ECCD Experiments in Heliotron J, TJ-II, CHS, and LHD

Abstract

Electron cyclotron current drive (ECCD) experiments were conducted in the stellarator/heliotron (S/H) devices, such as Heliotron J, TJ-II, CHS, and LHD. Experimental results show that ECCD can be controlled by the power injection angle, absorption position and magnetic field structure. The current drive efficiencies are similar, γ = n_eI_ECR/P_EC = 8 - 16×10¹⁶ A/Wm² , ζ = 32.7n_eI_ECR/P_WT_e = 0.03-0.05, when the magnetic field ripple ratio is 0.93 < B_min/B_max < 1.0. The reversal of driven current direction is observed depending on the magnetic field ripple structure, indicating that the amplitude and direction of EC current is determined by the balance between the Fisch-Boozer effect and the Ohkawa effect, and that the Ohkawa effect is stronger in S/H devices compared with tokamaks. Control of net toroidal current by using ECCD is demonstrated; a net zero current state is attained by cancelling the bootstrap current.