Fusion Science and Technology / Volume 52 / Number 2 / August 2007 / Pages 134-144
Technical Paper / Electron Cyclotron Wave Physics, Technology, and Applications - Part 1
A review of recent experimental results in electron cyclotron (EC) resonance heating and EC current drive (CD) (ECCD) is given. Special emphasis is put on the recent developments of new schemes in which EC waves can heat and drive current in magnetically confined fusion plasmas. These comprise scenarios to overcome the density cutoff experienced in application of the classical first-harmonic ordinary mode (O1) and second-harmonic extraordinary mode (X2) schemes as well as to increase the CD efficiency of EC waves while maintaining their good localization. In particular, we discuss recent experimental progress in tokamaks, stellarators, and spherical tori in the areas of the second-harmonic ordinary mode (O2), third-harmonic extraordinary mode (X3), and electron Bernstein wave schemes [mostly Ordinary-eXtraordinary-Bernstein (O-X-B) scheme] as well as experiments in which the combination of ECCD with lower hybrid CD leads to a synergetic increase of the ECCD efficiency. A particular application of ECCD that has recently received much attention and is therefore reviewed in this paper is the suppression of neoclassical tearing modes (NTMs) by ECCD. We show that the theoretically predicted requirements for ECCD in terms of deposition (maximizing the ECCD driven current density) and injection in phase with the O-point of the magnetic island associated with the NTM (which is needed when the island width falls below the deposition width) have been verified experimentally. Also, many of the elements needed for constructing a reliable, feedback-controlled NTM suppression system for ITER based on ECCD have now been demonstrated experimentally, and the next step, which is their integration into a reliable scheme, is well within reach.