Investigation of Experimental Configuration for Electron Bernstein Wave Heating on LHD

Abstract

Investigation of experimental configuration for the electron Bernstein wave (EBW) heating by using the existing electron cyclotron heating (ECH) antennas on LHD was performed. By using an antenna installed in the lower port, direct oblique launching of the extraordinary (X-) mode from the high magnetic field side (HFS) is available. Since the parallel component of the refractive index (N||) varies during propagation because of the inhomogeneity of the magnetic field, N|| can be zero when the launched X-mode crosses the fundamental electron cyclotron resonance (ECR) layer even N|| is noonzero initially. In such a condition, if the electron density is above a certain level the obliquely launched X-mode can pass the fundamental ECR layer without being damped out and can be mode-converted to EBW that is absorbed at the Doppler shifted ECR layer. By using an antenna installed in the horizontal port, oblique launching from the lower magnetic field side (LFS) toward the over-dense plasma is available. Excitation of EBW via the mode conversion process of ordinary mode(O)-extraordinary mode(X)-electron Bernstein wave (B) is expected with the O-mode launching toward an appropriate direction. The O-X-B mode conversion rate and the region of power deposition were surveyed by varying the magnetic field strength and the launching direction. The results of the survey suggest that efficient heating in the core region is difficult by using the existing antenna. Rearrangement of the final mirror of the launching antenna may be needed.