1. Development in Russia of Megawatt Power Gyrotrons for Fusion
ITR/1-4Ra
Development in Russia of Megawatt Power Gyrotrons for Fusion
A.G.Litvak1, G.G.Denisov1, V.E.Myasnikov2,
E.M.Tai2,E.V. Sokolov, V.I.Ilin3
1Institute of Applied Physics, Nizhny Novgorod, Russia 2GYCOM Ltd., Nizhny Novgorod, Russia 3Tokamak Physics Institute, Kurchatov Center, Moscow, Russia
Recent results in development of RF gyrotron for ITER
Development of multi-frequency gyrotrons
Recent results in development of JAEA gyrotron for ITER
Summary (ITR/1-4Ra and FTP-1/3Rb)

2. The main specifications of the gyrotrons for ITER are described below:
Item
Specification
Nominal output power
 0.96 MW at MOU output
Nominal frequency
170±0.3 GHz (TBD) including initial transient phase
Pulse length
3600 sec (TBD)
RF power generation efficiency
 50 % (with collector potential depression)
Gaussian content
> 95 % at output waveguide (63.5 mm) of MOU
Power modulation
1 kHz (cathode); 5 kHz (anode)
For more details see Technical specifications (

3. Russian 170 GHz ITER Gyrotron. Design features.
Gyrotron cavity designed for TE mode with specific wall loading 2kW/cm2 at 1MW
Diode type electron gun forms the electron beam with optimal size, up to 50A / 70-80kV
Synthesized Built-in quasi-optical converter .Gaussian mode content over 95% at stray radiation less than 5%
Main output window is based on CVD diamond disk of 106-mm diameter with 88-mm clear aperture.
Relief window uses ceramics (BN or AlN) disk of 123-mm diameter to transmit 40 kW.
Depressed-collector with longitudinal beam sweeping is capable to withstand 1-MW electron beam. Enhances gyrotron efficiency over 50%.
DC break insulator upon cryomagnet top flange. C8F20 fluorocarbon as a coolant .
LHe-free cryomagnet has a bore diameter of 160 mm.
Gyrotron inner surfaces are fabricated from copper with water cooling for CW operation.
Gyrotron total height is 2.7m. Gyrotron weight is about 300+ kg.

4. Achievement of ITER relevant parameters with RF gyrotron
In the last five years four gyrotron prototypes were fabricated and tested.
Gyrotrons V-10, V-11 were tested in 2010 and 2011 respectively with CRYOMAGNETICS LHe –free magnet.
It is important to note that two last gyrotrons (V-10 and V-11) demonstrate very similar output parameters (see Table below).
Gyrotron V-11 at the test
stand in Kurchatov instituite

5. ** Demonstrated serial pulses
Summary of test results attained with V-10 and V-11 gyrotrons
Gyrotron
Beam voltage kV
Beam
current A
Retarding voltage
Power * kW
Efficiency %
Pulse
duration
sec
V-10
V-11 71 70 34
39.5
30.5 30
~750
~850
~54
~53
1000
600 ** 45
31.5
~960
~55
400 (serial pulses)
70.5
* Power measured at MOU output and it is approximately 5% less than gyrotron output power
** Demonstrated serial pulses

6. ITER-relevant repetitive operation
As for a reliability test, 0.8MW/600s shots were requested in every 50 minutes
for 3 days in of April 2011.
Only 3 pulses of 30 were interrupted by some reasons.
Ten pulses were made in presence of IO representatives.
Ub, kV
Urec,
Ib, A
I_m, А
t_req, s
I_g.c
t_pulse, s
Date
Regime
Pulse stop
70,9 30 34
82,65
600
1,5
Operating_800kW
Regular 71
510
Cut-off
70.8
1.5

7. 0.8MW/34A/600s serial pulse of V-10 gyrotron

8. terminal load collector cavity
Calorimetry in the 1MW/1000s pulse for gyrotron V-11:
blue curve- terminal load, pink - collector, green – cavity.

