1. 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

2. 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

3. 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 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 HE 11 ~ 60 m ~ 75% (9 bends / line) 31.75mm 10 -4 ~10 -3 Pa 110GHz 4MW 3MW 5sec 4 Original specifications Antenna-AAntenna-B

4. 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

5. 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 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 B T flat-top 4.0T 8s (rated) 3.3T 30s 2.7T 60s IPIP NB EC

6. Stabilization of N eoclassical T earing M ode 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

7. Gyrotron and Beam Current Inter Lock for over current 0123456 Time (sec) 0 60 80 40 20 Beam Current (A) Output power 1.Increase in beam current by parasitic oscillation limited the pulse duration < ~3sec. RF output 4T4T 0.25 m Parasitic RF Anode Diamond window 0.88m Electron beam Superconducting magnets Resonator 40  Cathode Body Electron gun Electron orbit Collector

8. Gyrotron and Beam Current Inter Lock for over current Beam Current with RF absorber Without RF absorber 0123456 Time (sec) 0 60 80 40 20 Beam Current (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 4T4T 0.25 m Anode 0.88m Diamond window 0.88m Electron beam Superconducting magnets Resonator 40  SiC absorber Cathode Body Electron gun Electron orbit

9. The pulse was terminated at 10.5 sec Limitation of the pulse duration due to decay in beam current The oscillation condition was changed by the beam current decay Cathode cooling by electron emission Problem in long pulse trial even at P gyrotron ~400kW

10. Power Supply and Anode Control Circuit H A C B Gyrotron K AC 18kV/60kV 65A Acceleration 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

11. Dummy Load System for Long Pulse Gyrotron Tests Tank Load Waveguide Load Micro Wave from gyrotron 1.88m Sliding support for thermal expansion of waveguide load Vacuum Pumping 1MW-CW-waveguide dummy load (GA) Special corrugation in 31.75mm WG HE 11 EH 11 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

12. 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 Al 2 O 3 DC break )

13. Anode voltage step up possible 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 //

14. Optimization of Anode Voltage Control w/o control Overheat 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

15. 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. #1 #3 #2 #4 T=0s 15s30s

16. LH Antenna CFC 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

17. 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.