AK-4 qe4i* A
LC Ct4)
?ick up
Vnres
VM
A
Y-rJA
r
4-~Z
VIT
e,
Vr
n,e
vfr
e
VU
A
k.
4.),2
,
YT
4C
rt.pjo., ~
*.,L
-ie
,
ct
14 4L4
C.~~~
c.
tjoav
w
-
W r
-p
Figre A.;i3
Figure A.3.1
Schematic of 12 Tesla Coil voltage tape, pulse coil Ubating
sytem, pulse pick-up coils, and heater wire heating syutem.
65
I
-43-
"1-
V j1
80
00 Ref.
,-
VT< -
VT7
VT 172.'
?-
-e
Level 2, 4 and 6
Level 1, 3 and 5
GTS
VT Io -
VT4
VT1 -p,,.
VT3
VTa -
Ref.' View
k,-
CT
- Vt 7-VT.
ukA/ JZI
S'irj
- V Tl10
Figure A.3.2
-
Tr
Crossover Turn
Schematic
66
of
voltage
tap placement
on
typical
subcoi:
-C -
---
A
e,4
I
IM 6 13
g: R4-Iv .
-&
A
--
A.at{
-
Vt
-3
3
-
-~-C.
~
~
t-
Figure A.3.3
Voltage tap placement on termination lap joints. Also shown
are VT
the voltage taps across the entire coil.
14,
67
-45-
-
TABLE A.3.1
-
Voltage Tap Numbering. Taps are Stranded
No. 28 Wire Insulated With Type - E
Teflon.
SUBCOIL
CROSSOVER
TOP
BOTTOM
ENTIRE
SUBCOIL
LAP
JOINTS
COLOR
TAP
POSITION
A
C
B
NUMBER
CODE
VT
1
White/Red
Stripe
No. 11
No. 23
No. 35
VT
2
Blue
No. 12
No. 24
No. 36
VT
3
Orange
13
25
37
VT
VT
4
5
Purple
Gray
14
15
26
27
38
39*
VT
6
Brown
16
28 Yr Il-b1
40
VT 7
VT 8
VT
9
VT 10
Blue
Orange
Purple
Gray
VT 11
Brown
VT 12
White/Black
Stripe
VT 13
Blue
VT 14
Orange
No. 29
30
31
32
21
33
45
No. 22
No. 34
No. 46
Lead A
A-B
B-C
Lead C
Lap Joint
Lap Joint
Lap Joint
Lap Joint
No.
2
No.
No.
No.
1
No.
1
ENTIRE
COIL
* Wire broken --
will not work
W0 1 No.
No. 17
18
19
20
41
42
43
44
3
4
-46-
individual
Tfie pulse coil heating system consists of three (3)
The pulse coils
pulse coils, one on the crossover turn of each subcoil.
consist of approximately 300 turns of .075" x .150" copper wire insulated
Pulse
with double dacron glass insulation to a build of .005" per side.
Pulse coil B is of
coil layers are insulated by epoxy-glass and Kapton.
primary interest, since it surrounds the crossover turn at the highest
The three
magnetic field point in axial center of the 12 Tesla Coil.
pulse coils have a common lead as shown in Fig. A.3.1, so that four (4)
cables are needed to connect them to the room temperature power supply.
Pulse coils A and C provide double redundancy in the event of an insulaThe power supply consists of a nominal
tion failure in pulse coil B.
87,000aF capacitor bank behind an ignitron switch.
The ignitron is triggered by a voltage pulse from a pulse generator that is part of the power
supply package.
A shunt of 200uV/A is connected in series with the capacitor bank and will be used to manitor the current into a given pulse
coil.
In Fig. A.3.1, R.1 represents the resistance of the series shunt
The capacitor bank
and V.1 the voltage across it due to a current pulse.
voltage will be measured by a voltmeter. The expected range of capacitor
voltage is from 0-AK volts.
The expected current pulse width is 10 ms.
Table A.3.2 lists
parameters associated with the pulse coil heating
system. Figure A.3.4 shows the geometry of a typical pulse coil.
TABLE A.3.2 -
TURNS
INDUCTANCE
Parameters Associated With the Pulse Coil
Heating System
PULSE COIL
A
PULSE COIL
B
PULSE COIL
C
287
304
304
72j H
81 UH
81iiH
R.T. RESISTANCE
.............................
CAPACITANCE
. .. .....
......... .........
PULSE WIDTH
87,00O0F
10 ms
1-100
.... .... .... ....
VOLTAGE RANGE
....
...
0-'se
V
200.pV/A
SHUNT VOLTAGE
PEAK CURRENT AT 5-06
V
...........
quo~
69
> 10,000 A
-47-
20
VT-1
0 0 Re
Ref. View
"dir.'/6vu-
CGR
CGR
(back side)
270
a 131
Pulse
Pickup.
Coil
Pulse Coil
1 '
-p
G-10 Filler
_
Surface Mounted CGR
Ref. View
Section at ~850
Figure A.3.4
Sketch showing placement of carbon glass resistors,
coil and pulse pick-up coil.
70
pulse
-48-
The pulse pick-up coils consist of three (3) 20 turn coils of No.
There is one pick-up coil per
28 stranded wire insulated with teflon.
pulse coil.
These coils are magnetically .coupled to the pulse coils and
give voltage signals proportional to the time derivative of flux generated
by the pulse coils.
Figure A.3.4 shows the location of a typical pulse
pick-up coil. Table A.3.3 lists
the color code and numbers associated
with the pick-up coils.
TABLE A.3.3
Pulse Pick-up Coil Color Codes and Numbers
SUBCOIL
COLOR
NUMBERS
A
B
C
RED
RED
RED
1
3
Subcoil B contains an imbedded heater wire made by ARi Industries
Inc. The wire consists of an Inconel heater insulated by magnesium oxide
and encapsulated in a 347 stainless steel sheath.
The heater wire has
an RRR = 1.05 and a resistance at 4 K of 31.2 mg/cm, yielding a total
resistance at 4 K of approximately 120.
Table A.3.4 summarizes heater
wire parameters.
A forcing voltage of 300 volts. will be sufficient to
supply heater currents for this experiment.
TABLE A.3.4
OUTER
DIAMETER
HEATING ELEMENT
INSULATION
JACKET
RRR
Heater Wire Parameters
.........................
0.063 in
........................................
INCONEL
MgO
....................................... o.......
347 ss
........ o.............*.........o.............. ......
1.05 ± .02
................ ......................o...............
RESISTANCE PER FOOT AT 20 0C
RESISTANCE PER CM AT 4.2 K
RESISTANCE AT 4.2 K
MAXIMUM
.......................
...
31.2 mD/c
............................
.....................................
FORCING VOLTAGE
10/ft
.
.......................
71
-
...........
120
0
300 V
( ~ViJ~ ) <7
-49-
TEMPERATURE, PRESSURE AND FLOW MEASUREMENT SYSTEMS
Figure A.3.5 shows simplified schematics of the primary and secondary flow circuits. Most of the 12 Tesla Coil experiment will be done
with zero helium mass flow.
However, when flow experiments are undertaken, the present helium supply system allows for flow in subcoil B,
while subcoils A and C remain at zero flow.
Thus, flow experiments will
be focused on subcoil B.
The arrangement of temperature, pressure and flow instrumentation
is shown in Fig. A.3.5. Temperatures are measured by carbon glass resistors located at the inlet, center and outlet of each subcoil.
The CGR's
at the inlet
and outlet
measure helium temperature, while those at the
center measure sheath temperature.
Figure A.3.4 shows the locations of
CGR's at subcoil
the CGR's.
centers.
There are a total
Table A.3.5
lists
of eleven (11)
parameters associated with
CGR's yielding 44 lead wires.
TABLE A.3.5 Carbon Glass Resistor Parameters
(Lake Shore Cryotronics Model CGR-1-2000)
WIRE CODE
FIG. A.3.5
NUMBER
SERIAL
NUMBER
LOCATION
T1
C4678
Inlet
BT-270 0
C4676
Center -B
4
4
BT-90 0
C4674
Center -B
3
T2
C4681
Outlet -B
T3
C4719
Inlet
GREEN
No.
No.
7
WHITE
7
No.
BLACK
7
MAX.
LEAD
RESISTANCE
(4.2 K)
SUPPLY
VOLTAGE
7
1.91 kQ -'
10 mV
4
4
2.07 v-
10
3
3
3
1.83 v"
9
8
8
8
8
2.21
-A
9
9
9
9
2.17
10
C4670
Center -A
2
2
2
2
1.76-
9
C4072
Center -A
1
1
1
1
1.79
9
T4
C4722
Outlet -A
10
10
10
10
1.76
9
T5
C4750
Inlet
-C
11
11
11
11
1.94 -
10
CT-270 0
C4703
Center -C
6
6
6
6
1.78 v
9
CT-900*
C4677
Center -C
5
5
5
5
1.88 V
9
T6
C4751
* Wire broken
Outlet -C
12
12
12
12
AT-270
AT-
-/
-B
YELLOW
FOUR
0
900
72
No.
