Two-Dimensional Studies of Electron Bernstein Wave Emission in MAST

Abstract

Angular scanning of electron Bernstein wave emission (EBE) has been conducted in MAST. From EBE measurements over a range of viewing angles, the angular position and orientation of the B-X-O mode conversion (MC) window can be estimated, giving the pitch angle of the magnetic field in the MC layer. The radial position of the corresponding MC layer is found from Thomson scattering measurements. Measurements at several frequencies can provide a pitch angle profile. Results of pitch angle profile reconstruction from EBE measurements are presented in comparison with motional Stark effect measurements. Microwave imaging of the B-X-O MC window is proposed as an alternative to angular scanning. The proposed scheme is based on an imaging phased array of antennas allowing the required angular resolution. Image acquisition time is much shorter than magnetohydrodynamic (MHD) time scales so the EBE imaging can be used for pitch angle measurements even in the presence of MHD activity.