Experimental results and recent developments on the
EU 2 MW 170 GHz coaxial cavity gyrotron for ITER
S. Kern1, J.-P. Hogge2, S. Alberti2, K. Avramides3, G. Gantenbein1, S. Illy1, J. Jelonnek1, J. Jin1, F. Li2,
I. Gr. Pagonakis1, B. Piosczyk1, T. Rzesnicki1, M. K. Thumm1, I. Tigelis4, M. Q. Tran2
and the whole EU home team at EGYC
KARLSRUHE INSTITUTE OF TECHNOLOGY, Institute for Pulsed Power and Microwave Technology (IHM)
1
Karlsruhe Institute of Technology (KIT), Institute for Pulsed Power and Microwave Technology (IHM), Association EURATOM-KIT, D-76131 Karlsruhe, Germany
de Recherche en Physique des Plasmas (CRPP), Association Euratom-Confédération Suisse,EPFL, CH-1015 Lausanne, Switzerland
3National Technical University of Athens (part of HELLAS), School of Electrical and Computer Engineering, 9 Iroon Polytechniou st., GR15773 Athens, Greece
4National and Kapodistrian University of Athens (part of HELLAS), Faculty of Physics, 157 84 Athens, Greece.
2Centre
European GYrotron Consortium (EGYC)
KIT – University of the State of Baden-Wuerttemberg and
National Research Center of the Helmholtz Association
www.kit.edu
Overview
Introduction
Summary and consequences of former experiments
Design modifications to the industrial CW prototype
Tests of the refurbished CW prototype
SAT and RF test
Post-test evaluations
Experiments with the short pulse pre-prototype
Future plans
2
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Introduction
The EGYC consortium develops under F4E contract 170 GHz
gyrotrons in support of EU’s contribution to ITER’s ECRH system.
- EGYC is currently CRPP, KIT, HELLAS, IFP-CNR.
The industrial partner is Thales Electron Devices (TED).
Until now, the goal was a 2 MW coaxial cavity gyrotron.
Three CW prototypes at increasing pulse length goals (1s/60s/3600s)
foreseen, only one build so far.
A 1 MW conventional tube development as fallback was started 2008.
Due to essential delays, switch to the fallback solution is probable.
This presentation reports on latest results and future plans
for the coaxial cavity project
3
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Summary of former experiments
In 2008 first experiments with CW prototype at CRPP:
Serious problems with the electron gun:
low frequency oscillations (~100 MHz region)
low voltage standoff with magnetic field applied
-> Analysis shows the existence of potential traps in the gun
RF output beam pattern insufficient (77% Gaussian content)
-> Application of new launcher design methods
RF power limited to 1.4 MW in short pulse due to mentioned problems
Power capability of the collector successfully tested (2.2 MW/10s)
Pre-prototype short pulse tests at KIT until end 2008:
Power limitation by limited magnetic field (6.7 T instead of 6.87 T)
-> Application of additional normal conducting (NC) coil
Indications of beam-tunnel oscillations (159 GHz)
-> Application of corrugated beam tunnel
Same RF beam as in prototype
4
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Resulting modifications to the CW prototype
The CW prototype was refurbished with design improvements:
New gun design following improved design rules
New launcher design
Corrugated beam tunnel
Additional modifications in mechanical construction:
Ion getter pumps moved to lower magnetic field
Large ceramic isolator mounting revised for lower force during bakeout
Validation tests with the short pulse pre-prototype at KIT in 2009:
Corrugated beam tunnel applied
-> No parasitic oscillations
New launcher design as above
-> 96 % Gaussian content
Achieving 6.87 T with NC coil
-> operation at nominal parameters
-> nominal operation: 2.2 MW @ 30 % efficiency (w/o depr. collector) !
5
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Mechanical issues with refurbished CW prototype
Refurbishment and modification started in 2009
Manufacturing problems caused massive delays
- some clearly attributed to the attempt to refurbish a large device.
The refurbishment of the mirror box was considered critical by the
manufacturer, after brazings became untight at bakeout. In particular, one RF
absorber had to be removed.
Delivery date moved from summer 2010 to finally end September 2011.
The tube was untight on delivery.
It could be sealed and still showed good vacuum properties after pumping.
Achievable pulse length was unclear then.
After four days of successful RF operation, another RF absorber broke and
flooded the tube with water, terminating any further experiment.
Reasons still have to be investigated in detail,
ultimate cause is accidental operation in wrong mode rotation.
After experiment, additional problems of alignment were found.