-A
2.01 /
_
/
10
10
-I
I
-
I~,EJd~.A
(I
______
CL4 47(o
AqT7O0
C 44 10
~T- l 0
C io'7-L
TT
c 47so
C.- 270'
CTr- 00
C'?o73
C47 7
_____
______
_____
0 o-f2-
Cl q678
aS-r-2Z70 0
2L
~
9,07
7.(o
/5.4
73
-
1o
147q5.9
1-IN
j'1iOXL
0-
cefc- -I L79
ILt - C.
t.dc
11K)
a. SL2
I qQ
Cl--A
(77,
bAC
s"P
I-T.
1T9 0
174
Wo
'3z. o
78o
o8
I ~
I.
SERIES CGR-1
CARBON GLASS RESISTANCE
TEMPERATURE SENSING ELEMENTS
Technical Specification: CGR-1
SERIES CGR-1 CARBON GLASS RESISTANCE
CRYOGENIC TEMPERATURE SENSING ELEMENTS
e
*
*
9
9
Stable
Excellent in Magnetic Fields
Monotonic R vs T and d 1nR/d 1nT
1 to 300 Kelvin Range
Rugged Construction
The CGR-1 series Carbon Glass Resistance Temperature Sensors represent the best choice for a highly reproducible
temperature sensing element for the range 1-300 K in high magnetic fields. The full temperature range capability extends the
usefulness of the CGR-1 series (over Germanium Sensors) in applications not involving high magnetic fields.
The configuration of the carbon glass sensing element is the result of an extensive computer aided design analysis based on
a primary requirement that the element be of the classical four lead potentiometric configuration. The result is an element
typically 4 millimeters long with half millimeter voltage ears.
Each of the models listed in table I are designed-nd optimized for the specific recommended temperature range with
emphasis on achieving specific sensitivities (d 1nR/d 1nT) over the recommended range. Each model will exhibit monotonic
response to 300 K regardless of the recommended range.
Every completed CGR- 1 sensor is quality tested to assure that the encapsulation is leak tight and the sensor is stable when
cycled from room temperature to liquid helium temperature.
Typical response to magnetic fields is shown in Table 11.
TYPICAL SENSOR SPECIFICATIONS:
Temperature Reproducibility: =0.00075 K Maximum (:0.005 K Typical) when thermally
shocked between room temperature and liquid helium
Size: 3mm (0.120") diameter by 8.5mm (0.335") long cylinder, four (4) each 6" long phosphorbronze insulated leads having epoxy strain relief at sensor. See figure on reverse
side. Special packages available on request.
Internal Atmosphere: Helium 4 is Standard. Helium 3 or Nitrogen are available as options.
Materials of Construction: See construction details on reverse side.
Data Supplied: All testing and calibration data supplied is measured with D.C. power. Included with each
uncalibrated sensor are a 2-wire (continuity) resistance at ambient, liquid nitrogen, and
liquid helium temperatures; and 4-wire (potentiometric) resisiance at ambient, liquid
nitrogen, and liquid helium temperatures. These values should be considered as nominal
rather than precision calibration data points.
TABLEI
Typical Resistance at 4.2 K (ohms)
Model
CGR-1-50C
350-750
CGR-1-100C
750-1300
CGR-1-1500
CGR-1-200C
Suggested Useful Range (Kelvin)
1300-1750
1750-2400
1 to 77 (300)
1.5 to 100 (300)
2 to 100 (300)
2.5 to 100 (300)
Consult factory for availability of other resistance values
TABLE I
Typical Magnetic Field-Dependent Temperature Errors' for Carbon Glass Sensors
14 tesla
2.5 tesla 8 tesla
T(K)
4
1.5
0.5
2.1
6
3
4.2
0.5
1.5
<0.1
0.5
15
1
0.5
< 0.1
35
1.5
0.5
0.1
<
77
SERIES CGR-1 CONSTRUCTION DETAIL
3mm
-(0. 120")
Lead Identity for Carbon Glass Resistor
A
0
C
QD
D
0
Lead Color
Yellow
Green
White
Black
Index Mark
V
V
A.
0
B.
C.
D.
E.
-
B
Key
+I
I
C
D
8.5mm
(0.335")
A
E
Limit R
F
G
VEMF
oCurrentr
C
YV+
W~
L-
A. Gold-plated copper enclosure
B. Current contact zone
v- G
-- - ----
--
,-Bk
C. Phosphorus-bronze leads 0.20 mm (0.008" dia.)
0. Sensing element
E. Gold leads 0.05mm (0.002" dia.)
F. Epoxy heat sink
G. Beryllium oxide base
CGR-1 Resistor
Basic Measuring Circuit
(voltage drop across sensor
should be kept to 10mV or less)
CGR-1 CARBON GLASS RESISTANCE THERMOMETER TEMPERATURE VS. RESISTANCE TYPICAL CURVES
Recommended
Current (Maximum)
0.1 uA
-
... L
-
--
--
--
--
-.
-
-.
-
1 uA
10,000
I
-
Resistance
(ohms)
-
-
-
-.
-
-
-
-
-
10 uA
1,001
~J.
-
ie-.
-
-
-.
-
-
-
-
N
100
I
i
I
I
X
1XXI
I
I
I
I
I
I
I
IlUUUA
N
10L
1
1L
I
10
:
100
300
1 mA
_114r, Z _u f
I4
LAKE SHORE CRYOTRONICSINC.
64 EAST WALNUT STREET
WESTERVILLE, OHIO 43081
DIP TEST DATA FOR:
SENSOR MODEL: CGR-1-2000
SERIAL NO.:
C4750
DATE:
16-NOV-83
TWO LEAD RESISTANCE(I+ TO I-):
ROOM TEMPERATURE
LIQUID NITROGEN(77.4K)
LIQUID HFLIUM(4.2K)
0.16E+02
0.32E+02
0.36E+04
OHMS
OHMS
OHMS
FOUR LEAD RESISTANCE
ROOM TEMPERATURE
LIQUID NITROGEN(77.4K)
LIQUID HELIUM(4.2K)
0.887E+01 OHMS
0.174E+02 OHMS
0.194E+04 OHMS
.4-
SELF-HEATING CONSIDERATIONS:
TO MINIMIZE SELF-HEATING DURING CALIBRATION
LAKE SHORE ADJUSTS THF CURRENT
TO THE SENSOR TO MAINTAIN
SENSOR OUTPUT VOLTAGE AT THE
LISTED VALUES:
ABOVE 1 KELVIN
0.1 TO 1 KELVIN
BELOW 0.1 KELVIN
1 TO 3 MILLIVOLTS
0.1 MILLIVOLT
0.03 MILLIVOLT
MAXIKUM ALLOWABLE CURRENT TO AVOID DAMAGE
TO SENSOR IS 200 MILLIAMPS
LEAD COLOR CODE:
WHITE:
I+
BLACK:
I-
YELLOW: V+
GREEN:
V76
4
-50-
F: A_A
4,3-11
vCi
B
DPZ
P2.
2
LO
S
Figure A.3.5
Simplified
cuits.
'
3
7
Se
S
C-
CowCirc
;+ -
schematics
S,,Ls
of primary
A C
and secondary
flow cir-
-I-,i o
-51-
Absolute pressures are measured by sputtered strain gauge transducers (CEC 1000).
These devices have a pressure range from 0 to 1000
psia.
Table A.3.6 lists
parameters associated with the pressure transducers.
There are a total of five (5) PT's yielding 20 lead wires.
TABLE A.3.6
Absolute Pressure Transducer Parameters
MODEL
EXCITATION
CEC 1000
10 V dc rated;
..................
................
PRESSURE RANGE ..............
.
.. .
0
15 V dc max.
- 1000 psia
WIRE CODE
FIG. A.3.5
NUMBER
SERIAL
NUMBER
LOCATION
RED
PURPLE
GRAY
BROWN
No.
5
No. 5
No.
P1
.62a4-
P2
4.6242
Outlet -B
6
6
P3
4+2t5-
Inlet
-A
7
16046-
Outlet -A
8
Inlet
-B
No.
5
INPUT
RESISTANCE SENSITIVI
(200 C)
5
-4O3.
6
6
-42
7
7
7
992
8
8
8
464
2973-mUi
2
P4
g 0
P5
2t(L4'4
P6
0 cj
Od_ U 4 - (It is worth noting that the PT's contain magnetic materials and will
therefore require good mechanical support. They will be located in the annular gap between the HFTF coil stack OD and the cryostat ID.
Supercritical helium mass flow will be measured using two venturi
meters with differential pressure transducers. The differential pressure
transducers are made by Validyne Engineering Corporation.
The vendors
wiring diagram shows each device to have three (3) wires.
