Study of High Power ICRF Antenna Design in LHD

In large helical device (LHD), antenna loadings are different for minority ion cyclotron heating (MICH with 38.47 MHz) and mode-converted ion Bernstein wave heating (MC-IBW with 28.4 MHz), and it is necessary to improve antenna loading with low heating efficiency to avoid arching on transmission line. To design a new ion cyclotron range of frequencies (ICRF) antenna in LHD, calculation for a simple antenna model is conducted using three-dimensional electrical magnetic code (high frequency structure simulator, HFSS) for an water loading as an imaginary plasma with low heating efficiency. At resonant frequencies, antenna loading is sensitive to strap width, and resonant frequencies are strongly related to strap height. There is no differences of RF current profile on the strap surface between resonant frequency and non-resonant frequency. The strap should be perpendicularly placed against the magnetic field line, since Faraday-shield angle will lead to a decrease in the effective antenna height.