Comparison of high-field-side and low-field-side launch ECCD in the W7-AS stellarator

The electron cyclotron current drive (ECCD) with extraordinary mode at the second cyclotron harmonic launched from the high-field-side (HFS) is investigated in W7-AS stellarator. Trapped particle effects and quasi-linear effects are taken into account in linear ray-tracing and quasi-linear bounce-averaged Fokker–Planck computations of the driven current. The results for both low-field-side (LFS) and HFS injection in W7-AS are compared with the experimental results. A slightly lower current drive efficiency is obtained, both theoretically and experimentally, in the case of HFS injection, confirming the LFS launch as the preferred mode of operation for ECCD.