Therefore, there
V'_i-V'
o'tt. s
(:1~
78
9
-52-
will be a total of six (6) wires required for the differential pressure
measurements. Table A.3.7 lists parameters associated with the differential pressure transducers.
TABLE A.3.7
Differential Pressure Transducer Parameters
Validyne P10
MODEL
EXCITATION (Supplied
by MIT
OUTPUT
5 V rms, 3-5 kHz
30 mV/V full
scale nominal
± 80 paid
.............
PRESSURE RANGE
WIRE CODE
FIG. A.3.5
NUMBER
SERIAL
NUMBER
LOCATION
WHITE/
RED STRIPE
WHITE/
BLACK STRIPE
ORANGE
DP- 1
Inlet
-B
2
2
2
DP-2
Outlet -B
3
3
3
COIL
CURRENT AND MAGNETIC FIELD MEASUREMENT SYSTEMS
Coil current will be measured using a shunt that is part of the LLNL
power supply. See Fig. A.3.6.
Magnetic field at the 12 Tesla Coil midplane will be measured by a Hall probe located in a hole in the HFTF inner
compression ring.
Parameters of the Hall probe are given in Table A.3.8.
This device has four (4) wires.
TABLE A.3.8
MODEL
.........
EXCITATION
.
.........
......................
........
.........................
BELL BHA-921
100
mA
Constant dc Current
6.52 mV/Tesla
......................................... 2083
OUTPUT RESISTANCE
O.6989
...........................
ZERO FIELD INPUT RESISTANCE
ZERO FIELD
Hall Probe Parameters
* ............................
MAGNETIC SENSITIVITY
SERIAL NO.
See Fig. A.3.6
o.........,......
O.6262
WIRE CODE:
CONTROL CURRENT
HALL VOLTAGE
.............
...........
...
o.*.............
. ..
79
........
RED-50, BLACK-50
BLUE-50, ORANGE-50
a
~:,
~--a-3-
.~
1 -'-a
P.-4c
4-A
u
~
f
Figure A.3.6
A
44A
Schematic of Hall probe location and current shunt.
Current
into the lead of subcoil A produces a downward magnetic
field (in direction of gravity).
80
1TpI.a-(
*Vpuul
PTP%"g
'VIIIP'7
-54-
ACOUSTIC MEASUREMENT SYSTEMS
Six differential
the 12 Tesla Test
Coil
style acoustic emission sensors were installed on
on
Wednesday,
April
18,
1984.
The coil is con-
structed of three subcoils.
A sensor is attached to both leads of each
subcoil (See Table A.3.8).
Five of the six sensors are attached to the
lead wires inside the coil case.
They are well protected. Only sensor
#10, on lead A Level 1, is exposed.
The sensors are held in place by G-10 strips which act as springs.
Mylar tape electrically insulates the sensors from the coil.
The cable
running from each sensor is white teflon coated, shielded, twisted twinax (Belden #83316).
TABLE A.3.8 - Acoustic Sensor Layout
LEVEL
PANCAKE
SENSOR
RELATIVE
SENSITIVITY
1 (Defined)
1
A
10
2
A
16
2.7
3
B
13
2.5
4
B
15
2.2
5
C
14
3.0
6
C
11
1.5
Sensors numbered on end of cable
81
-55-
1.
TJ~}
L~L~
Lw~ I
Le~4
4.f
I
~mm~;~z
82
Figure A.3.7
Acoustic sensor locations.
-II
kz
1,
~V
rf
D.2
0k3
It-
41r
iLI-4o VC10-zLufuj a________
0
I
al- a 10
e? rl 's-/
Lji
u-jC- kz'
.
It
a
83
-56-
APPENDIX 4
-
Termination Lap Joints
DESIGN CONSTRAINT
The 12 Tesla Coil lap joints are constrained by the physical size
The principal restriction involves lap joint length
of the HFTF cryostat.
as shown in Fig. A.4.1.
DETAILS
There are four (4) termination lap joints associated with the six
Each termination has been swaged
(6) terminations of the 12 Tesla Coil.
to a final diameter of 0.775 inches (2 cm) and has a cross-section similar
The terminations are approximately 9.75
to that shown in Fig. A.4.2.
inches long. The ends of the terminations are plugged by 1/8 inch copper
reaction
Leaks in the welds, found after
caps that have been welded on.
of the coil, have been plugged by brazing.
Lap joints have been made with pairs of OFHC copper blocks of geoLap joints have been made by soft soldering
metry shown in Fig. A.4.3.
The solder composition
pairs of these shunt blocks to the terminations.
Estimated lap joint resistance is approximately 1-2 n.
is 60/40 (Sn/Pb).
84
-57-
-577,A.d& A. (z4 1 J1~y
95 cm 1R
/e
I
13c.;i-k
I
I-I-CI
7f
L.
3
S.i
4
04
*
7o
0o
too
R (cm)
Figure A.f.l Relative position of the 12 Tesla Coil termination
lap joints in
the Livermore High Field Test Facility (HFTF).
Coil lap joints
are constrained to lie in a 5 cm gap between two stainless steel
flanges. The approximate field profile at the lap joints is also
shown.
85
U,
roee
*.-~Oso
I4 fis
v.
N
Figure A.4.2
Typical
termirfation 'crcas-section
86
(diameter
-
0.775
in).
I
..--
-
-
-
-
. -
-
R
-3
1
MAT'Ll.
CDA IOZ
COPPER (OFMC)
-
.34. Rys
TO
1
LEAD
T
.2ST
SHUN*T
iJO.1 DMI
S
PAIL
Figure A.4.3
CD0A IOZ COPPIER COPwH)
JbiNT
SHUNT
DMIL
Copper shunts used in 12 Tesla Coil termination lap joints.
.3qet
-60-
APPENDIX 5 - Transient Stability Model
MAGNETIC DIFFUSION TIME CONSTANT
The approximate magnetic diffusion time constant
of the Airco 0.7
mm diameter wire at 10 Tesla is
Tm =
2
(cuAr)
. (4
0a
x
10-7)(1.25
x
109)(1.5
x
10-4)2
-
35
ys
where
ah e
=
copper stabilizer conductivity [Q_*m.
Ar
W
copper stabilizer radial thickness [m]
3
Thus for AC fields at approximately 50 Hertz (T - 20 me), one can assume
complete penetration
of the magnetic field into individual strands.
ENERGY DELIVERY MODEL
The energy delivery model treats the ICCS inside the pulse coil as
the secondary of a transformer, a technique commonly used to analyze nondestructive eddy current testing.
At 50 Hertz, the frequency of interest,
hysteresis losses in the superconductor are small compared to eddy current losses in the wire.
* The model,
therefore,
is
solely one of eddy cur-
rent heating.
The cable and sheath are modeled as resistors that have
been reflected from the secondary to the primary circuit. The energy extracted from the capacitor bank in the first
half cycle divides in the
primary circuit according to the relative strengths of the primary reHence knowledge of the reflected resistors leads to an estimate
sistors.
of the energy delivered to the ICCS cable.
Figure A.5.1 shows the lumped parameter energy delivery circuit model.
It is worth noting that
the inductance L represents that of the pulse coil with a lossy core.
That is, the pulse coil inductance, as calculated in free space, is lowered slightly (~ 3%) by the presence of the ICCS.
'-'I-
Le&c1 &
IrniteIn
R
R
IC.
Skedt+I
RL
t
V0
II
Figure A.S.1
Lumped parameter energy delivery circuit model.
09
-o
ALGORITHM
An algorithm to calculate specific energy delivered to cable is presented below in Table A.5.1.
It states that the energy delivered to the
cable in- one half cycle equals the ratio of the reflected cable resistance
to the total series resistance multiplied by the total energy delivered in
one half cycle. It is assumed here that the switch is a rectifier that allows a half sine wave current pulse.
Parameters used in the energy delivery model are summarized in Table A.5.2.
TABLE A.5.1 - Energy Delivery Algorithm
1.
Energy delivered in one half cycle.
E 1/ '(1/2
E1/2o
CV 02)
[J]
initial stored
fraction delivered
in 1/2 cycle
stored energy
where
C
-
Vo W
2.
capacitance
[F]
initial voltage on caps
[V]
T
-
period of damped sine wave
[s]
T
-
time constant
[]
Period of damped sine wave.
2w
1
T
=-
-
-
LC
-
f
=
27
[s]
l-d
W
where
f
-
frequency
L
-
equivalent inductance (pulse coil with
lossy core plus stray inductance)
L
-
Lpc + Ls
d
-
--
[s-1 ]
[H]
2C
damping constant
0
4L
RT -
Rr X Ri
X
-
leads
s
-
sheath
c
-
cable
+ Rpc + Rs + Rc
-
total series
resistance
r
-
ignitron
pc
-
pulse coil
90
[-]
-0.3-
3.
Time constant
2L
R
T
4.
