Behaviour of ion temperature in electron and ion heating regimes observed with ECH, NBI and ICRF discharges of LHD

Abstract

Ion temperature at the plasma centre has been measured from Doppler broadening of Ti XXI (2.61 Å) and Ar XVII (3.95 Å) x-ray lines using a newly installed crystal spectrometer with CCD detector in ECH, NBI and ICRF plasmas of Large Helical Device (LHD). The ion temperature obtained in a range of 0.6 and 3.5 keV was analysed with electron density and compared with electron temperature. A new parameter range of Ti>Te was found in low-density (ne<1013 cm−3) H-minority ICRF discharges operated in the ion-heating regime (Pi⩾Pe), whereas the ion temperature was roughly equal to the electron temperature in NBI discharges operated in the electron-heating regime (Pi<Pe). The ion temperature in the ICRF and ICRF + NBI discharges was correlated with the input power to bulk ions over the ion density (Pi/ni). As a result, a good correlation was obtained between them and it also indicated a clear rise of the ion temperature for the increasing Pi in a range of Pi/ni<5 (MW/1013 cm−3).