Lower Hybrid Wave Coupling and Current Drive Experiments in HT-7 Tokamak Weici Shen Jiafang Shan Handong Xu Min Jiang HT-7 Team Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, , P.R.China ASIPP HT-7

Experimental set-up Lower hybrid wave coupling experiment LHCD improve confinement LHCD+IBW synergy experiment Long pulse discharge with LHCD HT-7 ASIPP Outline

1.2MW/2.45GHz LHCD System HT-7 ASIPP

Multijunction Grill Antenna HT-7 ASIPP  N //  N //

Simulation of the lower hybrid wave power deposition and drive current Ip=150kA, n e =1E10 13 cm -3, B T =1.8T, T e =1keV HT-7 ASIPP

Reflection coefficient and Loop voltage versus spectrum and plasma parameters HT-7 ASIPP The incident and reflected powers are determined from the performed by 12 bidirectional couplers. Lower power reflection coefficients and higher current drive efficiency are obtained when phase is between 0 o and 90 o. The mean reflection coefficient never exceeds 10%. B T =1.6~2 T I p =100~200kA n e =1~2.5×10 13 cm -3

HT-7 LHCD Typical Discharge Ip=220kA, ne=1.5E13, Bt=1.8T, P LH =320kW HT-7 ASIPP

LHCD Improve Confinement HT-7 ASIPP τp OH ≈ 10ms τp LHCD ≈ 45ms τ E OH ≈ 4.9ms τ E LHCD ≈13.5ms. Ip=150kA P LH =300kW B T =2T Ne 1.2~3 High performance phase

Electron Heating and Internal Transport barrier formed during LHCD P LH =320kW,  Te=500eV, r ITB =0.37a HT-7 ASIPP

Some diagnostic measurement results during LHCD Experiments HT-7 ASIPP hard X-ray intensity distribution Electron thermal diffusivity  e LHW modifies the edge E r Soft X-ray signals

The simulated result shows that off-axis LH power deposition makes a hollow current profile during the LHCD phase, which indicates that a negative magnetic shear,or at least, a low magnetic shear is formed. HT-7 ASIPP Simulation of the LH Power Deposition and Plasma Current, q Profile

LHCD+IBW Synergy Experiment HT-7 ASIPP In high LH power combined with IBW heating scenario, a good heating effect has been observed (Te ~ 4keV). At this time, a good stationary wave coupling is maintained with reflection coefficient less than 3 %.

LHCD+IBW Synergy Effect A efficient for heating the bulk ion and electron of the plasma is observed. A strong HXR emission is observed for combined LHW/IBW operation HT-7 ASIPP

64 second discharge with LHCD HT-7 ASIPP

Conclusion HT-7 ASIPP The new multijunction launcher, the reflect wave is very sensitive to the phase between adjacent waveguide units. A good stationary coupling is maintained when 2  N //  3.1. The mean reflection coefficient never exceeds 10%. The maximum LH wave power coupling to the plasma is above 600kW. The high performance plasma enhanced confinement has been observed with LHCD. The plasma configuration with electron ITB has been obtained in LHCD by optimizing plasma and wave parameters. The eITB is triggered at the beginning of the LH wave inputting and sustained all LHCD phase. The simulation results show that off-axis LH power deposition make a hollow current profile. The current density profile modify by using LHCD. A good heating and improve confinement effect has been achieved during LHCD+IBW synergy experiment. More than 1 minter long pulse plasma discharge has been achieved.

Acknowledgements: The experiments are supported by HT-7 Operation, Diagnostic Group, Data Acquisition, and LHCD Group. The authors would like thank for their cooperation and kindly help. HT-7 ASIPP References: [1] Y. Peysson and the Tore Supra team, Nuclear Fusion, 41, (2001). [2] S. Ide, et al., Proceedings of 16 th International Conference on Fusion Energy, Montreal, 1996, (International Atomic Energy Agency, Vienna, 1997) IAEA-CN-64/E-3. [3] S. Ide, O. Naito, T. Oikawa, T. Fujita, T. Kondoh, M. Seki, K. Ushigusa and JT-60 Team, Nuclear Fusion 40, 445 (2000). [4] G.L. Kuang et al., Nuclear Fusion, 39(11), 1769 (1999). [5] B.J. Ding et al., Phys. Plasmas, Vol. 9, No. 12, 4996 (2002). [6] W.C. Shen et al., Plasma Science & Technology Vol.5, No (2003).