[s]
Sheath resistance
24
1
E
Rs
(
)
asro2r2E
f2
where
Ve
-
volume of sheath
-
pulse coil turns per unit length
as
-
sheath conductivity
ro
-
eequivalent outer radius
[Mi]
M
ratio of inner to outer radius
[- J
[M3
Np
-
tp
ri
--
ro
5.
Cable resistance
Rc
=
R1 , + RI
where
R1 1
-
a1R
-
2
2
Ri = Vc(
N)
RR
)2
2
Lf 20.
Cs
R
+ acuR2W2
sin2
2p
1 -64-
where
M
volume of cable metal
ac
-
conductivity of copper stabilizer
R
-
strand outer radius
[m]
R1
-
bronze matrix outer radius
[m]
p
-
angle between pulsed field and
strand axis
Lf
-
a1
=
A
-
am
6.
Em[3
3J
Vc
[
-
e
M-1 I
[deg]
filament twist picth
[m]
matrix conductivity
-a
]
[Am
fraction of superconductor in
matrix
bronze conductivity
-
[-]
[A
]
*m
Energy delivered to cable in one half cycle.
Rc
Ec
(J]
* E1/2
--
RT
7.
Energy delivered to pulse coil in one half cycle
Rpc
E[A
RT
8.
Current
V0
i(t)
e-t/T
sin wt
[A]
WL
V0
Ip
-
-
e-t/T
(A]
WL
92
to f T/4
9.
Specific energy delivered to cable
Ec
By volume:
ecV -
-
-
Vc
Ec
By mass:
ecm
-
-
mc
1
Rc
Vc
RT
-
1
-
* E1/2
-
Rc
-
VCYC
E1/2
RT
where
10.
Vc
-
cable volume
[M3
tm c
-
cable mass
[kg)
Capacitor voltage after discharge
Vc
M
Vo e-T/2T
93
[
VJ
TABLE A.5.2 - Parameters Used in Energy Delivery Model
C
-
87,000PF
Lpc
Rr
=
5 mQ
Ls
Vc
=
1.26 x 10-4 m 3
L
50,
B)
-
(3.2 + 0.48 B) x 10
y1m
100,
B)
-
(1.6 + 0.48 B) x 10
Sem
pcu(RRR =
p __ (RRR
-
-
81pH
19yH
-
100H
0.649 m
304
x L
486
ds
= 7 x 10-4 m
1.04
R
-
390
R 1-
N8p
Ns
=
fh
2.5 x 10LV
-
Vs
=
ps
-
ri
-
r
=
2
m
7.826 x 10-5
X
ai
67 x 10-8S2m
2.15 x 10-4 m
- 0.21
m
m3
3.5 x 10-4 m
- 1.1 x 10
-
1.68 x 107 a 1m-1
0.012 m -
R
= 45 m(
0.0103 m
Rp
-
94
a
5.65 x 10-4 (1.6 + 0.48B)
7.0 APPENDIX 2 - HFTF INTERFACE SPECIFICATION
The interface specification for the 12 Tesla Coil Program was issued as a reference
document to the four program participants in 1979. It describes the test coil design
requirements and other factors associated with the Livermore High Field Test Facility
interface.
95
INTERFACE SPECIFICATION FOR 12 T INSERT
TEST COILS (PRELIMINARY)
University of California
Lawrence Livermore Laboratory
Livermore, California
November 1979
96
INTERFACE SPECIFICATION FOR 12 T INSERT TEST COILS (PRELIMINARY)
Contents
1.
Design Requirements
2.
Coil Orientation
3.
Space Constraints
4.
Mechanical Interface
5.
Electrical Interface
6.
Diagnostic Equipment
7.
Thermal Interface
8.
Magnetic Interface
9.
Quench Protection
Sketch SK-1000:
Coil Data
Sketch Sk-1001:
High Field Test Facility--4 m Diameter Cryostat
Figures 2A, B, C, & D:
Typical Quench Performance
Dwg. AAA-79-104494-00:
Preliminary Layout of HFTF Coils
Dwg. AAA-79-112148-00:
12 Tesla Coil Assembly, Test Coil Lead Space
97
INTERFACE SPECIFICATION FOR 12 T INSERT TEST COILS (PRELIMINARY)
1.
DESIGN REQUIREMENTS
1.1
The conductors used in the test coils are to be candidate prototypes
for Tokamak E.T.F. toroidal field coils.
The conductors are, therefore,
to be designed to meet the following "modified E.T.F." specification:
1.1.1
Plasma major radius, - 5 m
1.1.2
Coil major madius, = 5.8 m
1.1.3
Coil bore size, 6 m horizontal x 10 m vertical
1.1.4
Coil shape, modified D-shape
1.1.5
Number of coils, 12
1.1.6
Field on plasma axis,
1.1.7
Peak field at the winding, 12 T
1.1.8
Conductor, Nb3 Sn or alloyed Nb-Ti*
1.1.9
Field profile, maximum on the center line
1.1.10
Amp turns/coil - 12 MA
-
5.8 T
1.1.11
Current density over winding pack, ie1700 A/cm 2 ; over
conductor,
i-tte- A/cm2
1.1.12
Operating current, 10 to 15 kA
1.1.13
Stored energy/coil, - 1500 MJ
1.1.14
Stability margin: one-half turn length at the high-field
region can withstand 100 mJ/cm3 without undergoing a quench.
1.1.15
Tolerance for pulsed fields*
A.
Normal operation
1.
B
:
0.15 T/sec for one second up, one second down
2.
B 11:
0.15 T/sec for one second up, one second down
3.
Repetition rate:
B.
Upset condition
one pulse every five minutes
Simulation of a plasma disruption by a downpulse in By of
0.5 T in 0.10 second with a repetition rate of once a week.
*As revised at 12 T meeting.
98
1.1.16
Tolerance for radiation, 1 x 109 rads
1.1.17
Vacuum topology:
bell jar with reentrant holes
It should be noted that the specifications are the minimum to be
achieved. If, for example, the Seller can obtain a viable design while
achieving a higher overall current density, then such an approach is
acceptable. Grading of conductor and structural design is left up to the
preference of the Seller.
1.2
The test coil is to be designed to meet the following criteria when
tested in the HFTF:
1.2.1
Carry design current (between 10 and 15 kA) in a maximum
field of 12 T.
2.2.2
Shall not quench when an energy of 100 mJ/cm 3 is
deposited in the conductor in the high-field region over the length
of half a turn and in a time not exceeding 50 msec. The thermal
environment of this portion of the conductor shall not be
significantly different from that in the remainder of the coil.
2.
COIL ORIENTATION
The toroidal field coils of a Tokamak operate with the axis
horizontal. Since the heat transfer properties of a pool-boiling
conductor may be affected by its orientation, arrangements will be made
for the test coils to be tested with the axis horizontal.
Sketch Sk-1001 shows this arrangement diagrammatically.
3.
SPACE CONSTRAINTS
The test coil will be inserted in the HFTF between the two Nb3 Sn
coils. The overall dimensions of the coil, complete with any case or
cryostat in which it may be mounted, but excluding its leads and any
coolant connections to the coil., shall not exceed:
Outside Radius !! 48.34 cm (to be confirmed)
Inside Radius
=_ 18.49 cm (to be confirmed)
Axial Length
t- 20.32 cm (to be confirmed)
4.
11
-7'
t
MECHANICAL INTERFACE
The arrangement of the HFTF coils with and without the test coil is
shown on Drawing AAA-79-104494-00. All dimensions are nominal at this
stage of the design. When the design of HFTF is frozen, final dimensions
together with tolerances will be specified.
4.1 The HFTF is designed so that the magnetic forces on its coils are
self-contained and are not transmitted to the test coil. There will be a
small deflection of the thick end plates bounding the space for the test
coil resulting from the axial forces on the HFTF Nb3 Sn coils. This
deflection will be less than 0.050 inch.
99
4.2
The test coil is located radially by being a sliding fit
over the
inner compression ring.
4.3 The test coil will be positioned axially by the thick end plates
which are attracted towards each other by the magnetic forces on the
Nb3 Sn coils and which are restrained by the inner and outer compression
rings. Some adjustment, by shimming either the test coil or the
compression rings, can be accommodated.
5.
ELECTRICAL INTERFACE
5.1 Coil Insulation Test. The coil shall be fully insulated from its
case and shall withstand a test of 500 V dc for one minute. During this
test, any diagnostics attached to the conductor, such as heaters, strain
gages, etc., shall be connected to the coil; any diagnostics attached to
the case, such as helium level and temperature sensors, etc., shall be
connected to the case during this test.
5.2 Main Current Leads.
Two 15 kA vapor-cooled leads will be provided
by the Facility to carry the current to the test coil.
The interface
will take place at the low-temperature end of the vapor-cooled lead,
where a bolted connection will be made to the leads from the test coil.
Details of the interface to be specified later.