9. Hence the cooling system allows power increase.
Hard structure and intense cooling of a gyrotron cavity provide good stability of operating frequency. Total frequency drift for 1 MW operation slightly exceeds 100MHz.
After ~1.5s frequency is practically stable with very small deviations of about 10MHz.
Hence the cooling system allows power increase.
170 GHz gyrotron, TE25.10
100 MHz

10. 1.2 MW/ 100 s operation of V-11, 170 GHz gyrotron, TE25.10
(1.2 MW at MOU output). Cavity and collector survived in long pulses.
Electron beam
( ) kV
53 A
2300 kW
Calorimeters, kW:
Main load -1150
Pre-load
MOU ( refl.)
Relief wind. - 40
Collector – 1080
 2345

11. TE28.12 mode gyrotron model. 100-µs/5-10Hz tests. OLD & NEW QO CONV.
1.5 MW
CW compatible
Long pulse tests planned for Oct.-Nov. 2012

12. indices at each radial index
IAP RAS
GYCOM
Frequency tuning/switching in MW gyrotrons
One mode
Magnetic field or voltage tuning
Azimuth index change
Magnetic field and voltage optimization
Series of azimuth
indices at each radial index
Typical frequency tuning ~ 0.1%
Typical frequency step 2-3%, 3-4 steps
About 10 steps in 30% frequency range
FADIS
Multi-purpose ECW systems

13. Two- and multi-frequency gyrotrons High-eff. mode converter
IAP RAS
GYCOM
IAP/GYCOM experience in MW power level multi-frequency gyrotrons
Frequency, GHz
Power
Pulse, sec
Note
Two- and multi-frequency gyrotrons
105 / 140 MW 10
4 tubes
delivered to ASDEX-Up
147 / 170
0.7/1.0 MW
0.1
Tested with BN window MW
10-4
Short –pulse mock-up,
6 frequencies,
high-eff. converter
Short-pulse mock-up,
11 frequencies,
BN Brewster window
0.7 – 0.9 MW
0.1 (10)
4 frequencies
High-eff. mode converter
71.5 / 74.8 / 78.1
0.8 MW
3 frequencies, 56% eff.

14. Design requirements for the multi-frequency gyrotron for ASDEX Upgrade
Example:
Design requirements for the multi-frequency gyrotron for ASDEX Upgrade
Frequency range (at least 4 frequencies) 105 – 140 GHz
Output power:
at frequency 140 GHz 1 MW
at frequency 105 GHz MW
at intermediate frequencies 0.8 MW
Pulse duration s
Efficiency with energy recovery %
Output radiation Gaussian beam
7 years of common (with FZK, IPP, IPF) development

15. + ? Multi-frequency gyrotron. Main problems.
IAP RAS
GYCOM
Multi-frequency gyrotron. Main problems.
Effective gyrotron operation at different modes
Effective conversion of all modes into Gaussian beam
Tuneable or broadband window + ?

16. One-disc CVD diamond windows for gyrotrons
Small dielectric loss
e-o thermal conductivity
Widely used for conventional single/double frequency gyrotrons;
1.8 mm thick => 4 half-wavelength at 140 GHz and 3 h-w at 105 GHz

17. POSSIBLE WINDOW TYPES FOR A MULTI-FREQUENCY GYROTRON
Advantage
Drawback
Double- disc
Clear concept
Two discs
Disturbed gyrotron operation due to narrow band of low reflection
Brewster, circular
Wide instant band
High field near the disc
Vacuum duct
Thicker disc
Brewster, elliptical
Simple scheme
Poor transmission characteristics
Corrugated matched surface
Broad instant band
Expensive fabrication
Worse mechanical stability
Travelling wave resonator
Zero reflection
Easy tuning

18. Novel window concept - travelling wave resonator.
IAP RAS
GYCOM
Novel window concept - travelling wave resonator.
(Recollected experiment in & recent FADIS experiments) θ θ
At the resonance frequency kL = 2πq (q = 1, 2, 3…) the reflecting power from the cavity is equal zero:
|R|2 = 0, |T|2 = 1 , |A|2 = 1/t2
Mirror cavity with a traveling wave.
W1 and W2 are CVD diamond disks.
T, R and A are amplitudes of transmitted, reflected and traveling wave beams.

19. IAP RAS
GYCOM
Quality factors of the ring resonator:
~ for FADIS (QFADIS >> Q gyr cavity )
< 500 for the window
Possible trajectories for the window ring cavity and 3D drawing for the second option

20. IAP RAS
GYCOM
Relief window
Calorimetric load
Drawing for the MF gyrotron assembly with window. Standard 106 mm disc.

