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.