Electron Bernstein waves emission in the TJ-II Stellarator

TL;DR

This paper presents the development and testing of an electron Bernstein emission diagnostic in the TJ-II stellarator, providing insights into wave conversion processes and radiation properties relevant for plasma heating.

Contribution

It introduces a new EBE diagnostic system integrated with EBW heating, and compares theoretical predictions with experimental data to understand wave conversion in the stellarator.

Findings

Identification of the O-X mode conversion window

Evidence of B-X-O conversion process through polarization analysis

Correlation between theoretical models and experimental EBE data

Abstract

Taking advantage of the electron Bernstein waves heating (EBWH) system of the TJ-II stellarator, an electron Bernstein emission (EBE) diagnostic was installed. Its purpose is to investigate the B-X-O radiation properties in the zone where optimum theoretical EBW coupling is predicted. An internal movable mirror shared by both systems allows us to collect the EBE radiation along the same line of sight that is used for EBW heating. The theoretical EBE has been calculated for different orientations of the internal mirror using the TRUBA code as ray tracer. A comparison with experimental data obtained in NBI discharges is carried out. The results provide a valuable information regarding the experimental O-X mode conversion window expected in the EBW heating experiments. Furthermore, the characterization of the radiation polarization shows evidence of the underlying B-X-O conversion process.