CRYOGENIC TEST OF THE PoP DQWCC AT CERN
Experience in preparing and cryo-testing
the PoP DQWCC at BNL
S. Verdú-Andrés, LARP Toohig Fellow
Brookhaven National Laboratory
Crab cavities for LHC
Potential benefits from crabs:
 Luminosity increase
 Luminosity levelling
 Alleviate pile-up
LHC Crab Cavities
2-cavity module
SPS test
4 cavities/IP/side/beam
Between D2 and Q4
 Need 32 crab cavities
Phases of the LHC Crab Cavities project
Today
SPS Test
Final Implementation
LHC crab cavity program phases:
2003  2008 Conceptual design, feasibility study and system development
2009  2014 Proof of Principle Cavities
2014  2018 Cavities and Cryomodules for a validation test in the SPS
2017  2023 HL-LHC system
The PoP DQWCC
…and stiffening frame
Electric field
Magnetic field
PoP DQWCC history
Bulk and light BCP
Light BCP
600°C bake for 10 h
BNL - Test II
BNL - Test I
120°C bake
CERN - Test III
Light BCP
BNL insert
Port assembly
Diagnostics for BNL Test II
#1
#5
Top
#4
#2
PU
FPC
TEMPERATURE MONITORING
Number: 6 thermosensors
Type:
CX-1050
Assembly: EPOXY plus kapton tape
#1 On top of the upper large port
flange (niobium flange)
#2 On FPC port pipe
#3 On inner ring of cavity dome
#3
#4 On PU port pipe
#5 On the pipe of the upper small
port at the 4-port side (flange
with copper disk)
4-port
side
Vacuum
Bottom
#6
#6 On top of the lower large port
flange (niobium flange)
Timeline
CAVITY PREPARATION (about 2 days)
• Wipe cavity with ethanol in buffer area and move into class 10,000 cleanroom.
• The next day, check particle counting. If OK, then wipe cavity with ethanol and move into class 100
cleanroom (ISO 5)
• The next day, check particle counting. If OK, then cavity ready for opening ports.
PORT ASSEMBLY (about 1 day)
• FPC, PU, particle trap and blank-off flanges in class 100 cleanroom
CAVITY ASSEMBLY INTO INSERT (about 1 day)
• Cavity into insert
• Connect vacuum line in class 100 cleanroom
SLOW PUMPING WITH NEEDLE VALVE (overnigth), TURBO PUMP (half day), LEAK CHECK + RGA, ION PUMP
(overnight)
• Class 100 cleanroom
DIAGNOSTICS INSTALLATION (about 1 day)
TOP PLATE RIGGING INTO DEWAR AND ROLLING DEWAR INTO TEST BUNKER (about 1 day)
CONNECT RF CABLING (CALIBRATION, TIME DOMAIN REFLECTOMETRY) AND CRYO LINE (about 1 day)
COOLDOWN TO 4.5K (~)
COOLDOWN TO 2.0K (~)
TEST (about 3 days)
Measurements and Results
 Q0 at around 3~4.5e9.
 In CW mode, temperature of
beam pipe flanges increase.
 Reached 4.5MV kick in
pulsed mode, limited by
quench, consistent with
conditioning test.
 Temperature increase on
pickup port blending area.
 Quench field at ~110mT, with
peak E field at 52.8MV/m
 𝑅𝑟𝑒𝑠 : ~18.3nΩ
Measurements and Results
Lorentz detuning (df/dVdefl)  freq = f(V)
-206 Hz/(MV)^2 from CW measurement at 2K
Pressure sensitivity (dp(=dT)/df)  freq = f(Tbath=p)
-336 Hz/Torr
from low power measurement during cooldown from 4.2K to 2K
Measurements and Results
Residual surface resistance 𝑅𝑟𝑒𝑠 : ~18.3nΩ
Cavity status
BNL cadeau arrives at CERN
on July 10, 2014
•
•
PoP DQWCC and its stiffening
frame in bldg 252-R-003 now
Sealed with stainless-steel flanges* after light BCP at Argonne in May 2014.
Cavity is equipped with its own stiffening frame.
* BNL property, to be shipped back to BNL inside transportation box.
CERN Test III
PoP DQWCC test at CERN - objectives
• Test all the candidate crab cavities on the same baseline.
• Prepare CERN test facility for future SPS cavity tests.
• Quench in Nb-coated DN100CF flanges?
Freshly Nb-coated flanges may lead to better performances.
• Plus evaluate technology for SPS DQWCC
e.g. tuning system
CERN Test III
Test program for PoP DQWCC at CERN
1st
2nd
3rd
– fixed FPC
(vertical test)
– movable FPC
(vertical test)
– SPS tuning system (horizontal test)
Fixed FPC (bolts)
CERN FPC actuator
based on BNL design
CERN Insert
Type I
CERN Test III
Cavity assembly - ports
#
FUNCTION
CONNECTION
A
blank-off
solid DN100 – nonstandard port
B
FPC
FPC actuator system
C
blank-off
solid DN40
D
blank-off
solid DN40
E
PU
PU feedthru DN40
F
vacuum
DN10040 and
valve
G
blank-off
solid DN40
H
blank-off
solid DN40
Clean assembly – BNL class 100 cleanroom
Stiffening frame wrapped
in plastic to reduce
contamination
Port assembly
on wire table
CERN Insert – SPL type
Bottom plate a’ la SPL
 leak test in cleanroom
CERN Insert
Type SPL
Fixed FPC - bellow length for critical coupling?
