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Symposium on Fusion Technology 2004, Venice, Sep 21, 2004
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
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
Original specifications
Frequency
Power at gyrotron
Power into Torus
Pulse duration
Number of gyrotrons
Transmission mode
length
efficiency
Inner diameter of W/G
Pressure in w/g
110GHz
4MW
3MW
5sec
4
MOU
Antenna-A
HE11
~ 60 m
~ 75% (9 bends / line)
31.75mm
10-4 ~10-3 Pa
110GHz Gyrotron High Voltage DC
Power Supplies
(each 60kV, 65A)
Antenna-B
JT-60U
(cross section)
Plasma
Vacuum
pumping
Transmission lines
(~60 m, f = 31.75 mm)
Torus Hall
Waveguide Load
Acceleration power
supply (100kV, 0.3A)
Amp. / Gyrotron Room
Purposes of Long Pulse Experiments in JT-60U
•
Steady state advanced tokamak research
1.
2.
3.
•
Long sustainment of high boot-strap current fraction
Long sustainment of high- b plasma
Enhancement of b 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 NB

Plasma duration : 15 sec
65 sec
without increase in energy resource of poloidal power supply : 1.3GJ

Saving volt-sec consumption by heating systems
IP
NB
EC
BT
flat-top
4.0T
8s (rated)
3.3T 30s
2.7T 60s
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
Stabilization of Neoclassical Tearing Mode by ECCD
Demonstrated in JT-60U in FY2002
Feedback control on ECCD location
•Beam angle control by steerable mirror antenna
•Multi-channel ECE diagnostic
NBI
ECCD
b
Instability
Amplitude
Gyrotron and Beam Current
1. Increase in beam current by parasitic oscillation limited the pulse
duration < ~3sec.
90GHz was detected around electron gun (~10% of Output Power)
Electron beam
RF output
30
20
10
00
50
Body
Beam Current (A)
0.88m
4T
Parasitic RF
150
200
250
Distance from cavity(mm)
300
80
Resonator 40f
Superconducting
magnets
100
4
3
2
1
0
350
Inter Lock for over current
60
40
Output power
20
Electron gun
Anode
Cathode
Electron
orbit
0.25 m
0
0
1
2
3
4
5
Time (sec)
6
B (T)
Diamond window
Collector
radius (mm)
Estimated Location of the Parasitic Oscillation
Gyrotron and Beam Current
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
Diamond window
Electron beam
RF output
80
4T
Superconducting
magnets
Body
0.88m
0.88m
SiC absorber
Beam Current (A)
Resonator 40f
Inter Lock for over current
Without RF Beam Current with
absorber
RF absorber
60
40
Output power
20
Electron gun
Anode
Cathode
Electron
orbit
0.25 m
0
0
1
2
3
4
5
Time (sec)
6
Limitation of the pulse duration
due to decay in beam current
Problem in long pulse trial even at Pgyrotron~400kW
38
IC (A)
•Cathode cooling by electron
emission
Collector (beam) current
36
34
32
Normal
30
•The oscillation condition was
changed by the beam current decay
RF out (AU)
28
40
RF signal
30
from directional coupler at MOU out
20
10
0
•The pulse was terminated at
10.5 sec
Normal
-5
0
5
TIME(sec)
10
15
20
Power Supply and Anode Control Circuit
•Fast IGBT switches
•A unique voltage divider in the acceleration power
circuit to apply and control anode voltage
JT-60U Control System
Local Control (sequencer)
Timing
Generator
Functional Generator
Controller
Controller
Gyrotron
Heater
P/S
H
IGBT
K
Switch
100kV/100A
A
Body P/S
Optical
Signal
B
100kV/100mA
4.45MVA
AC
DC
18kV/60kV
C
Anode Voltage Controller
65A
Acceleration P/S
Dummy Load System for Long
Pulse Gyrotron Tests
Tank Load
1.88m
Micro Wave from gyrotron
Vacuum Pumping
Vacuum Pumping
Sliding support for thermal
expansion of waveguide load
Waveguide Load
1MW-CW-waveguide dummy load (GA)
Special corrugation in 31.75mm WG
HE11
EH11 surface wave (80% of incident power absorbed)
4 litters/sec water cooling at ~500 kPa pressure drop
Keys of operation
Releasing thermal expansion of the WG load
Effective vacuum pumping