6
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
SAT test of the prototype gyrotron
Site acceptance test (SAT) was successful:
Excellent HV stand-off without and with magnetic field
Cooling tests OK
Beam extraction tests OK (58 kV / 75 A after 2 days of conditioning)
Coaxial insert .vs. electron beam alignment OK
Body current higher than expected, but acceptable
Body .vs. electron beam alignment ~OK
(coarse measurement, made in x direction only)
-> The tube was formally accepted. Green light to proceed with RF tests
was given by TED on December 2nd 2011.
7
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
RF tests of the prototype gyrotron (Dec. 5.-9.)
After 4-5 days of RF conditioning,
the tube delivered
2 MW / 170 GHz (short pulse ~1ms)
with an efficiency of 45 %
at 75 A (nominal value) and
90.5 kV (60 kV + 30.5 kV),
(nominal: 90kV, 55kV + 35kV)
No particular optimization,
no evident sign of saturation,
not finally conditioned.
8
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
RF beam pattern of the prototype
Mode TE 34,19
Mode TE 35,19 ?
Logbook shot #10410, 2011-12-05
9
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
RF beam pattern of the prototype
Mode TE 34,19
Simulation
10
08.05.2012
Comparison
pre-prototype 96 % GC
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
refurbished
prototype
Institute for Pulsed Power and
Microwave Technology
RF tests of the prototype gyrotron: Summary
Positive results
2 MW / 170GHz short pulse
efficiency of 45 % (using depressed collector),
non-optimized,
at nominal beam parameters 75 A, 90.5 kV,
depression voltage 30.5 kV (nominal: 35 kV)
Very good RF beam pattern
-> second validation of launcher redesign
No low frequency oscillations
Excellent voltage standoff
-> validation of gun redesign / design principles
No evidence for parasitical RF (160GHz range)
-> nth validation of corrugated beam tunnel
All design modifications were
verified to a high degree !!
11
08.05.2012
Negative results
Unexpected, but acceptable body current
Unclear alignment situation
Absorber broken, total loss of tube
No long pulses were possible !
Unclear observations
Unexpectedly high starting currents (~60 A !)
Tube prone to operation in wrong mode rotation
-> results in high stray radiation
-> ultimate cause for broken internal absorber !
Body current -> compare to pre-prototype tests
These effects could be related to misalignment !
Nevertheless, the risk of total loss of a tube
due to a breaking absorber is inacceptable
-> redesign of internal absorber scheme
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Post-test evaluations: Alignment
The magnet alignment (ASG magnet at CRPP) could only be checked
after the experiment.
Results of subsequent check:
Magnetic axis is shifted by 0.7 mm in y-direction
(check with tube indicating good alignment done in x-direction only !).
Additional result: Due to some loose stabilisation rods, the tube can be
easily bend by millimeters, resulting in basically undefined alignment !
12
->
The relative body-beam alignment along y
could have been anything between good and bad !
->
Investigations on the influence of tube alignment
are needed for evaluation of the observations !
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial cavity gyrotron
Institute for Pulsed Power and
for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Microwave Technology
Experimental setup of the pre-prototype
Experiments with the KIT pre-prototype are currently running in short pulse in the
following configuration:
Further improved launcher design: smoothed launcher surface
Electron gun refurbished by TED:
New emitter ring
New cathode and anode shape, identical to
CW prototype
-> this includes a small halo shield
with ~2mm electron beam clearance
Ready for depressed collector operation
Gyrotron housing reworked
to fit into 220 mm bore hole
-> KIT OI magnet was equipped
with cooled CW NC coil
13
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Alignment procedure and measurements
Shift of the electron beam position using dipole coils
dR/Idipol=0.1mm/A
10
before the alignment
Emission uniformity test and alignment of coaxial insert
5
IXdipol / A
measurement
0
-5
-10
-10
-5
0
5
10
Iy
IYdipol / A
Verification of the gyrotron position
Start / End of
the probe
Concentricity of the coaxial insert
with respect to the electron beam:
δR ~ 0.04mm
Concentricity of the electron beam
with respect to cavity wall:
δR ≤ 0.1 mm
-> excellent alignment conditions
14
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Latest experimental results of the pre-prototype
Current results of the ongoing short-pulse tests are:
RF power:1.9 MW @ 28% efficiency (w/o depr. collector), not optimized
Reduced stray radiation: 4% instead of 7%
Good beam pattern
50
2,0
45
1,8
40
PRF / MW
35
1,4
30
1,2
25
1,0
20
0,8
15
0,6
78
80
82
84
86
88
90
92
UC / kV
15
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
efficiency / %
1,6
Latest experimental results of the pre-prototype
Comparison to CW prototype tests:
Low starting currents (10A)
No unusual danger of operating in wrong rotation
Good voltage standoff
But: strong LF oscillations during startup – due to gun rear part or small
remaining potential traps?
