Development of an arch antenna for LHCD in a spherical tokamak

A lower-hybrid frequency surface wave antenna called arch is designed and fabricated in this paper for the spherical tokamak named EXL-50. It is used to drive plasma current and heat plasma at 2.45 GHz. The arch antenna consists of 27 antenna elements. The left and right rectangular waveguides integrated with the antenna are used for microwave input and output, respectively. The refraction parallel index of this proposed antenna is $4.3$ , which is favorable for the lower hybrid current drive. The measurement results in the absence of plasma show that the reflection and transmission coefficients ( $S11$ and $S21$ ) are $ - 12.5\;{\text{dB}}$ and $ - 12.6\,{\text{dB}}$ , respectively. The antenna was installed and tested on EXL-50. Up to a $35{\text{ kA}}$ plasma current was achieved using the arch antenna with a microwave of $70{\text{ kW}}$ .