Oscillation has been extended to 16 sec by
Cathode Control
IH (A)
10
Heater current step up
Controlled
5
Normal
Heater current
0
38
Collector (beam) current
IC (A)
36
34
Controlled
32
Normal
30
RFout (AU)
RF signal
from directional coupler at MOU out
Controlled
20
Normal
10
0
Oscillation has been
extended to 16 sec
(The target of 16sec was determined
by temperature of Al2O3 DC break )
28
40
30
The smaller decrement in the
beam current
-5
0
5
10
TIME(sec)
15
Demerit:
•Large thermal capacity of heatercathode system makes the time
response slow
•Temperature tends to be high in the
20
next shot
Oscillation has been extended to 16 sec by
Anode Voltage Control
Vak(kV)
37
Anode-Cathode voltage
36
Controlled : V ak=400V
35
•Anode voltage step up
possible only in triode type gyrotron
Normal
34
38
Collector (beam) current
was not changed significantly
36
IC(A)
a = v^ / v// 34
32
Controlled
Normal
30
RF out (a.u.)
28
40
30
•It is presumed that…
Modification of electron pitch
angle at the electron gun
a = v^ / v//
RF signal
from directional coupler at MOU out
Controlled
20
Normal
10
0
-5
Oscillation has been
extended to 16 sec
0
5
10
Time (sec)
has been compensated the
change in oscillation condition
15
20
Optimization of Anode Voltage Control
Anode voltage step up by
more than +600V
Pulse duration t[sec]
20
Pulse completed
Significant temperature rise
in the mode converter was
observed
15
10
5
w/o control
Overheat of mode converter
(stopped at 100 C)
0
200
400
600
800 1000 1200
Incriment of anode voltage Va[V]
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
•
#1
A prospect of 0.6 MW injection (0.8 MW at gyrotron) for
#2
30 sec has been attained using 2 sets of 2units in series. T=0s
In high power mode, 3 MW for 5 sec is the tentative target.
•
–
15s
Improvements has been done in cooling of the transmission
system and in control system to prevent electrical noise.
All the points indicate Injected power to JT-60U (= gyrotron output x 0.75)
3.5
Injected Power (MW)
#3
#4
'01
3
2.5
Target in high power operation (4units)
'01 '02
(4units)
'02
2
'01(4units)
‘04(4units)
'01 (3units)
'00
(3units)
1.5
'01
(2units)
W=18MJ
'02
1
0.5
0
Target in long pulse operation (4units)
also...
0.6MW,30sec (2series of 2units)
0.3MW,60sec (1series of 4units)
'99
(1unit)
(1unit)
'04 (1unit)
'99 (1unit)
0
1
2
3
4
5
6
Only this point indicates
the gyrotron output power
'04
(1unit)
7 8 9 10 11 12 13 14 15 16 17 18
Pulse Length (sec)
30s
LH Antenna
726mm
181.5mm
CFC
Graphite
Graphite
CFC
Graphite
Original launcher
mouth as it is for lower
half
• Conditioning is under going
•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
Newly
•high heat-resistant
connected
thin (~25mm)
•quite less degrading plasma
carbon grills
performance than stainless
steel
•Improvement is expected in
•power handling capability
• durability against heat loads
1.6 MW and ~10 MJ @ 2 GHz have been achieved by date
Please visit Poster 364 by M.Seki et al.
Summary
1. 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
performance plasma are expected in this experimental campaign of
JT-60U.