Current profile control and optimization under dominant electron heating in HL-2A

The establishment of the current profile as in the hybrid scenario is studied under the condition of dominant electron heating in HL-2A. The scenarios with injecting lower hybrid (LH) and electron cyclotron (EC) waves are under numerical study. Carefully adjusting the position of non-inductive current driven by two groups of gyrotron, an optimized q-profile was obtained with qa = 3.78 and a weak shear region extending to ρ ∼ 0.45 (where ρ is the square-root of toroidal flux normalized to its value at the plasma boundary) in low-density discharges of . When 0.5 MW LH power in the current drive mode and 0.95 MW EC power mainly for plasma heating are used to control the current profile, a hybrid discharge scenario with a weak magnetic shear region extended to ρ = 0.6 and qa = 3.21 is established by controlling the EC absorption position. The mechanism of the LH wave absorption in the HL-2A plasma causes interplay of the distribution of the LH driven current with the modification of the plasma configuration, which constitutes non-linearity in the LH wave deposition. Due to the non-linearity the LH wave deposition position changes spontaneously or oscillates. The oscillatory behaviour caused by the non-linear effect of the LH wave deposition is analysed.