The leads from the coil to the interface will be such that, when
carrying full current, the temperature at the interface shall not exceed
10 K.
5.3
Auxiliary Leads
5.3.1
The Facility will provide the following diagnostic leads,
terminating at panels in the region of the liquid helium level,
which will be the interface with the diagnostic leads from the coil:
5.3.1.1 Thirty heater channels, each two leads, untwisted,
unshielded. Rating, - 25 A pulse.
5.3.1.2 Ninety shielded, twisted pairs for voltage taps; 600 volt
rating (1000 V test) between wires and to ground.
5.3.1.3
Twelve triple shielded leads for strain gages.
5.3.1.4
Six four-conductor leads for thermometers, etc.
5.3.2
Diagnostic leads from the test coil shall be securely
anchored and suitably labelled by the fabricator 'and be not less
than the length to be specified.
6.
DIAGNOSTIC EQUIPMENT
6.1 One power supply is available for energizing heaters or small pulse
coils. The output voltage can be controlled from 0 to 120 V an~d te
maximum current is 50 A. The output is square wave with the time
100-
IZ~T pza..
'2tcv A
controllable from 1 mec to 1 sec.
The unit can be switched to any
number ofV30 parallel channels.
6.2 Twenty B&F signal conditioners capable of operating in either
constant current or constant voltage mode.
6.3
Maximum Current
= 150 mA
Maximum Voltage
=
300 V
A modcomp 1,300 wide range A/D System is available for data
acquisition and analysis.
Total number of channels (including those for HFTF)
=
104.
Maximum Sampling Rate = 300/channel/sec.
Voltage Range
=-5 mV to L10 V (automatic range gains)
Up to 48 channels can be routed via Preston amplifiers-approximately 30 channels available for test coil.
Maximum Common Mode Voltage = 1000 V
Maximum Input = 10 V
A further 56 channels are available, not through amplifiers, but
through relays, to isolate the diagnostics in the event of a quench
in any of the coils, ie., either the test coil or HFTF--approximately
30 channels available for test coil.
Honeywell 18-Channel U/V Recorder
Biomation 4-Channel Analogue Recorder;
Variable Rate,
1000 Samples/
Channel
7.
THERMAL INTERFACE
The HFTF operates submerged in liquid helium at nominal atmospheric
pressure, approximately 4.3 K.
Pool-boiling test coils, designed to
operate in these conditions, may be supplied as open-type coils.
Coils designed to operate at pressures or temperatures other than
7.1
these must supply the coil, sealed in its own case, complete with any
thermal insulation that may be required. In these instances, the
supplier must also provide all equipment and coolant interconnections to
enable the coil to operate under the designed conditions.
8.0
MAGNETIC INTERFACE
The coil data given on SK-1000 can be used for calculating the
magnetic field on the test coil.
The dimensions and average current
density given in this table for the test coil (number seven) are nominal
value and should be replaced by actual values.
101
9.0
QUENCH PROTECTION
The HFTF coils are energized and discharged in pairs to maintain
symmetry about the center line. The inner Nb-Ti coils (Nos. 1 and 3),
the outer Nb-Ti coils (Nos. 2 and 4), and the Nb3 Sn coils (Nos. 5
and 6) are discharged through center-point-grounded resistors.
9.1
The inductance matrix for the coil system is given in Table I.
9.2
The values of the protective resistors are given in Table II.
9.3
A value of 0.002 ohms is proposed for the protective resistor for
the test coil; the maximum voltage generated at 20 kA is, therefore,
40 volts. In this case, one end of the resistor will be earthed and the
circuit will be interrupted by a single-pole circuit breaker.
9.4 LLL has a QUENCH computer program, which calculates the approximate
discharge characteristics of the complete coil system during a quench or
a trip (circuit breakers opened, but no quench). Figures 2A, B, C, etc.
indicate typical performance; other cases can be computed on request.
102
A\A ci'.
71
go-
TABLE I
Inductance Matrix for Coil System
M(1, 1)
= 8.48
M(1,2)
= 3.87
M(2,2)
=
5.16
M( 1, 3) , 3.46
M(2,3) * 1.43
M(3,3)
* 1.43
M(2,4) = 6.39
M(3,4) = 3. 87
=0. 15
M(3,5)
M(l, 4)
= 0.31
M(1,6) = 0.147
M(1,5)
M(1,7) = 0.06
Note:
Coil No.
M(2,5) = 0.20
M(2,6)
* 0.06
M(2,7) = 0.026
M(3,6)
= 8.48
=0.31
M(3,7) = 0.06
7 is assumed to have 86 turns,
M(4,4)
=
5.16
M(4,5) = 0. 06
M(4,6) = 0.20
M(4,7) = 0. 026
M(6,7) = 0.0067
= 0.073
M(5,6) = 0.0098
M(5,5)
M(6,6)
= 0.073
M(5,7)
=
0.0067.
M(7,7)
=
0.0042
operating at 10 kA.
Inductance values are in Henrys.
TABLE II
Resistance of Protective Resistors (Ohms)
Coil Number
Resistance
+ 0.4
1 + 3
0.4
2 + 4
0.27 + 0.27
5 + 6
0.02 + 0.02
7
0.002
103
-NO.
4
NO.
NO. 1
3
NO.
2
-T
NO. 6
NO. 5
LNO.
-Z .
7
L
+Z
7
4 1XI-1
XV
IX1
NO.
COIL FORM (CM)
I.D. X O.D.
LENGTH
-i
x
5 CM
--
COIL
N -.
I.D. X O.D.
WINDING (CM)
LENGTH
AMPS
Z SPACE
Cmz
N
100.0
x 177.8
34.29
105.0 x 172.6
26.25
+
2
100.0
x 177.8
27.29
105.0 x 170.0
19.90
+38.70, +58.60
3
L4
100.0
x 177.8
34.29
105.0 x 172.6
26 .25
-34.60,
- 8.35
3200 .0
100.0
x 177.8
27.29
105.0 x 170.0
19.90
-58.60,
-38.70
3200.0
5
37.0
x 100.0
34.96
40.0 x
91.0
24.25
+16.01,
+40.26
3079.0
6
37.0
x 100.0
34.96
40.0 x
91.0
24.25
-40.26,
-16.01
3079.0
T
37-0x- -965---p-0632-
(AL
8.35,
+34.60
3200.0
7
3200.0
E
COIL DATA
TELEPHONE CONFERENCE MEMORANDUM
'NGHOUSE
WCS
FORM
22822 A
DATE
F
INCOMING
Don Cornish
MR.
WITH
COP
OUTGOING
OF THE
MR.
IES
LLL
OF THE
TO:
SUBJECT:
90P0735
-G.0.
c.O.
Jan. 3, 1980
A.
.. JIrbak
A.
Mn-ntnmaru
- ~
(MTT)
Interface specs for 12 T coil with HFTF
TIME
COST
FILE
CHARGE
DETAIL OF CONFERENCE
"
The current density has been reduced in the HFTF coils as a result of more detailed
analysis.
"
"
The nominal current and turns for each coil are as follows:
Outer NbTi (2 and 4)
I = 1200 amp
N = 1793 turns
Inner NbTi ( 1 and 3)
I = 1200 amp
N = 2366 turns
Nb3Sn Coils (5 and 6)
I = 5000 amp
N = 380 turns
Symmetrically opposite coils are connected in series.
The series lead is brought out
of the dewar.
"
There is a separate power supply for each symmetric coil pair and an additional
supply for the 12 T coil itself (4 supplies total).
"
Dump resistors are permanently connected across each power supply.
.C1
DEPT.
Advanced Programs
105
EXT. NO.
(SI GNATURE)
3077
0~
I1,
I ;
*8
0-
&,C,..
rf
0.
.1
*~
P
.6
o.
6
m
-0o
p
~ &T-HIGH FIELD TE5T FACILITY
4 METER DIA.~CRYOSTAT106
4.'
SK-1001
0
'WIejjnouS qN
-(V)
0
-1O
N
0
oN
0
o o)'dwe
coW
0ua
0
N
z
qr-
m
1cn
CL
E~~
0
z
C
~ii
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8.0 APPENDIX 3 - OPERATION OF THE HFTF
On March 28, 1985, J.R. Miller of LLNL issued report UCID-20394 that describes
the assembly and operation of the High Field Test Facility during the MIT 12 Tesla Coil
experiment. It is included here as an archival reference.
111
UCID- 20394
THE OPERATION OF HFTF TO
TEST THE MIT 12 T COIL
JOHN R. MILLER
MARCH 28, 1985
V \z~
V
This is an informal report intended primarily for internal or limited external
distribution. The opinions and conclusions stated are those of the author and
may or may not be those of the Laboratory.
Work performed under the auspices of the U.S. Department of Energy by the
Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
112
THE OPERATION OF HFTF TO TEST THE MIT 12 T COIL
The MIT coil was tested in HFTF
to
a
peak
field of
very
nearly
12
T.
The
accomplishment
is
note
worthy
as
a
demonstration of "reactor relevant" superconductors to high field
in a realistic coil environment.
