Current Drive Experiments with Oscillating Toroidal Flux in HT-7 Superconducting Tokamak J.S.Mao, P. Phillips 1, J.R.Luo, J.Y.Zhao, Q.L.Wu, Z.W.Wu, J.G.Li, and HT-7 team Institute of plasma Physics, Academia Sinica, Hefei, Anhui, , P.R.China 1. Fusion Research Center, RLM UT at Austin. TX USA * Support by National Natural Science Fund of China HT-7 ASIPP

HT-7 ASIPP MOTIVATION  A crucial issue for the extension of advanced tokamak scenarios to long pulse operation is to avoid these MHD instabilities  The control of the low order m / n tearing modes has attracted much research  Various methods proposed to suppress the tearing modes to prevent disruptions  MHD suppression was achieved using resonant magnetic perturbation (RMP) or magnetic feedback  MHD suppressing has been research with new methods  Oscillating plasma current on HT-7 Tokamak  Modulate plasma horizontal position  Modulate LHCD  Modulate IBW

HT-7 ASIPP Experimental Set-up * The feedback control system for the HT-7 tokamak is a multi-variable feedback controller due to the strong coupling between the ohmic heating coil and vertical field coil. Input parameters: plasma current; vertical coil's current; center of the last magnetic surface as measured by the four single flux loops. * The output parameters are the ohmic heating current and the vertical coil's current. Response time of the feedback system is limited by double copper shell to greater than 200ms.

HT-7 ASIPP Toroidal flux was modulated by programming the ohmic heating field or by vertical field two types of experiments have been performed  Involves modulating plasma current only, while the other experimental parameters are held constant  Modulating plasma horizontal position with the plasma current kept constant by a feedback system Experimental Set-up

HT-7 ASIPP t (ms) I p B r SX Ne(0) ECE KA a.u. a.u cm -3 a.u.. (e) (d) (c) (b) (a) Modulating plasma current only, while the other experimental parameters are held constant Ip=114KA, dIp/Ip=30%, f=40Hz Negative Pulses -dIp/dt=5.43MA/s, + dIp/dt =2.4MA/s, Total radiation (Bol.) modulated and decrease Te(0) increased MHD suppressed

HT-7 ASIPP Shot No Time (ms) Bol Ne(0) SX(0) I p KA a.u.  cm -3 HT-7 Tokamak KA V a.u cm a.u Time (ms) Shot N IpVla1IpVla1 III

R=65cm, a=18.7cm, B t =1.0T, I p =60kA. Ip=60-70KA, dIp/Ip=14-20%, +dIp/dt=120MA/s, - dIp/dt=5.3MA/s, f<200Hz HT-7 ASIPP HT-6M Tokamak

HT-7 ASIPP ( II ) (1) Typical Discharge of the HT-7 Tokamak with Modulation Plasma Current

HT-7 ASIPP Modulating plasma horizontal position with the plasma current kept constant by feedback time (S) Ip Vp Iv  H SX Ne 120 KA V V 0 a.u a.u

HT-7 ASIPP Plasma Minor Radius Modulated  a ~ 3 cm– 5 cm The time and spatial distribution of bolometer signal with the plasma horizontal displacement modulated Raw Data of Soft X-Ray array

HT-7 ASIPP KA V a.u cm a.u Time (ms) Shot N IpVla1IpVla1 III Ne (r) Te(r) during TFCM

HT-7 ASIPP KA V a.u cm a.u Time (ms) Shot N IpVla1IpVla1 III Profile Changes during TFMC r (cm ) Ne ( cm -3 )

HT-7 ASIPP time (ms) LPI HX  H Ip V KA Suppression of MHD the edge potential fluctuation HX emission Long Pules Discharge without wall condition

HT-7 ASIPP radiation （ 10eV-10keV) MHD instability was reduced Modulated IBW heating AC IBW

HT-7 ASIPP LHCD Time (ms) KAKA V a.u. V l I p MHD modulated with AC curret & AC LHCD AC LHCD

Conclusion HT-7 ASIPP The plasma equilibrium current modulated by a frequency current has been successful used in suppressing MHD perturbations effectively on the HT-7 superconducting tokamak and HT-6M tokamak to suppression MHDControl of the plasma pressure profile with local modulated IBW heating can be possible to suppression MHD Modulating and Suppression MHD by modulating LHCD The resonant magnetic surfaces perturbations with different ways, It is difficult for the instability of the tearing modes to develop in some fixed locations.The resonant magnetic surfaces perturbations with different ways, It is difficult for the instability of the tearing modes to develop in some fixed locations.