Research of Electron Cyclotron Resonance Heating Methods and Relevant Experiments

For expanding applicable parameter ranges of electron cyclotron resonance heating (ECRH), various methods of ECRH have been studied with use of millimeter-wave sources of 77-, 82.7-, 84-, and 168-GHz gyrotrons in the Large Helical Device (LHD). The fundamental ordinary (O-) mode and the second-harmonic extraordinary (X-) mode are mainly used for starting up, sustaining, and controlling the plasma. Heating efficiencies of ECRH by launching of these modes have been investigated experimentally for wide range of the central electron density and compared with power absorption rates obtained by ray-tracing calculation. ECRH by the third-harmonic X-mode has been performed in each magnetic configuration B_ax = 1 and 2 T with launching of 84-GHz range and 168-GHz millimeter waves. Increases of the electron temperature and the stored energy were observed in both cases. ECRH by the electrostatic electron Bernstein wave (EBW) has been expected to be a promising substitute in parameter ranges where the conventional methods of ECRH by the electromagnetic modes are not available. To perform ECRH by the EBW in LHD, extraordinary-EBW (X-B) and ordinary-extraordinary-EBW (O-X-B) mode conversion processes, the propagation of the wave, and the absorption have been investigated experimentally and theoretically.