Electron Bernstein wave heating in heliotron configurations

Abstract

Electron Bernstein wave heating is calculated for conventional heliotron configurations by using a ray tracing numerical code in which three-dimensional magnetic field structure is considered. The ordinary (O)-extraordinary (X)-electron Bernstein (B) and X-B conversions are treated. In the O-X-B heating, since the magnetic shear is strong and the poloidal field is comparable with the toroidal one, the launching angle should be adjusted both toroidally and poloidally for optimum O-X conversion. The calculation has shown that the power absorption is strongly Doppler shifted due to the large parallel refractive index caused by the inhomogeneity of the magnetic field. The absorption position is weakly dependent on the electron density and temperature, and it can be controlled by changing the magnetic field strength. The slow X-B heating is also possible by launching the X-mode from the vacuum chamber port located at the low-field side because of the three-dimensional magnetic field structures in heliotron configurations. The accessible window in launching angle is rather wide, and the power absorption can be controlled from on-axis to off-axis, which depends on the launching angle, magnetic field and electron density.