Progress in Development of Multi-Frequency High-Power Gyrotron

29aP69

池⽥亮介，⼩⽥靖久，⼩林貴之，梶原健，⾼橋幸司，森⼭伸⼀，坂本慶司

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TE31,11

gyrotron TE31,8

gyrotron

Pow

er r

efle

ctio

n r

ate

[%]

ra

d [

deg.

]

Oscillation frequency [GHz]

19,722,8 25,9

28,10 31,11 34,12 37,13

4 /2 5 /2 6 /23 /2

18,5 35,931,8

27,7

36,9

22,6

Design parameters of JA ITER gyrotron

ITER gyrotron at QST

ITER gyrotron of TE31,8 mode had already achieved 1.0 MW CW operation with total efficiency of 55%. Higher order mode of TE31,11 has been selected to enhance the output power and

to realize multi-frequency oscillations.

Mode TE31,8 TE31,11

Cavity radius Rc = 17.90 mm 20.87 mm

Triode MIG Re = 46.5 mm Same

Beam radius Rb = 9.13 mm Same

Diamondwindow

Dw = 82 mmtw = 1.853 mm

Same

Remark 1MW/55%/800s0.8MW/57%/1hr

Up to 1.4 MWMulti-frequency

Design for multi-frequency oscillation by ITER type gyrotron

Oscillation frequency 104GHz 137GHz 170 GHz 203 GHzCavity Field 4.08 T 5.32 T 6.63 T 7.98 TGun Field 0.172 T 0.21 T 0.28 T 0.31 T

Beam radius 9.25 mm 9.19 mm 9.13 mm 9.10 mmAnode-cathode

voltage28 kV 36k V 42 kV 50 kV

Pitch factor 1.32 1.35 1.35 1.35Oscillation power 1.12 MW 1.26 MW 1.3 MW 1.3 MW

Oscillation efficiency 39% 44% 45% 45%

Oscillation frequency (Cavity mode number)

Transmission efficiency between radiator to window

104GHz (TE19,7) 95.5%

137GHz (TE25,9) 96.9%

170 GHz (TE31,11) 98.5%

203 GHz (TE37,13) 97.6%

(Radiator design was optimized for170 GHz beam.)

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Time [s]

170GHz(1MW)

137GHz(1MW)

104GHz(0.9MW)

Water flow : 8 L/min

DCB absorber

43 kW

29 kW

16 kW

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dow

load

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Time [s]

170GHz(1MW)

137GHz(1MW)

104GHz(0.9MW)

Water flow : 7 L/min

Relief window load

8 kW

14 kW

21 kW

Boiling!

Oscillation efficiencies at the cavity for sub-frequencies were close to one at main designed 170GHz oscillation. Low frequency oscillations are limited due to water temperature at RF absorber.Modification of the radiator design is underway to realize longer pulse 1MW operation (> 30s) at 104 GHz and to

apply the low field experiments (1.8 T) in ITER.

Calculated transmission efficiency from radiator to window is 96.6 %.Cavity heat load reaches 2kW/cm2 at 1 MW cavity power.If the internal loss is ~10 % (203GHz), output power is up to 0.9 MW.

Power balance in gyrotron for quad-frequency oscillations

104 GHz 137 GHz 170 GHz 203 GHz

DCB [%] 6.1  3.9  2.3  2.6 Relief window [%] 2.3  1.4  0.8  0.9 viewing ports [%] 0.6  0.3  0.1  0.1 Diffraction loss [%] 8.9 5.6 3.3  3.7 

Mirrors [%] 0.9  0.7  0.7  0.6 Radiator [%] 2.0  1.8  1.8  1.7 Cavity [%] 2.8  3.0  3.4  3.8 

Ohmic loss [%] 5.7  5.4  5.8  6.1 

Total internal loss [%]

14.6  11.1  9.1 9.7

Output eff. [%] 24.0  26.5  28.0  25.0 Cavity eff. [%] 27.5  29.4 30.5 27.4

x3 x2

JA ITER gyrotron is capable of multi-frequency oscillations with uniform directional beam.

1.2MW power and ~ 50% efficiency have been demonstrated.

Steady-state operation at 1MW was achieved (All coolant temperature was saturated).

1MW-level oscillations of 104 GHz for 5s and 137 GHz for 6s were obtained.

203GHz oscillation has been demonstrated.

Long pulse operation : 0.4 MW for 5s (The world’s first)

Achieved maximum power : 0.9 MW/0.3ms

Experimental results of long pulse operations for 170 GHz and multi--frequency oscillations

If higher order mode TE49,17 mode in same mode-group is selected for 236 GHz oscillation, the oscillation power increases up to 1.35 MW (Output power ~ 1.2 MW). Multi-frequency oscillation (178GHz/207GHz/265GHz) is expected.

Compact loads for viewing ports

Dummy load for relief window

DC-break coolant (Fluorinert)

DC-breakAbsorber(Water)

MirrorsRadiatorCavity

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plin

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effi

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t [a

.u.]

Beam radius [mm]

TE19,7

TE37,13

TE31,11

TE25,9

1 1main subrad r

, main , sub

cos cos

m n m n

m mN

I. 1.0 MW steady state operation has been achieved for ITER, and over-1MW of 1.2MW with ~ 50 % have been demonstrated.II. Quad-frequency oscillations (0.9MW/5s/104GHz, 1MW/6s/137GHz, 1MW/300s/170GHz, 0.4MW/5s/203GHz) have been demonstrated. III. 236 GHz (TE43,15) for DEMO can be expected up to 0.9 MW output power even if the ITER gyrotron. Over-1 MW will be expected by exciting TE49,17 mode.

Summary

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Output power [MW]

(Pulse length > 2sec)

Maximum power : 1.23MW/47%

TE43,15 mode

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pow

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Oscillation efficiency [%

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Beam current [A]

fosci

~ 236.07 GHz

Vbeam

= 72 kV, = 1.2, Bc ~ 9.29 T

2 kW/cm2

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Osc

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pow

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MW

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Oscillation efficiency [%

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Beam current [A]

fosci

~ 235.98 GHz

Vbeam

= 72 kV, = 1.2, Bc ~ 9.28 T

2 kW/cm2

TE49,17 mode

Possibility of 236 GHz oscillation for demo-reactor generation

170GHz (Present design)

170GHz(Modified)

104GHz (Present design)

104GHz(Modified)

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170GHz(Modified)104GHz(Modified)170GHz(Present design)104GHz(Present design)

Tra

nsm

issi

on e

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%]

Radiator M1 M2 M3 M4 Window

97.4%

95.5%

98.5%98.1%

Target efficiencies is > 98 % at both frequencies.Improvement of 2 % is achieved at 104 GHz. The efficiency at 170 GHz is comparable.

Beam profile at radiator

(Beam voltage: 72kV and beam current : 40 A)

Cavity radius: 23.80 mm

Beam radius:10.31 mm

Window thickness : 2.14mm

Case 1 : ITER type gyrotron

Case 2 : Modified gyrotron