Fusion Science and Technology / Volume 53 / Number 1 / January 2008 / Pages 254-260
Technical Note / Special Issue on Electron Cyclotron Wave Physics, Technology, and Applications - Part 2
Electron cyclotron current drive (ECCD) experiments carried out in the TJ-II stellarator are presented. In all the analyzed plasma discharges, the second-harmonic electron cyclotron resonance heating (ECRH) power is launched on-axis from two low-field-side stellarator symmetric positions. To investigate the ECCD properties of the device, the dependence of the total toroidal plasma current on the launching direction of both ECRH beams at fixed density conditions, and on the line average density for some fixed launching configurations, has been determined. In the launching direction scan, only discharges with similar density and temperature profiles have been studied, in order to avoid strong modifications of the bootstrap current contribution and the refraction properties of the plasma. Moreover, the measurements of the toroidal plasma current and the plasma profiles are taken at the end of the discharge, when approximately steady-state conditions are achieved. Using the normalized current drive efficiency as defined by ECCD [identical] <ne> IECCDR/PECRH, we have obtained values up to ECCD [approximately equal to] 0.001 × 1020 A W-1 m-2.