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Development and Contribution of RF Heating and Current Drive Systems to Long Pulse, High Performance Experiments in JT-60U
Shinichi Moriyama, Masami Seki, Masayuki Terakado, Mitsugu Shimono, Shunsuke Ide, Akihiko Isayama,Takahiro Suzuki, Tsuneyuki Fujii and JT-60 Team
Japan Atomic Energy Research Institute
Symposium on Fusion Technology 2004, Venice, Sep 21, 2004
Contents
1. Overview of the JT-60U EC system
2. Steady state advanced tokamak research in JT-60U
3. Techniques for long pulse gyrotron operation
4. Modification of the LH antenna
5. Summary
JT-60U EC Heating and Current Drive System
Vacuum pumping
Acceleration power supply (100kV, 0.3A)
High Voltage DC Power Supplies
(each 60kV, 65A)
Amp. / Gyrotron Room
JT-60U
Transmission lines(~60 m, = 31.75 mm)
Torus Hall
(cross section)
Plasma
Waveguide Load
110GHz Gyrotron
MOU
FrequencyPower at gyrotronPower into TorusPulse durationNumber of gyrotrons
Transmission mode length efficiencyInner diameter of W/GPressure in w/g
HE11
~ 60 m~ 75% (9 bends / line)31.75mm10-4 ~10-3 Pa
110GHz4MW3MW5sec4
Original specifications
Antenna-A Antenna-B
Purposes of Long Pulse Experiments in JT-60U• Steady state advanced tokamak research
1. Long sustainment of high boot-strap current fraction
2. Long sustainment of high- plasma
3. Enhancement of in quasi steady state by stabilization of NTM
• The maximum duration of the plasma: 15 65 sec with modifications in only control systems.
• EC
–Local current drive for NTM stabilization / Current profile control/
–Electron heating / Plasma start-up
• LH
–Effective current drive / Current profile control to extend pulse duration of reversed shear plasmas
65sec Discharge Achieved with EC and NBPlasma duration : 15 sec 65 sec
without increase in energy resource of poloidal power supply : 1.3GJSaving volt-sec consumption by heating systems
Two EC Units assisted plasma start-up
One EC unit (0.5MW for 6sec) and 12 NB units (9MW peak for 30sec) for CD and heating
BT flat-top4.0T 8s (rated)3.3T 30s2.7T 60s
IP
NB
EC
Stabilization of Neoclassical Tearing Mode by ECCD
NBI
Feedback control on ECCD location•Beam angle control by steerable mirror antenna•Multi-channel ECE diagnostic
Instability Amplitude
ECCD
Demonstrated in JT-60U in FY2002
Gyrotron and Beam Current
Inter Lock for over current
0 1 2 3 4 5 6Time (sec)
0
60
80
40
20Bea
m C
urre
nt (
A)
Output power
1. Increase in beam current by parasitic oscillation limited the pulse duration < ~3sec.
RF output
4T
0.25 m
Parasitic RF
Anode
Diamond window
0.88
m
Electron beam
Superconductingmagnets
Resonator 40
Cathode
Body
Electron gun
Electronorbit
90GHz was detected around electron gun (~10% of Output Power)
radi
us (
mm
)
B (
T)
0
10
20
30
0Distance from cavity(mm)
50 100 150 200 250 300 350
B0
4
23
1Shape of Beam Tunnel
Electron beam orbit
Estimated Location of the Parasitic Oscillation
Collector
Gyrotron and Beam Current
Inter Lock for over current
Beam Current with RF absorber
Without RF absorber
0 1 2 3 4 5 6Time (sec)
0
60
80
40
20Bea
m C
urre
nt (
A)
