Electron cyclotron heating and current drive in the TJ-II stellarator

Electron cyclotron resonance heating (ECRH) has become an attractive technique in today's fusion experiments not only as a heating mechanism but also as a diagnostic tool and a way to induce controllable currents through electron cyclotron current drive (ECCD). In this paper we show, using ray tracing simulations, how one can address all these issues with the ECRH system designed for the TJ-II stellarator. This ECRH set up consists of two 500 kW gyrotrons at f = 53.2 Ghz coupled to the plasma through two quasi-optical transmission lines, placed at two stellarator symmetric positions, and equipped with an internal steerable mirror. Using the three-dimensional (3D) Hamiltonian ray tracing code, TRECE, almost full single-pass absorption with localized power deposition is found for both on- and off-axis heating for any magnetic configuration. The simulations also show that it is possible to induce an appreciable ECCD despite the small oblique incidence angles attainable with the movable mirrors because of the rapid variation of the magnetic field direction and strength with the toroidal angle in TJ-II.