Design and RF test of a prototype traveling wave antenna for helicon current drive in KSTAR

Non-inductive current drive by fast wave at very high ion cyclotron harmonics, known as 'helicons' has the potential for high off-axis current drive efficiency compared with the other known non-inductive current drive techniques. However, non-inductive current drive by helicon wave has not been validated experimentally. To validate its anticipated performance experimentally, an antenna design is one of the most important issues. A Traveling wave antenna has particularly valuable features for launching the fast wave such as load resiliency, narrow n|| spectrum, and simple RF circuits without additional-external matching systems. Low power level helicon wave coupling experiments has been conducted successfully using a mock-up TWA in KSTAR. In the next step, in order to investigate a high power performance, a new prototype TWA based on the mock-up TWA has been designed, fabricated and measured for a medium power (100-300 kW) RF system. The prototype TWA having a Faraday shield was made of copper and consists of 10 current straps with 5 inch coaxial feeding lines as input and output ports. The detailed design parameters and electromagnetic characteristics of prototype TWA are discussed.