Study of elliptical polarization requirement of KSTAR 84-GHz ECH system

Abstract

Since the efficiency of the Electron Cyclotron (EC) wave-heating and the wave-induced current drive depends on the mode of the wave propagating in tokamak plasmas, selective coupling of the wave to a particular plasma wave mode is required depending on the experimental objectives. Selective coupling into the wave mode in plasmas is determined by the incident-wave polarization and its ellipticity at the plasma edge. The incident-wave polarization and ellipticity are also control parameters to obtain the desired mode purity in the plasma center in EC wave heating and current drive experiments. For the KSTAR 84 GHz ECH system, two polarizer miter bends will be used to control the wave polarization and its ellipticity. Any wave polarization and ellipticity can be produced by changing the mirror rotation angle of each polarizer miter bend. This paper shows calculated ellipticity maps and mode purity maps as functions of the mirror rotation angle. For the mode purity maps, the plasma density and the toroidal magnetic field in the plasma center are assumed to be 1 x 10(19) m(-3) and 3.5 Tesla, respectively.