HT-7 Proposal of the investigation on the m=1 mode oscillations in LHCD Plasmas on HT-7 Exp2005 ASIPP Youwen Sun, Baonian Wan and the MHD Team Institute of Plasma Physics, Chinese Academy of Sciences P.O.Box 1126, Hefei,Anhui ,P.R.China

HT-7 2 Outline 1.The last experimental results 1). Introduction 2). Observation 3). Mode Analyses and conclusion 2. New experimental proposal

HT-7 3 Introduction A new oscillation with m/n=1/1, where m and n are the poloidal and toroidal mode numbers respectively, has been observed with Lower Hybrid Current Drive (LHCD) on the HT-7 tokamak. Soft X-ray array Typical parameters: R=1.22, a=0.27, n e ~ 1.5×10 19 m -3, T e ~ 1keV, I p ~150 kA, B T ~2T, LHCD: n || peak =2.3 The temporal evolution of the soft-X-ray emission intensity.

HT-7 4 Outline 1.The last experimental results 1). Introduction 2). Observation 3). Mode Analyses and conclusion 2. New experimental proposal

HT-7 5 Observation LHCD power scan The dependence of the sawtooth periods on the LHCD power The sawtooth behavior at the beginning of the LHCD. when the sawtooth period exceed a critical value, the m = 1 mode appears during the ramp phase of the sawtooth.

HT-7 6 Observation Mode amplitude The dependence of the maximum amplitudes of the m=1 mode normalized to the total intensity of the central soft-x- ray emission on the LHCD power The dependence of the maximum amplitudes of the m=1 mode on the edge safety factor q a.

HT-7 7 Observation Mode growth rate on q a

HT-7 8 Outline 1.The last experimental results 1). Introduction 2). Observation 3). Mode Analyses and conclusion 2. New experimental proposal

HT-7 9 Mode analyses and conclusion Mode analysis (1) Mode structure obtained from SVD analysis Contour plot of the soft X-ray perturbation signals

HT-7 10 Mode analyses and conclusion Mode analysis (2) The spatial profile of the soft-x-ray signals at different times

HT-7 11 Mode analyses and conclusion Mode analysis (3) The dependence of the calculated magnetic shear at the q=1 surface on q a. Current model: J ~ (1-x 2 ) α q =q a x 2 /[1-(1-x 2 ) α+1 ]

HT-7 12 Mode analyses and conclusion Conclusion One possible evolution of the m=1 mode and the local magnetic shear at the q=1 surface This mode may be destabilized by the current density gradient, the evolution of which is determined by the suprathermal electrons generated by the LHCD. This result has been submitted to Plasma Physics and Controlled Fusion (accepted).

HT-7 13 Outline 1.The last experimental results 1). Introduction 2). Observation 3). Mode Analyses and conclusion 2. New experimental proposal

HT-7 14 New experimental proposal 1.Some supplements for the experimental data. To investigate the behavior of the m=1 mode in the following condition: 1). High power (?). 2). High q a. 3). Long period sawtooth or sawtooth free.

HT-7 15 New experimental proposal 2. To investigate the m=1 mode behavior with different current profile, which can be obtained through changing the LH phase angle and plasma density. 3. Using the hard X-ray array detecting the fast electrons profile and its evolution to study the relation between the loss of the fast electrons and the m=1 mode behavior.

HT-7 16 Thank you!