Body current at design parameters
-> can be avoided by parameter settings
-> but calls for investigations: reasons are unclear, halo shield design ?
- electron beam radius appears 1.8 mm larger than expected !
16
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Latest experimental results of the pre-prototype
Next steps:
Further conditioning
Preparation for depressed collector test
Tests of the influence of mislalignment
17
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
New Launcher / q.o. system measurements
The smoothed launcher shows
an equally good RF beam
pattern as its predecessor.
burned
paper
spot
Measured stray radiation is
essentially reduced to
window
4 % of the RF output power
Former results:
7 % original KIT design
5.5 % IAP design
thermal image
85 mm from window
18
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
thermal image
1000 mm from window
Institute for Pulsed Power and
Microwave Technology
Future plans
2nd Industrial CW prototype: formal decision pending, 1MW decision probable
Agreement on necessary modifications on scientific side achieved
In view of their future relevance, KIT will continue experiments with coaxial
cavity gyrotrons – if necessary on stretched time scales.
The KIT short-pulse pre-prototype gyrotron will be sequentially extended for
longer pulse lengths.
This is made possible through a modular approach which enables an easy
exchange of components.
Next experimental steps with this “Modular Gyrotron Concept“:
(1) Test other components in short pulse: ‚
different launchers, modified electron guns, different beam tunnels
(2) Add CW collector and CVD window -> ~100 ms pulse length
(3) Replace remaining short pulse components (cavity,q.o. system, beam tunnel,
gyrotron housing) by cooled CW parts -> 10 s pulse length
In parallel: broad band operation tests (around 140 GHz /1.8MW already done)
19
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Modular gyrotron setup steps
Current step:
First depressed collector tests
Launcher test
CW gun with prototype shape
- cathode nose easily exchangeable
2nd: short pulse component tests
Beam tunnel, launcher, anode shape
3rd: CW collector and window
Increase of pulse length to ~ 100 ms
4th: fully CW compatible
CW cooling added, new RF absorber scheme
New redesigned electron gun
Increase of pulse length up to 10s
(KIT power supply limit)
20
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Plans for a hypothetical 2nd CW prototype
Component,
topic,
observation
Internal
absorbers,
mirror box
Launcher,
Q.o. system
Halo
shield
Collector
Beam
tunnel,
parasitic
modes
Tube
alignment
Modes
with
wrong
rotation
High
starting
currents
High
body
current
Better
cooling
of shaft
Any
other
tube
component
Summary
Changes
Remove and
discuss
replacement:
Preferably two
relief windows
with or without
stainless steel
pipes
Replace the
launcher by
the new
version,
presently
under test
(lower stray
radiation
already
proven)
Increase
halo shield
radius by
0.5-2mm
To be short
term
optimized
No
change
No
change
Revised by
TED;
possibility
for
controlled
alignment
tests added
No
change
No change
No
change
No
change
No
change
Next step
activities
cooled stainless
steel pipes
coated/uncoate
d/inside carbon
tubes
- relief windows
- mirror vessel
partly or totally
coated (CrO,
CR2O3) with
external cooling
21
08.05.2012
Consider
tube
inspection
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Summary
The latest test results with EU 2 MW 170 GHz coaxial cavity tubes
were reported.
CW prototype results:
2 MW / 170 GHz / 45 % non-optimized in very short time
All design modifications validated
No long pulse validation of RF performance or cooling (except collector)
Tube damaged, internal RF absorber scheme needs redesign
Short pulse pre-prototype results:
1.9 MW 28 % (without depressed collector, not finally conditioned)
Smoothed launcher validated: stray radiation reduced to 4 %
Depressed collector operation under preparation
Future plans:
2 MW or 1 MW ITER development: F4E decision pending
Coaxial experiments towards long pulse continue at KIT
22
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology
Acknowledgement
The authors acknowledge gratefully the continuing support of TED and F4E staff in
these projects, in particular F. Albajar, F. Cismondi and T. Bonicelli at F4E as well
as R. Marchesin, C. Lievin, F. Legrande and P. Benin at TED.
This work was supported by Fusion for Energy under Grant F4E-2009-GRT-049
(PMS-H.CD)-01 and within the European Gyrotron Consortium (EGYC). The views
and opinions expressed herein do not necessarily reflect those of the European
Commission. EGYC is a collaboration among CRPP, Switzerland; KIT, Germany;
HELLAS, Greece; IFP-CNR, Italy.
Thank you for your attention !
23
08.05.2012
S. Kern et al., Experimental results and recent developments on the EU 2 MW 170 GHz coaxial
cavity gyrotron for ITER, EC17 Workshop, 07-11 May 2012, Deurne, The Netherlands
Institute for Pulsed Power and
Microwave Technology