Just the operation of the
High
Field
Test
Facility
(HFTF)
in
providing
the
necessary test
conditions is also no trivial feat.
This note reports the
work
involved
in testing the MIT 12T coil, with emphasis given to the
test
facility
itself.
Data
specific
to
the
MIT
coil
are
relegated to appendices.
ASSEMBLY OF THE MIT COIL IN HFTF
For inclusion in the HFTF coil set for test, the MIT coil was
by
LLNL
for
fabricated
placed in a steel cannister especially
that purpose.
Dimensions of the cannister are detailed in Fig.
1.
The material was 316 stainless steel.
Its
primary
purpose
NbaSn
sub-coils
of HFTF against the
was
to
support
the
two
tremendous axial centering forces
present during
operation
to
full field.
Figure 2 shows the MIT coil situated in its test
position
in
HFTF.
The
outer
cylindrical wall of the can was
sized to support the total load with adequate safety margin.
The MIT coil is constituted of three double pancakes (denoted
A,B, and C).
The
inter-pancake splices
and
the
two current
terminals
projected
radially outward from the coil, essentially
on the midplane of HFTF.
Space for these
splices was
provided
between the NbTi sub-coils of HFTF by separating them with solid,
50-mm
thick,
steel
blocks.
Electrical
insulation around the
splices and terminals was provided by
shimming
with
strips
of
NEMA G-10
of
various
appropriate thicknesses.
The shims were
also wedged
in
tightly enough
to
provide mechnical
support
against lateral deflection under Lorentz forces.
Vapor cooled current leads rated at 20 kA were purchased from
current to
the MIT coil.
American Magnetics, Inc. to deliver
Buswork between the bottoms of these leads and the coil terminals
was
constructed
of
13x51 mm 2 copper bar'stock, traced with MFNb3Sn composite conductor (surplus from winding
the
HFTF
NbaSn
sub-coils).
Joints
between
the MIT coil and the buswork ends
were soft soldered using 60Sn-4OPb solder and bolted.
Helium at supercritical pressures was delivered
to
the MIT
coil
through
a
heat
exchanger
system
provided by MIT.
The
system consisted of a counterflow heat exchanger located
in
the
dead
space
above
the HFTF coil set and a final heat exchanger
located in the bore of the coil (Fig. 2).
Cryogenic
valves
to
113
select alternate
flow
paths (cf. the schematic of Fig. 3) were
also a part of the package
provided
by
MIT.
Control
of
the
pressure
and
flow
of
the
helium was accomplished in a system
external to the 2 m cryostat consisting of a valve panel,
a
LN 2
flow
a
counter
line,
delivery/return
a
VJ
precoole'r,
temperature
heat exchanger to warm the gas before flow measurement, a
mass
flowmeter,
and temperature sensors and pressure gages at various
points on the flow paths (cf. the schematic of Fig. 4).
COOLDOWN
Cooldown of the HFTF/MIT 12T ensemble was accomplished
using
the Airco refrigerator--at first using only the LN2 precooler for
cooling
power,
then
later starting the turbine when return gas
from
the
cryostat
had
dropped
sufficiently
in
temperature.
Figure
5
displays
the
cooldown
record of the October run and
Figs. 6 and 7
show
that
of the
January
run.
Both
records
emphasize
that
the most
dramatic results were achieved in the
first three days of cooling before the
turbine was
turned
on.
Without
the turbine, the coil temperature was lowered to -100 K.
The temperature was dropped an additional 50 K using the turbine;
but great care, constant attention to the refrigerator controls,
and
three
to four more days were required.
In the January run,
due to delays caused by the data acquisition computer,
the
coil
temperature was
allowed
to warm
back
to
about 100 K before
transferring LHe.
The amount of
liquid
required
to
complete
cooldown
and
fill was not noticebly greater than in the October
run where liquid transfer was begun with
the
coil
temperature
around
60-70
K.
Several days of effort by a 3-5 man crew could
have been saved
by
dispensing
with
the
turbine
for
further
cooldown
and
beginning
immediately to transfer liquid when the
coil temperature reached -100 K.
During the January run, liquid transfer was begun
initially
from
a
4
kl
dewar
borrowed from MIT.
The transfer from this
dewar was relatively slow compared to transfer from our own 10 kl
dewar.
Using the 4 kl dewar in
that
run,
five
hours
elapsed
before
liquid was measureable in the 2 m cryostat.
In another
two hours, the level reached 50 X on the lower probe (see Fig.
8
for
LHe volume in the 2 m cryostat vs. indicated level).
All of
the initial 3 kl in the 4 kl dewar had been transfered
in
those
seven hours.
The
rate
of
dumping
liquid
from
the
4
kl
dewar
was
unnecessarily
slow (-400 1-h-1).
The reason was discovered when
we switched over to transferring
from
the
10
kl
dewar.
The
section
of
transfer
line
that remains in the 2 m cryostat for
either connection was pushed against the bottom of
the
cryostat
leaving
only
a
narrow
slit
for
liquid to escape. When this
situation was corrected the dump rate of liquid from the
storage
114
dewar was increased more than twofold to 980 1-h-1.
HFTF
Some interesting insights to the cryogenic situation in
can
be
gleaned
from the cryostat fill data.
For example, with
the 980 1-h-1 dump
rate,
the
accumulation
rate
in
the
2 m
cryostat was
only
about 600 1-h-1 even when liquid had covered
the coil.
The boiloff rate
at
high
liquid
level
was
later
measured
to
be no
greater
than 180 1-h-1.
This implies that
losses in the transfer line from the 10 kl dewar consume at least
200 1-h-1.
To put this in perspective,
it
should
be
realized
that
if we tried to maintain constant level in the 2 m cryostat
by throttling the flow through this line, it would
be
necessary
to
use about
380 1-h-1 from the storage dewar just to maintain
level in the 2 m cryostat.
The transfer line
losses
should be
reduced;
if
they
cannot
be reduced, only very rapid transfers
should be considered.
The rate of liquid consumption is not the same at all
levels.
in
the
2 m
cryostat.
As much
quantitative
information as
possible was extracted from strip chart records of the LHe
level
during
these
runs.
The essence of these records as they relate
9
and
10.
Figs.
to variation in boil off rate is displayed in
There are elements of chronology that influece these records (for
example,
time
since the previous fill, the proximity in time to
an event that drastically changed the boil off rate, etc.) but on
the whole they are relatively consistent.
It can
be said
at
least
that
when the level is very low on the coil (after having
been full) the rate of liquid consumption
drops
to -40
1-h-1.
When
the
cryostat
is
very
full (in.the range needed for safe
operation), the boiloff rate rises to as high as 180 1-h-1.
The
magnitude
and
variation
of
the
rate
of
consumption
can be
explained in part (but not entirely) in terms of conduction
down
the
inner
wall of the 2 m cryostat, which is nearly 5-mm thick.
I suspect the foam plug as a virtual heat leak that contributes a
significant heat load for any
practical
test
period.
Careful
thought
should be
given
to
redesign
of
the
portion- of the
cryostat above the coil, because a boiloff rate of
70-80
1-h- 1 ,
limited mainly
by
the
vapor
cooled
lead
losses,
should be
achieveable.
PRELIMINARY ELECTRICAL TESTS
In the October run, coil testing was delayed initially due to
an error in electrically connecting the
seven
individual
coils
constituting
HFTF
and
the
MIT
12
T
test
coil
so that all
contributed in the
same
field
direction.
The
error occurred
because of a simple labeling mistake on the power supply leads to
the six HFTF subcoils.
The mistake was not discovered previously
in
tests
of
the HFTF coil set alone because it was, of course,
not important until another
coil
was
included.
However,
the
115
discovery
of
the error, and the seriousness of the consequences
had it notbeen discovered, emphasize the importance of seemingly
mundane and redundant checking
before operating
so
complex
a
system.
Because of this delay, the first period of testing during the
October run was confined to check-out of the electrical equipment
(power supplies, breakers, etc.)
and
the
cryogenic
electrical
joints.
MIT coil joint resistances are reported in a memo from
M.O. Hoenig attached as Appendix A.
Pertinent
comments
to the
Hoenig memo
are
included
in
a letter from myself attached as
Appendix B.
In addition to these measurements, we determined the
total resistance of the buswork (including all joints) connecting
the MIT coil to the 20 kA vapor cooled leads.
The
resistances,
constant
vs. current and time at all current levels up to the 15
kA used for measurement, were 0.13 micro-ohm for the negative bus
and 0.083 micro-ohm for the positive bus.
At
full
current
(20
kA)
a
heat
load of 85 W (117 1-h-1) would result.
This should
not be considered good performance, but since the
load
was
not
large
compared
to
other
loads
(180
l-h-1
standby at
safe
operating level) and temporary (only present at full current), it
was acceptable.
COIL TESTING
Actual testing of the MIT 12 T coil at full current and field
was carried out during only three days of the October and January
runs (October 30 and January 28 and 29).
