Antenna and transmission system for high power electron cyclotron heating in a compact helical system

An electron cyclotron heating (ECH) system for the compact helical system using two types of high power gyrotron as a power source is designed. In order to utilize fully the advantage of the ECH, the antenna system is designed so as to inject the microwave power as an elliptic gaussian beam, which allows well-defined high power local heating. This antenna and associated transmission system from gyrotron are designed with the quasi-optical concept. This design concept and the results of the cold test for the transmission and antenna system are described. The resultant beam parameter of the cold test for the antenna system shows fairly good agreement with the designed value, which indicates the validity of this design concept. The power transmission efficiency of about 90% was estimated from the measured power at both ends.