Influence of Li conditioning on Lower Hybrid Current Drive efficiency in H-mode and L- mode plasmas on EAST.

The lower hybrid current drive efficiency on the EAST tokamak is estimated on a large database of low loop voltage discharges (V_L<120mV) covering the 2016 campaign starting with lithium-free plasma facing components and ending with strong cumulated deposition of lithium. The efficiency is found to vary in a wide range from 0.6 to 1.2×10¹⁹A.W^-1.m^-2. No deleterious effect of the density on the efficiency is found between 2.3 and 3.2×10¹⁹m^-3. The high efficiency occurs after strong lithium evaporation. The low effective charge Zeff and the higher temperature <Te> of these discharges, can account for the high efficiency according to the expected scaling with Zeff and <T_e>. Modelling with a ray-tracing code coupled to a Fokker-Planck solver supports this result, assuming that the fast electron transport is reduced in the zero loop voltage discharge with high efficiency. [ABSTRACT FROM AUTHOR]