The
October
test was
foreshortened by leaks in the MIT cryogenic package.
The January
run was halted by failures of two of the three induction heating
pulse coils required for stability testing in the MIT coil.
In
spite
of these obstacles, which prevented full completion of the
proposed test plan,
a
great
deal
of
useful
information
and
experience
was
obtained--information that will be invaluable in
designing and building future coils with conductors of this type.
RESULTS
and
Results of the October test are included in Appendices A
The results of the January tests are
already mentioned.
B
as
Cambridge,
being prepared for presentation at the 1985 CEC/ICMC,
The following qualitative conclusions can be drawn from the
MA.
potential
results: (1) The cable-in-conduit conductor provides a
means of obtaining high current densities at high fields. (2) The
conductor
provides a means of taking advantage
cable-in-conduit
the
removal
of
of
NbsSn
in
of the high critical temperature
steady
heat
loads
to
the
conductor.
(3)
The mechanical
cable-ininteraction of the conductor cable and the sheath in a
that
must
be
eventually
is
a
subtle
phenomenon
conduit
conductor
sorted out in
order
to
take
advantage
of
the
sheath
as
a
116
in a coil design. (4) The stability of the
component
structural
a
in
perturbations
against external
conductor
cable-in-conduit
realistic coil environment was demonstrated to be quite high.
PROBLEMS EXPERIENCED IN THE OPERATION OF THE 2 M CRYOSTAT
Too often, only those things that went right in an experiment
rosy
a
find their way into a report, and posterity is left with
type
the
of
tests
Since
picture that may be pleasant but unreal.
our
in
times
many
repeated
be
must
report
this
in
discussed
problems
the
of
account
an
future,
near
the
laboratory in
in the execution of these tests will be very useful.
experienced
already
Some of the operational difficulties have been mentioned
is a
following
The
the course of reporting the test results.
in
be
ordinarily
more complete list of problems--the kind that would
most
In
forgotten, at least until the next time they occurred.
cases I try to suggest a possible prevention for future runs.
Loss of vacuum in cryostat
acket
m
2
the
vacuum, in
run,
October
During cooldown for the
The
(to about 10-3 torr).
badly
jacket deteriorated
cryostat
into
feedthru
primary cause was eventually determined to be the
intermediate
the
to
LN2
delivers
that
space
vacuum
the
copper
a
to
A soft solder joint
temperature radiation shield.
feedthru cracked under thermally induced
the
constituting
tube
The crack was repaired using Wood's metal so as not to
stresses.
was
system
(the
make the leak larger while trying to repair it
The repair was sufficient
under vacuum during the repair).
left
test was
the
after
but
for completion of the first test run,
heater
nearby
a
up,
warm
to
allowed
was
line
the
and
completed
melted
seal)
0-ring
an
of
freezing
the
prevent
to
there
(located
Another repair
Wood's metal and recreated the vacuum leak.
the
during
failed
too
it
but
solder,
Sn-Pb
with
time
was made, this
leak
the
and
warmed
was
line
the
time
This
run.
the January
epoxy.
repaired with a filled
with a
replaced
be
It should
The feedthru design is bad.
careful
and
joints
brazed
or
welded
only
utilizes
that
design
induced
thermally
of
relief
the
to
paid
be
attention should
stresses.
Leak in the LN2 baffle of the cryostat vacuum system
diffusion pump
In the search for the leak just mentioned, a less severe leak
vacuum
cryostat
2 m
the
on
was found in the pumping system
as
identified
was
pump
diffusion
the
on
LN2 baffle
The
jacket.
had
baffle
the
in
reservoir
LN2
The
the source of the problem.
to
due
either
supports,
its mechanical
from
loose
cracked
117
vibration or rough
treatment
during
storage
or
installation,
leaving
a. small
leak.
The baffle was replaced for these runs
with a straight spool piece.
The
baffle
leak was
apparently
present before
the more
serious, feedthru leak occurred.
For
when the system was put back on
line after
both
repairs,
the
vacuum
was an
order of magnitude better than before the vacuum
considered
However, this "fix" should only be
failure occurred.
temporary and a proper baffle should be replaced in the system.
Failure of shaft seals and belts on cryostat vacuum
system
fore
As is often the case, when a system failure occurs there are
more
than
one
or two contributing factors, all masquerading as
the major problem.
In the search for the
problem,
it
is
also
unusual
to
discover
all
these factors the first time through.
The above mentioned
vacuum
failure
is
a
prime
example.
In
addition
to
the
two
leaks already described, it also happened
that the foreline vacuum pump failed.
Apparently a shaft bearing
failed causing a shaft seal to leak and reduce the performance of
the pump.
The problem was discovered only because
the
wobbling
shaft
also
caused the drive belts to wear and become loose. All
future runs in HFTF should be preceded by a
thorough
inspection
of
the
various
components of the vacuum system. This system. is
typically run continuously whether the cryostat is in use or not,
and components can
be on
the verge
of
failure without
the
operators' knowledge.
Remote JT valve operator malfunction
the
10
The Airco refrigerator has remote JT valves for both
These have quite different
kl
dewar
and
for the 2 m cryostat.
valve operators attached.
The positioner on the 10 kl
dewar
is
air
operated
and
that
on
the
2 m cryostat delivery tube is
turns
a
nut
that
The motor
operated by an electric motor.
The shaft in turn transmits
a
screw afixed to a shaft.
engages
To do this, the screw must
linear motion to the JT valve needle.
constraint
had
In the past, this
be constrained from rotating.
provided by means of a projection that also indicated valve
been
However, this projection had
position by moving a potentiometer.
some manner.
in
been removed when the potentiometer had failed
Since
its
removal,
only the combination of a freely moving nut
and a relatively tight shaft seal had provided
some measure
of
rotary/longitudinal motion
conversion.
The position of the JT
valve, recorded as turns of the drive nut, must have been a
very
imprecisely known quantity under such conditions.
I recommend
that
the motor driven
valve
positioner
be
replaced with
an air operated positioner like the one on the 10
kl dewar and
that
the
controls
for
the
two
positioners
be
118
consolidated.
Malfunction of LN2 autofill system for Airco precooler/absorber
Airco
the
The autofill system for the precooler/absorber in
refrigerator
cold
box failed to operate during the October run.
or
stopping when
filling
We were able to continue by manually
external signjs (absence or presence of frost on particular pipes)
indicated that
the heat exchanger reservoir was either empty or
overflowing.
However,
this
procedure
resulted
in
extremely
excessive
LN2
consumption,
and
probably suboptimal cooling at
times also.
The problem has
since
been
attributed
to
faulty
contacts
in
a cable connector associated with the level sensors
and corrected.
The
autofill
system
was operational
for
the
January run.
Freeze-ups of the Airco refrigerator
The 2 m cryostat is an inherently "dirty" system that
cannot
up" no matter how great the effort (the
be completely
"cleaned
greatly
to
this
foam plug above the coil stack must contribute
Thus
some "freeze-ups" of the refrigerator cold box,
problem).
be
the
2 m
cryostat,
should
operating
directly
into
when
turbine
run,
however,
three
During
the
January
expected.
four days.
failures caused by icing occurred within a period of
All the failures occurred after coil temperature was below 100 K,
was below 60 K.
The
the
coil
temperature
two
occurred when
should
all
typical impurities causing freeze-up (air and water)
have
been
frozen out in the 2 m cryostat at these temperatures.
dirty
Some other evidence indicates that the purifiers and not a
the main
problem
by
allowing
2 m
cryostat may
have
been
sketchy
at
Details
are
impurities (mostly Na and 02) through.
this
time
but
the performance of these purifiers bears careful
also
Frequent freeze-ups may
investigation before future runs.
be avoided by using the Airco only for precooling to around 100 K
as suggested earlier, without starting the turbine at all.
Deficiency and failure of He gas recovery compressors
during
the
and
once
Several times during the October run,
January
run,
the
helium
gas recovery bags had to be vented to
atmosphere because they overfilled.
The recovery compressors had
been incapable of keeping up
with
the boiloff
from
the
2 m
cryostat.
In the October run only one compressor was available,
the 125 hp Worthington, and it failed during the
run.
For
the
January run,
the
75
hp Worthington
was operational.
Both
compressors were run continuously to maintain
adequate
recovery
speed.
The two together are sufficient, but care must constantly
be
taken to keep one bag nearly empty, especially during initial
filling of the 2 m cryostat when huge quantities of gas are being
119
generated.
It is essential that both be operable before
a
run.
Obviously,- reducing
the
cryostat
losses would
also ease the
burden of reliability and of operating at peak
performance
from
these compressors.
Difficulty in rapidly dumping He xas when recovery bacs fill
For the October run, the recovery bags could only
be
dumped
manually
in
the
event of
and
overfill.
This resulted in a
dangerous situation.
