Traveling-wave antenna for the current drive using the fast wave in the lower hybrid-frequency range in the Versatile Experiment Spherical Torus (VEST)

Abstract An antenna using the fast wave in the lower hybrid-resonance frequency range is proposed for the significant attainment of the heating and current-drive efficiencies. For the operational stability regarding the change of the plasma load, the proposed antenna is designed as the combline-structure traveling-wave antenna. It consists of two tapered coaxial cables, two exciting straps of the folded-monopole structure, 12 radiating straps, 11 field isolators, and the Faraday shield. Regarding the vacuum load, the simulated and measured results show the wide impedance bandwidth (45 MHz, VSWR || ) is from 3 − 4.5 in the operational frequency band of 475–510 MHz.