The theoretical properties of electron Bernstein wave (EBW) plasma heating in the TJ-II stellarator are presented in this work. Previous studies carried out in this device have demonstrated that the O–X–B mode conversion at the fundamental electron cyclotron harmonic is the best scenario for plasma heating. This scheme presents high absorbed power for central densities above 1.2 × 1019 m−3 and has no upper density limit. In this paper, the ray tracing code TRUBA has been used in its non-relativistic modality to optimize the power injection position and to design a launching system that provides the optimum theoretical results. The main characteristics of the system, whose final design is based on the former calculations, are described. To explore the importance of relativistic effects and to compare them with the non-relativistic calculations, the weakly relativistic dispersion relation, valid for and thus suitable for EBW at low cyclotron harmonics, has been obtained and included in TRUBA. Although they are of little importance for the optimization calculations, the relativistic effects are shown to be not negligible both in the ray trajectories and in the power absorption estimations for temperatures above 1 keV.
Absorption of fast waves excited by a phased four-loop antenna array in the JFT-2M tokamak