In
the
present
configuration,
when
the
recovery
bags
fill completely, an inlet valve shuts and all gas
flow stops, including flow out of the vapor cooled
leads,
which
could
easily result in lead burn-out and magnet failure.
Before
the Jan.uary run, emergency, electrical operators were
installed
on
the
dump
valves
near
the
lead
flow-meters
to allow the
operator to act quickly to dump the bags instead of having to run
outside to the vent valves in the event of an overfill.
In
the
future, this operation should also be alarmed and automated.
"Malfunction" of JT valve positioner on 10 kl dewar
The pneumatic positioner on the JT valve for the 10 kl
dewar
is
an ancient unit, but still sophisticated and stone- reliable.
However, two associated
a
human
components,
operator
and
an
instrument-air supply
hose,
caused minor
problems during the
October run.
Once, the mechanical lever that closes the feedback
tripped
positioner
circuitry
was
loop
in
the
pneumatic
In
(literally), and once a leak was found in an air supply hose.
both
cases
the
valve and positioner were wrongfully accused of
giving deficient service.
My advice is, "If the 10 kl
JT
valve
is not working properly for some reason, look elsewhere first."
Loss of vacuum in VJ return from 2 m
cryostat to Airco
The vacuum jacketed return line from the 2 m cryostat to
the
Airco
cold
box
frosted
during the
October run.
No leak was
found.
The line was pumped overnight with a mechanical pump
and
put back into service.
It would be wise to routinely pump all VJ
lines that carry LHe before any extended run.
Unexpectedly high boil off rate in 2 m cryostat
both
the
October
The unduly high consumption of LHe during
several times.
already
been mentioned
has
and
January runs
Cryogenic
is
fully warranted.
attention
However, I feel the
the single most serious problem with
currently
is
inefficiency
in
so many
operational
difficulties
HFTF because it presents
ways:
the losses far exceed our current refrigeration
different
of
future
refrigeration
expectations
or
reasonable
capacity
capacity;
they
deplete
our
present
14 kl storage capacity in
120
qvertaxes
gas
intolerab-ly short periods; the rapid evolution of
also
our
capablities to
(possibly
our
recovery capabilities
maintain gas purity); and since none of the cooling power of this
excess boiloff is being utilized, handling of the extremely
cold
effluent
causes problems with maintaining leak tightness of the
entire cryostat and recovery system.
The list could go on,
but
it
is
already
long
enough
to
the
reasonable
person that solutions must be found if
convince
two
possible
tool.
I
suspect
HFTF is to be a
truly
useful
sources of
the heat:
conduction down the inner wall of the 2 m
cryostat has already been alluded to, but
the
virtual
leak
of
heat -slowly being conducted out of the huge foam plug above the
coil stack must also be considered.
My personal opinion is
that
the
foam
plug
offers
no
advantages
over
a system of baffle
plates, and several disadvantages.
There is some support in
the
literature
for my
opinions,
but
they
are mostly couched in
personal experience and the dislike of
such
a
huge
source
of
contamination
in a cryogenic system.
Metal baffle plates result
in a much cleaner system and offer the
opportunity
of
actively
controlled
cooling
by
having
them traced with a tube, through
which
a
metered
flow
of
cold
gas
can
be
extracted
(the
performance
of
the
plates as a radiation baffle is improved by
having a portion of
the
heat
they
intercept
transmitted
to
exitting
gas
rather
than
liquid in the bath).
The boiloff is
thereby reduced and the gas that is
evolved
is
warmed
in
the
process to a temperature that makes it easier to handle.
The baffle plates could also be put in good
thermal
contact
with
the upper portion of the vessel inner wall to allow much of
that
conduction
heat
load to
be
intercepted
also.
The
opportunity
exists to reduce the wall conduction heat load by a
factor of 1/35, making it negligible in comparison to
the
vapor
cooled
lead
losses.
The
plates could be made economically of
aluminum with a tracer tube
welded
on.
Good
contact
to
the
vessel
wall
could be obtained by sectioning the plates to allow
them to be cammed out against the cryostat wall after the magnet
is lowered in place.
Consideration should also be
given
to
opening
the
vacuum
jacket of the 2 m cryostat and modifying the LN2 tracer tubing on
by providing a.section that encircles the inner wall
the
shield
and makes good thermal contact to it at the appropriate
distance
from the top.
Auxillary fill line impropery positioned in 2 m
cryostat
An auxillary fill line was used in the October run
to
allow
LHe
transfer
initially
from several 500 1 dewars.
The thought
was to precool the cryostat with the 500 1 dewars
and
save
all
121
the liquid in the 10 kl dewar for a single uninterupted run.
The
auxilaary -fill
line did not, however, extend deeply enough into
the cryostat to guide the flow underneath the coil stack where it
was needed for efficient cooling.
In fact it was
later
learned
that
it
did
not
even extend below the foam plug.
In spite of
this, some cooling was obtained from the five or so small
dewars
used,
but
nothing
like
their
potential
cooling capacity was
obtained.
The importance of
knowing
the
routing
of
all
the
various
lines
penetrating
the
top
plate before lowering the
magnet system into the cryostat cannot be over emphasized.
Gas leaks in top of 2 m cryostat
In the January run alone, the gas equivalent
of
6000
1
of
liquid was
lost. Much of this loss was due to leaks in the top
plate of the 2 m cryostat (predominantly around the vapor
cooled
leads and in the VCL boxes).
The leaks were tolerable before the
run,
but
got much worse during it because of the excessive flow
of cold gas associated with the unexpectedly high
boiloff
rate.
Nevertheless,
the
sources
of these leaks must be eliminated by
redesign of the lead and lead-box seals before future runs.
A full blown leak
test
of
the
low
pressure
portion
of
the
facility
(2 m cryostat and all recovery lines) is also in order.
The test could be
accomplished
while
the
system
is warm
by
carrying
out
a pressure .ecay test extending over several days.
Reduction of the liquid consumption in the cryostat will
ensure
the reliabilty
of whatever seal
modifications
are made by
eliminating undue thermal stresses on them.
CONCLUSIONS
HFTF
coil
The
The MIT/LLNL 12 T test was extremely useful.
set itself operated faultlessly, unperturbed by the variations of
field,
temperature,
etc.
necessary
to
provide
the
test
it.
It
will
be
an
extremely
environment for the MIT coil inside
tool
for future such testing, unduplicated in many ways,
useful
also
gained
crew
The operations
anywhere else in the world.
In
testing.
in
future
invaluable
be
that
will
experience
is
general, the entire facility, including the cryogenic system,
details that
can be, and for
but
there
are many
excellent;
efficient operation must be, corrected.
122
FIGURE CAPTIONS
Figure 1.
Cannister for containing the MIT 12 T
HFTF.
Figure 2.
Elevation view showing the MIT 12 T coil and the
cryogenic package in HFTF.
Figure 3.
Schematic of the flow circuit of the MIT 12 T coil and
the cryogenic package inside the 2 m cryostat.
Figure
Schematic of the flow measurement/control panel
located outside the 2 m cryostat.
4.
coil
inside
Figure 5.
Record of the cooldown of the HFTF/MIT coil assembly
for the October run.
Figure 6.
Record of the cooldown for the January run ( first
days).
Figure 7.
Record of the cooldown for the January run
(continuation).
Figure 8.
Estimated volume of LHe in the 2 m
indicated level.
Figure 9.
Measured standby boil-off rate vs. level in the upper
range.
The cryostat was previously full.
Figure 10.
Measured standby boil-off rate vs. level in the lower
range.
The cryostat was previously full.
123
six
cryostat vs.
Upper cover plate
Inner compression ring
Test coil assembly
f
f
Outer compression ring
-Lower cover plate
Exploded assembly of test coil and coil case.
124
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October cooldown--MIT 12 T Test
300
250
200
E
150
0
100
50
0
0
1
23
4
56
day
0 vacuum leak
X start turbine
128
+ temporary shutdown
7
January Cooldown--MIT 12 T Test
300-
250
200
d- 150-
E
0
100-
50-
o
0
1
2
3
day
129
4
5
January Cooldown--MIT 12 T Test
120
100-
80
E
-
60-
0
40-
20
-
0
I
5
6
-
____
7
89
day
X restart turbine
0 turbine failure
7
130
10
11
2 m cryostat liquid fill vs. level
3000
I
2500
2000
75
1500
D
.2
1000
500
0
U
ZD
75
100
125
50
liquid level (z of probe height)
It'
150
175
200
Standby boiloff va level (upper)
180
150
120
90
00
60
130
0
30
0
0
20
0 after coil dump 1/28/85
40
60
level (z upper probe)
A before test 1/28/85
132
80
IC10
0 during run 10/25/84
Standby boiloff vs level (lower)
100-
I
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80.1
0
60
-c
N
0
N
-v
40-
0
9TM
0
10
n0E
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0
03
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20
0.
0
20
40
60
level (z of lower pr obe)
I
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133
80
100