Estimation of the current driven by residual loop voltage in LHCD plasma on EAST Tokamak

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The lower hybrid wave current drive (LHCD) is one of the efficient methods of driving the non-inductive current required for Tokamak operating in steady-state. Residual loop voltage exists in Tokamak when the non-inductive current is not fully driven. Residual loop voltage also accelerates the fast electrons generated by the lower hybrid wave (LHW), which can drive extra current and combine with the current driven by the LHW. It is generally difficult to separate these two different components of driven current in the experiment. In this paper, the currents driven by LHCD and residual loop voltage are separated directly by solving the Fokker–Plank equation numerically. The fraction of the current driven by residual loop voltage compared to the current driven by LHW is evaluated on the experimental advanced superconducting tokamak (EAST). The current driven by residual loop voltage is several percent of the currents driven by the LHCD when the residual loop voltage is small, but it increases with the residual loop voltage up to 25% when the residual loop voltage is about 2 V. The hot electrical conductivity is deduced from the net current driven by the residual loop voltage. Its distribution profile is related to the fast electron distribution driven by LHW.