1. 1 Instabilities in the Long Pulse Discharges on the HT-7 X.Gao and HT-7 Team Institute of Plasma Physics, Chinese Academy of Sciences, P.O.Box 1126, Hefei, Anhui 230031, P.R.China (e-mail: xgao@ipp.ac.cn) 4th General Scientific Assembly of Asia Plasma & Fusion Association On New Development of Plasma Physics and Fusion Technology, Hangzhou, China, Oct. 13-16, 2003 HT-7 ASIPP

2. 2 Abstract In the HT-7 superconducting tokamak, long-pulse discharge can be generated by synergy of high power LHCD (300-600 kW, 2.45 GHz) and high power IBW (200-350kW, 27 MHz) heating; MHD behaviors and thermal instabilities which limited the high performance operation was studied in detail; For lower performance (Ip = 60 kA, Te(0) = 0.5-1 keV, = 0.5-1xE19 m-3) operation, more than 60 s of long pulse plasma was obtained by the LHCD (< 200 kW) in the HT-7 tokamak.

3. 3 HT-7 Superconducting Tokamak R = 1.22m, a = 0.27m Ip = 100~250 kA (250) B T = 1~2.5T(2.5) n e = 1~8x10 13 cm -3 (6.5) Te = 1~5 KeV (4) Ti = 0.2~1.5K eV (1.5) ICRF: f = 15~30MHz, P=0.3MW(0.35) f = 30~110MHz, P = 1.5MW LHCD: f = 2.45GHz, P = 1.2MW(0.8) Fuelling: Pellet injector Supersonic beam injection Main Goal: Advanced Steady state operation and related physics

4. 4 Candidates for long pulse operation in the HT-7 (1) Low hybrid current drive (LHCD) LHW: 100 ~ 800 kW, the current drive efficiency: 0.5-0.8E19 A/m2W V loop = 0, = 0.8E19/m3, Ip > 100 kA @ 140 kW, t > 10 s Thermal instabilities: impurity, outgassing, and uncontrolled density (2) Full non-inductive current drive by synergy of LHW and IBW heating (LHCD + bootstrap current) ITB-like T i, T e, n e profiles, high beta plasma  N = 2 ~ 3, I BS /Ip up to 38% Thermal instabilities MHD instabilities: sawtooth, mode locking, collapse and disruption Reference: [1]X.Gao et al., “Study of LHW and IBW Synergy Experiment on the HT-7 Superconducting Tokamak”, 18 th IAEA Fusion Energy Conference (Sorrento, Italy, 4-10 October 2000), IAEA-CN-77/EXP4/12. [2]B.Wan et al., “Investigation of the Synergy of IBW and LHCD for Integrated High Performance in the HT-7 Tokamak”, 19 th IAEA Fusion Energy Conference (Lyon, France, 14-19 October 2002), IAEA- CN-94/EX/P3-20.

5. 5 Limitation of long pulse discharges during LHCD Heat exhaust and particle control High performance PFCs Plasma Control LHW system Edge physics impurityoutgassing uncontrolled Ne Thermal instabilities MoI Limiter

6. 6 Ip = 104kA, N e0 = 1.2x10 19 m -3, P LHCD =140kW, B T =2.0T

7. 7 Long pulse operation (>1 min) by LHCD

8. 8 Progress of Long Pulse Operation in the HT-7 Superconducting Tokamak

9. 9 Comparison between LHCD and IBW+LHW Ip = 150 kA, Bt = 2T, N || = 2.35 LHW: near on-axis current drive in target plasma IBW: 30MHz, on-axis heating Broadened HXR profile Increased driven efficiency Improved particle and energy confinement Peak position of HXR ~ first maximum of IBW n ||

10. 10 ITB by synergy of IBW and LHCD Ip = 200 kA, Bt = 2T, N || = 2.35 LHW: near on-axis current drive in target plasma IBW: 27MHz, off-axis heating ~ 0.5a Similar profiles as in IBW heating Strong gradient in pressure ~0.5a Improved particle and energy confinement ITB

11. 11 H89*  N > 3, Te(0) > 3keV by high power

12. 12 80% non-inductive current by IBW+LHW Ip = 120 kA, Bt = 1.8 T, V loop = 0.25 V, Te(0) = 2.2keV, ne(0) = 2xE19 /m3 H89*  N > 2 for ~ 200  E and f LHCD +f BS = 80% f BS = 38% f LHCD = 42%

13. 13 Collapse during IBW + LHCD Ip = 150 kA Bt = 1.8 T =1.5E19/m3 Collapse LHW: 200 kW IBW: 200 kW (30MHz)

14. 14 Sawtooth instability during IBW + LHCD Ip = 200 kA Bt = 1.8 T = 1.8-3.2 xE19 /m3 LHW: 540 kW IBW: 230 kW (27MHz) Sawtooth oscillations Proposal of sawtooth suppression by ECRH: D.Zhou at this meeting

15. 15 m=2 mode locking during IBW + LHCD Ip = 120 kA Bt = 1.7 T =1.2E19/m3 Mode locking LHW: 465 kW IBW: 220 kW (27 MHz) MHD suppression by modulated LHW: J.S.Mao at this meeting

16. 16 LHCD IBW MHD behaviors in high beta plasmas (IBW+LHW) Ip=125kA, ne=1.4x10 13 cm-3, Bt=1.75T, LHW=290KW, IBW=200KW (27MHz): Larger sawtooth  m=2 mode  disruption Collapse

17. 17 Full non-inductive CD by IBW + LHCD Ip = 120 kA, Bt = 1.6 T, V loop ~ 0 V ne(0)=1.5xE19 /m3, Te(0)=2.3 keV f LHCD = 73%, f BS = 27% LHW: 500 kW IBW: 200 kW(27MHz), near-axis heating @ high field r/a = -0.2 Sawtooth free Improved confinement

18. 18 Conclusion Progress of long pulse operation is summarized for HT-7 tokamak. Candidates for advanced steady state operation is discussed; In the HT-7 superconducting tokamak, long-pulse discharge can be generated by synergy of high power LHCD (300-600 kW, 2.45 GHz) and high power IBW (200- 350kW, 27 MHz) heating; MHD behaviors and thermal instabilities which limited the high performance operation was studied; For lower performance (Ip = 60 kA, Te(0) = 0.5-1 keV, = 0.5-1xE19 m-3) operation, more than 60 s of long pulse plasma was obtained by the LHCD (< 200 kW) in the HT-7 tokamak.

19. 19 Acknowledgement This work has been supported by the National Nature Science Foundation of China, contract number: 10005010. This work was also supported partly by JSPS-CAS Core-University Program on Plasma and Nuclear Fusion in 2003.