The Design of an Electron Bernstein Wave Heating System for the TJ-II Stellarator

Electron Bernstein waves excited by either X-B or O-X-B conversion scheme can be used to create and heat a dense plasma in TJ-II in the first harmonic. Two gyrotrons operating in the regime of second-harmonic electron cyclotron resonance heating (53.2 GHz) create a target plasma, and then a 28-GHz gyrotron is switched on. The power of the gyrotron is 300 kW and the pulse length is 100 ms. A new high-voltage power supply was designed for this gyrotron. It supplies 70 kV and a maximum current of 25 A. Corrugated waveguides will be used to transmit the microwave radiation. The distance between the position of the gyrotron and the TJ-II window is ~7 m. The microwave beam is launched through the D6 port of TJ-II. A movable internal mirror is needed to focus the beam and to accomplish the restrictive launching angle conditions. The layout and the main features of the new system are presented.