Characterization of Electron Bernstein Wave Emission from the TJ-II Stellarator

Thermal electron emission at 28 GHz has been measured on the TJ-II Stellarator. The microwave emission from over-dense neutral beam heated plasmas, where the plasma density is greater than the ordinary-mode (O-mode) cutoff density (>1.2x1019 m-3), is consistent with electron thermal emission from mode-converted electron Bernstein waves (EBW) via the Bernstein wave to extraordinary mode to ordinary mode scenario (B-X-O). Electron Bernstein wave emission (EBE) measurements are being made to determine the optimum launch angle for planned EBW heating experiments and also to provide an indication of electron temperature evolution in over-dense plasma. A movable focusing mirror located inside the vacuum vessel is used to measure the emission as a function of viewing angle, and measurements are compared with ray-tracing calculations using the TRUBAcode.