Facts:
Critical coupling (b=1) depends on:
 Q0, given by cavity performance
 Qext, given by FPC settings
Impossible to predict Q0 beforehand
Overcoupled (b>1) structure preferred
as lower power requirement
bellow length
Strategy:
From 2nd cryo test at BNL, Q0 ~ 4e9.
After light BCP at ANL, better performances expected: Q0 > 4e9.
b=>1  Qext slightly lower than expected Q0.
Tuesday, Sept 23 (S. Belomestnykh)
As the FPC is not adjustable,
e.g. set Qext = 4e9 -> d’=21.2mm
set Qext somewhat lower, 3e9 or 2e9,
to help conditioning the cavity.
 Bellow length ~ 27mm.
Remarks:
FPC coupling depends on coupler shape, penetration and orientation.
 Pay special attention during assembly to the coupler orientation.
FPC coupler orientation for fixed FPC
Diagnostics – 6 CERNOX
CX
CX
old PU
FPC
Inner radius of
CX
cavity dome
(highest B-field)
CX
PU
CX
heater
CX
Inner radius of
cavity dome
(highest E-field)?
Or outer radius of
cavity dome…
(high B-field)
Vacuum
Other thermosensors in all these
regions plus in old and new pick
up ports and, if possible, in all
ports (on blended area of cavity
and port plus on flange)
Diagnostics – OSTs
Possible
quenching
regions:
FPC
PU
Possible quenching regions:
beam ports
plate
Possible
quenching
regions:
Cavity dome
FPC
PU
Vacuum
plate
Diagnostics – 3 unidirectional fluxmeters
CERN Test III
Measurements to be performed
• Monitor vacuum level, radiation (field emission and multipacting) during
operation at different field levels
• Q slope (i.e. Q=f(V)) at 4K and 2K
• Q = f(T) for low field level to get residual surface resistance estimation
• Residual magnetic field level and corresponding residual magnetic field
surface resistance
• Lorentz force detuning (df/dVdefl)  freq = f(V)
• Pressure sensitivity (dp(=dT)/df)  freq = f(Tbath=p)
• Determine multipacting regions.
• Radiation spectra
• Magnetic field
CERN Test III
Cavity far from ideal… heat loss
• FPC bellow is not coated (difficult to coat welded flanges).
• Spacing between flanges will let field see SS from flanges and
Cu from gasket.
• FPC and PU hooks made of copper (Nb coating was not
adherent enough on copper surface).
Thanks for your attention
Questions?
Cavity assembly – hardware (I)
PORT
FUNCTION
CONNECTION
BOLT
TYPE
#BOLTS
#NUTS
#WASHERS
A
blank-off
solid DN100
M8x55
x16
x16
x32
B
FPC system
bellow DN40
M6x35
x4
x4
x8
anti-collapse
???
x4
x16
x8
feedthru DN40 M6x35
x4
x4
x8
C
blank-off
solid DN40
M6x35
x6
x6
x12
D
blank-off
solid DN40
M6x35
x6
x6
x12
E
PU
feedthru DN40 M6x35
x6
x6
x12
F
Vacuum: DN10040 DN10040
and valve
valve DN40
M8x55
x16
x16
x32
M6x35
x6
x6
x12
G
blank-off
solid DN40
M6x35
x6
x6
x12
H
blank-off
solid DN40
M6x35
x6
x6
x12
In addition,
• bolts and ¿pins? for stiffening frame in case of magnetic hardware is found
• hardware for the piece on top of the cavity for transportation
Cavity assembly – hardware (II)
BOLT TYPE
# BOLTS
# NUTS
# WASHERS
M8x55
32
32
64
M6x35
48
44
88
16
8
Anti-collapse? 4
Total DN40 copper gaskets:
8
Total DN100 copper gaskets: 2
Remarks:
• all bolts are Ag-coated A4-100 stainless-steel
• apply safety factor of 2--3 when ordering
Cavity assembly – FPC system
Two options:
- Fixed FPC: 1st test
- Movable FPC: 2nd test
Remarks:
FPC coupling depends on coupler shape, penetration and orientation.
 Pay special attention during assembly to the coupler orientation.
FPC actuator
T. Renaglia (CERN)
based on BNL design
Framework – LHC Crab Cavities
If head-on collisions, debris can interact with the machine
 Crossing angle
but decreased peak luminosity
 Crab crossing
reestablish head-on collision for maximal ℒpeak
 Need crab cavities (deflecting cavities in phase 0)
For LHC, need 4 cavities per side per IP per beam…
32 cavities!!!
𝜃𝐶 2
𝜃𝐶 2