Output power
1. Increase in beam current by parasitic oscillation limited the pulse duration < ~3sec.
2. SiC absorber had resolved the problem (4 sec at 1.2 MW )3. Decrease in beam current became a new problem for longer pulse
RF output
4T
0.25 m
Anode
0.88m
Diamond window
0.88
m
Electron beam
Superconductingmagnets
Resonator 40
SiC absorber
Cathode
Body
Electron gun
Electronorbit
•The pulse was terminated at 10.5 sec
Limitation of the pulse duration due to decay in beam current
0
10
20
30
40
-5 0 5 10 15 20
RFout (AU)
TIME(sec)
Normal
RF signalfrom directional coupler at MOU out
28
30
32
34
36
38
I C (A)
Normal
Collector (beam) current
•The oscillation condition was changed by the beam current decay
•Cathode cooling by electron emission
Problem in long pulse trial even at Pgyrotron~400kW
Power Supply and Anode Control Circuit
H
A
C
B
Gyrotron
K
AC
18kV/60kV
65AAcceleration P/S
Optical Signal
100kV/100mA
IGBT
Switch
100kV/100A
Body P/S
DC
4.45MVA
Timing
Generator Controller
JT-60U Control System
Local Control (sequencer)
Controller
Functional Generator
Heater
P/S
Anode Voltage Controller
•Fast IGBT switches•A unique voltage divider in the acceleration power circuit to apply and control anode voltage
Dummy Load System for Long Pulse Gyrotron Tests
Tank Load
Waveguide Load
Micro Wave from gyrotron1.88m
Sliding support for thermal expansion of waveguide load
Vacuum Pumping
Vacuum Pumping
1MW-CW-waveguide dummy load (GA)Special corrugation in 31.75mm WGHE11 EH11 surface wave (80% of incident power absorbed)4 litters/sec water cooling at ~500 kPa pressure drop
Keys of operationReleasing thermal expansion of the WG loadEffective vacuum pumping
28
30
32
34
36
38
I C (A)
Normal
Controlled
Collector (beam) current
0
10
20
30
40
-5 0 5 10 15 20
RFout (AU)
TIME(sec)
Normal
Controlled
RF signalfrom directional coupler at MOU out
0
5
10
I H (A)
Heater currentNormal
Controlled
The smaller decrement in the beam current
Demerit:•Large thermal capacity of heater-cathode system makes the time response slow•Temperature tends to be high in the next shot
Oscillation has been extended to 16 sec by Cathode Control
Heater current step up
Oscillation has been extended to 16 sec
(The target of 16sec was determined by temperature of Al2O3 DC break )
34
35
36
37Anode-Cathode voltage
V ak(kV)
Controlled : Vak=400V
Normal
0
10
20
30
40
-5 0 5 10 15 20
RFout (a.u.)
Normal
RF signalfrom directional coupler at MOU out
Controlled
Time (sec)
28
30
32
34
36
38
ControlledI C(A)
Normal
Collector (beam) current
•Anode voltage step uppossible only in triode type gyrotron
was not changed significantly
Oscillation has been extended to 16 sec by Anode Voltage Control
has been compensated the change in oscillation condition
•It is presumed that…
Modification of electron pitch angle at the electron gun
Oscillation has been extended to 16 sec = v / v// = v / v//
= v / v//
Optimization of Anode Voltage Control
5
10
15
20
0 200 400 600 800 1000 1200
Pulse duration t[sec]
Incriment of anode voltage Va[V]
w/o controlOverheat of mode converter(stopped at 100 C)
Pulse completed
Anode voltage step up by more than +600V
Significant temperature rise in the mode converter was observed
In these abnormal shots, the pulse was stopped manually watching at the mode converter’s temperature.
Through the trials, the optimum anode voltage change has been found to be +400V to achieve the pulse more than 15 sec
EC Power Injected to JT-60U• A prospect of 0.6 MW injection (0.8 MW at gyrotron) for
30 sec has been attained using 2 sets of 2units in series.• In high power mode, 3 MW for 5 sec is the tentative
target.
– Improvements has been done in cooling of the transmission system and in control system to prevent electrical noise.
0 1 2 3 4 5 60
0.5
1.5
1
2
2.5
3
3.5
Inje
cted
Pow
er (
MW
)
'00(3units)
'99
'99 (1unit)
'01
'01
'01
'01
Pulse Length (sec)
'01
(1unit)
(2units)
(3units)
(4units)(4units)
'02
'02
(1unit)
'02
7 11 12 13 14 15 168 9 10 17 18
(1unit)
Only this point indicatesthe gyrotron output power
'04 (1unit) '04
All the points indicate Injected power to JT-60U (= gyrotron output x 0.75)
Target in high power operation (4units)
Target in long pulse operation (4units) also...
0.6MW,30sec (2series of 2units) 0.3MW,60sec (1series of 4units)
(4units)‘04
W=18MJ
#1 #3#2 #4
T=0s 15s 30s
LH Antenna
CFC CFC
Graphite Graphite
Graphite
Original launcher mouth as it is for lower
half
726mm
Newly connected thin (~25mm) carbon grills
Please visit Poster 364 by M.Seki et al.
181.5mm
•The original antenna mouth had been partially deformed by heat load from the plasma and the RF breakdown for 10 years' operation.
•Graphite and CFC grills •high heat-resistant •quite less degrading plasma performance than stainless steel
•Improvement is expected in•power handling capability• durability against heat loads • Conditioning is under going
1.6 MW and ~10 MJ @ 2 GHz have been achieved by date
Summary1. A technique of anode voltage or heater control during a shot to
keep the oscillation condition against the beam current decay has been established.
2. In long pulse mode, 0.4MW (at gyrotron) 16 sec was attained.
3. A prospect of 0.6 MW injection (0.8 MW at gyrotron) for 30 sec has been attained using 2 sets of 2units in series.
4. In high power mode, 10 MJ (2.8MW, 3.6sec) has been achieved so far and further trial toward 3 MW for 5 sec is in progress.
Further contributions of the EC and LH system to long pulse high Further contributions of the EC and LH system to long pulse high performance plasma are expected in this experimental campaign performance plasma are expected in this experimental campaign of JT-60U.of JT-60U.