21. 105 GHz (a), 117 GHz (b), 127GHz (c) and 140 GHz(d) gyrotron operation
IAP RAS
GYCOM
1 MW/10 sec MF gyrotron for ADEX-Upgrade has been fabricated
2-frequency tests in June, 2012 – 0.9 MW/140 GHz; 0.8MW/105 GHz
4 -frequency tests (initial in June 2012 (beam measurements), final in early 2013)
Field structures (wave beam amplitude and phase spatial distributions) for
105 GHz (a), 117 GHz (b), 127GHz (c) and 140 GHz(d) gyrotron operation

22. 170GHz Gyrotron Development in JAEA
TE31,8 mode gyrotron
• 1MW/800s
• 0.8MW/1hr operation
• Max. efficiency: ~60%
• Total output energy:
>250GJ
• For power increase,
higher mode oscillation has been challenging
TE31,11 mode gyrotron (J7)
(Multi-frequency operation, >1.3MW operation )
• 5kHz power modulation is improved
using novel anode switching
170GHz gyrotron

23. Initial experimental results
170GHz / 137GHz (TE31,11/TE25,9)
170GHz high power test
Time [s]
Pressure
Vbody =28.5kV
Vanode=-6.8kV
Vmain =-46kVkV
Ibeam =51.6A
RF(170GHz)
~1.1MW
(45.4%)
Pulse duration : 0.5msec
1.3MW output was demonstrated at both frequencies
Stable 1.1MW / 5s oscillation was obtained.

24. Multi- Frequency Gyrotron
Beam profiles at output window
Experimental Result
Calculation
203GHz GHz GHz GHz
(optional)
(optional)
RF beams of three frequencies pass through
the center of the window.

25. Long Pulse Experiment (170GHz/137GHz)
Time[s]
Time[s]
170GHz / 31,11
0.91MW (75s)
137GHz / TE25,9
0.54 MW (20s)
Long pulse operation was demonstrated at both frequencies
(under conditioning for further performance)

26. 5 kHz power modulation (Single anode switch)
Vbody
Vanode
Vcathode
60sec
Ibeam
ITER target
5kHz/50s
(0.5MW-1MW) mod.
Attained
5kHz/60s
Full 1.1MW mod.
50.5A RF
(1.1MW)
60s
1ms

27. 5kHz Power modulation using double anode switch
Single switch
Time[msec]
Single switch
Double switch
Improved
Vanode-cathode RF
Lower frequency excitation at
start-up phase was improved by
introducing the double anode switch.
Double switch

28. Summary RF
The main ITER requirements to gyrotron performance have been demonstrated: 1MW power, 1000 seconds pulse duration, 53% efficiency. Reliability tests were performed. The gyrotron operation regime of 1.2 MW was found for 100 second pulses. The gyrotron prototype for enhanced power of 1.5 MW was designed, fabricated and successfully tested in short pulses.
Testing of the multi-frequency gyrotron for ASDEX Upgrade with a new tunable window is in progress. Short pulse (0.1 sec) tests showed good operation at chosen four frequencies. Gaussian mode content in the output wave beam is high. In 3 second pulses the gyrotron showed 0.9 MW at 140 GHz and 0.8 MW at 105 GHz. The gyrotron was delivered to ASDEX Upgrade in July 2012 and first tests at the site are planned for October 2012. JA
The dual frequency 170 GHz/137 GHz gyrotron with triode electron gun is successfully
designed and tested. In the short pulse experiments (<1 ms), more than 1.3 MW is
generated for both frequencies. The long pulse experiments show 905 kW/45%/75 s for 170 GHz and 540 kW/42%/20 s for 137 GHz.
The 5 kHz modulation achieves the 1.16MW with 48% electrical efficiency by using the short-circuited switch between the anode and the cathode. In order to improve the rising time of the cathode-anode voltage, the double switch conjuration is introduced.
The fast frequency change by using the SCM with the fast sweeping coil inside the bore for quick magnetic field change is successfully demonstrated. A 3 GHz frequency change is succeeded within 3.5 s.