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

Electron cyclotron resonance heating (ECRH) has become an attractive techni que 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 elec tron cyclotron current drive (ECCD). In this paper we show, using ray traci ng simulations, how one can address all these issues with the ECRH system d esigned 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 t ransmission lines, placed at two stellarator symmetric positions, and equip ped with an internal steerable mirror. Using the three-dimensional (3D) Ham iltonian ray tracing code, TRECE, almost full single-pass absorption with l ocalized power deposition is found for both on- and off-axis heating for an y magnetic configuration. The simulations also show that it is possible to induce an appreciable ECCD despite the small oblique incidence angles attai nable with the movable mirrors because of the rapid variation of the magnet ic field direction and strength with the toroidal angle in TJ-II.