A feasibility study on a load resilient antenna for the KSTAR ICRF heating system

An effective rf power coupling for ELMy plasmas is one of the key issues for the ICRF heating. The conjugate T matching, which was adopted by the ITER design, is known to be an effective solution for this problem. The KSTAR ICRF antenna consists of 4 current straps with the transmission line configurations of resonant loops. The conjugate T matching concept is applied to each strap by conjugating the impedance of the upper and the lower parts of the resonant loops at the T point and the electrical lengths of the upper and the lower parts are adjusted by using the two phase shifters. In this work, the feasibility of a conjugate T matching is studied for the KSTAR ICRF antenna. With a mutual coupling of 20% between the upper and the lower current straps, the KSTAR antenna is investigated for its load resilient characteristics against a variation of the plasma loading resistance. In addition, the effects of a phase difference of the antenna current between the upper and the lower straps on a rf power coupling to plasmas are investigated by using a full wave simulation code.