2019 Volume 14 Pages 1205038
High field side (HFS) injection of eXtra-ordinary X-mode for electron Bernstein wave (EBW) conversion was conducted in the QUEST tokamak. Radio frequency (RF; 8.2 GHz) power was delivered from the low field side (LFS) to the high field side HFS through waveguides, and from the HFS placed 20 cm above the mid-plane of the vacuum vessel. The aim was to compare the RF launches from the LFS and HFS. The plasma brightness, measured by a fast camera, as well as the Hα signal captured along the mid-plane, was noticeably higher in the HFS launch than in the LFS launch. The HFS injection achieved a plasma current of approximately 130 A, versus 35 A in the LFS injection. The electron density ne predicted from the position of the upper hybrid resonance agreed with the line-averaged ne measured by an interferometer, confirming the effective conversion and subsequent damping of the EBW mode. The RF leakage of the HFS injection was less than one-sixth that of the LFS injection. These results indicate that HFS delivers better RF coupling and conversion efficiency to EBW than LFS injection. Such efficient plasma heating via EBW will significantly enhance the plasma production.
