MHD Suppression with Modulated LHW on HT-7 Superconducting Tokamak* Support by National Natural Science Fund of China No J.S.Mao, J.R.Luo, B.Shen, J.Y Zhao, X.Gao, L.Q.Hu, Y.J.Shi, G.S.Xu, W.Z. Shen, S.D.Xu, J.F.Shan, P.K.Liu, Y.D.Fang, P. Phillips 1 Institute of plasma Physics, Chinese Academy of Sciences, P.O.box 1126,Hefei, Anhui, , China. 1 Fusion Research Center, C1510 Univ. of Texas at Austin. TX USA 4 th General Scientific Assembly of Asia Plasma & Fusion Association On New Development of Plasma Physics and Fusion Technology Hangzhou, China Oct 13 – 16, 2003

A crucial issue for the extension of advanced tokamak scenarios to long pulse operation is to avoid these MHD instabilities. In configurations with transport barriers the improved edge and core confinement leads to large pressure gradient and large edge bootstrap current density which often drive magnetohydrodynamic (MHD) terminating the discharge or reducing the discharge performance. The edge and the core transport barriers deteriorate or are completely lost. Tokamak major disruptions by the MHD perturbation in the Synergy of IBW and LHCD for High Performance Operation in the HT-7 Tokamak MOTIVATION HT-7

The various ways of suppression and control of the low order m / n tearing modes have been realized. Active control of MHD modes was achieved in ASDEX-U, JET and D-III by ECH The island heating with modulated ECH in DIII-D, with modulated LHW on JT-60U MHD suppression was achieved using resonant magnetic perturbation (RMP) or magnetic feedback A. Thyagaraja, R. D. Hazeltine, A. Y. Aydemir, Phys. Fluids B 4, 2733 (1992). Y. qingquan, et al Thansactions of Fusion Technology 27 (1995)459 MOTIVATION HT-7

ASIPP Various methods for suppression the tearing modes to prevent disruptions on HT-7 Tokamak 1.In the HT-7 IBW and LHCD synergetic discharges through moving the IBW resonant layer to maximize the plasma current density profile to avoid MHD activity. 2. Theory & technique of Dynamic Stabilization has been done on HT-7. MHD perturbation was suppressed effectively by  Oscillating plasma current on HT-7 Tokamak  Modulate plasma horizontal position  Modulate IBW  Modulate LHW  Modulate LHW & IBW on the Synergy IBW and LHW for High Performance Operation

MHD induced disruption with LHCD in Ip~ KA, Ne range 1.0~1.6 HT-7

Reproducible MHD activity was observed in discharges with LHCD in discharges with LHCD m=2 f= 7 kHz HH MHD LHW

HT-7 Island Width Calculation m=2 ~ cm White, R.B., et al., Phys. Fluids 20 (1977) 800 HT-7 ( with LHCD)

Ip =120KA Ne(0) = 1.0 (10 13 /cm 3 ) Bt ~1.8T (3800A) q(a)~ 4 HT q (r) r/a Deposited power density (Wcm -3 ) r / a A non-linear instability by LHW power deposited near the rational surface q=m/n, formated lager share. This results in the of rotating islands, located near the rational surface, ( for m/n=2/1 mode, the q=2 surface). LHW modulation would result in changes in current profile

HT-7 Different Forms of LHW Modulation The delivering time of LHCD pulse is less then 30  s. The amplitude, interval and the period of LHCD modulation pulse can be adjusted very conveniently.

HT-7 LHCD Efficiency

HT The continuous discharges with the same discharge conditions, the same wave power and the same launched wave spectrum of the LHCD Shot No Ip=100KA Ne=1.1X cm-3 Bt ~1.8T LHW=400KW (  = ms on, 10ms off )

time (ms) Shot No HT-7 time (ms) Shot No & No time (ms) Shot No The continuous discharges with the same discharge conditions, the same wave power and the same launched wave spectru of the LHCD Ip =100KA Bt =1.8T Ne(0) = 1.1 (10 13 /cm 3 ) LHW (  = KW ) Impurity suppression and No disruption Impurity suppression and No disruption with MHD suppression by LHCD modulation

Shot No & No Shot No time (ms) HT-7 time (ms) Impurity suppression and No disruption Impurity suppression and No disruption with MHD suppression by LHCD modulation The continuous discharges with the same discharge conditions, the same wave power and the same launched wave spectru of the LHCD Ip =100KA Bt =1.8T Ne(0) = 1.1 (10 13 /cm 3 ) LHW (  = KW ) time (ms) Shot No.54701

HT-7 MHD suppression by LHCD modulation Ip =110KA, Bt =1.80T, ne(0) ~1.0x10 13 cm -3 ( 20ms on, 10ms off )

Shot Shot ( 20ms on, 20ms off ) Shot ( 20ms on, 10ms off ) HT-7 The modulation of the current profile must be large enough to move the resonance q=2 surface outside the island width on a time scale faster than the growth time of the instability. Ip=150KA Ne=1.5 Bt=1.9T( It=3991KA) LHW (  = KW ) IBW(30M 160KW)

>1cm The modulation of the current profile must be large enough to move the resonance q=2 surface outside the island width on a time scale faster than the growth time(~50ms) [1] of the instability. HT-7 In the experiments on HT-7 the change in the current profiles near the q=2 surface were always faster than the growth time of the MHD modes. Suppression was achieved only when the q=2 resonance location was outside the island region [1][2] [1] J.S.Mao et al., NUCLEAR FUSION, Vol.41, No.11 (2001) 1645 ) [2] Y. qingquan, et al Thansactions of Fusion Technology 27 (1995)459 MHD suppression was achieved using resonant magnetic perturbation (RMP)

No (  = ms on, 10ms off); No.54753(  = ms on, 10ms off) HT-7 Different effect of MHD suppressed on the different wave spectra

There is some different effect of MHD suppressed on the different wave spectra launched with LHCD modulation HT-7 Synergy of IBW and LHCD for High Performance Operation LHCD

JT-60U

Comments Suppressing MHD activity by LHW modulation has been demonstrated on HT-7 tokamak The LHW modulation would result in changes in current profile. The changes must be large enough to move the resonance q = 2 surface outside the island width on a time scale faster than the growth time of the instability. The suppression of MHD activity (m=2) was observed when the LHW modulation amplitude was greater than 350KW. The more fast is better. Active control of MHD modes will be done in the future HT-7