Lower Hybrid Wave Current Drive Efficiency on the HT-7 Tokamak

Lower hybrid (LH) wave current drive efficiency on our HT-7 tokamak has been investigated based on the hot electrical conductivity theory. The interaction of the residual toroidal electric field with fast electrons has been included in the determination of current drive efficiency. The LH wave power scan was performed in the plasma parameter ranges of I_p=50-156kA, ň_e=0.5×10^1.6-1.6× 10¹⁹m^-3, P_LH=50-350kW. The current drive efficiency is derived to be about 0.1× 10¹⁹-0.4×10¹⁹Am^-2W^-1 on the HT-7 tokamak, which depends on the electron density and the LH wave phase velocity. At the electron density of about 1.5×10¹⁹m^-3, with the LH wave parallel refraction index peaked at 1.8, the highest current drive efficiency was obtained. A more generally normalized method is introduced to analyse the experimental data, which combines all the data in one curve. The normalized parameters are independent of the plasma parameters.