Ion heating experiments have been carried out in the large helical device using ECH (82.5, 84.0, 168 GHz, ≤1 MW), ICRF (38.5 MHz, ≤2.7 MW) and NBI (H° beam: 160 keV, ≤9 MW). The central ion temperature has been observed from the Doppler broadening of Ti XXI (2.61 Å) and Ar XVII (3.95 Å) x-ray lines, which are measured using a newly installed crystal spectrometer with a charge-coupled device. Recently, in ECH discharges, on-axis heating became possible. As a result, a high Te (0) of 6-10 keV and a high ion temperature of 2.2 keV were obtained at ne = 0.6 × 1013 cm-3. A clear increment of Ti was also observed with the enhancement of the electron-ion energy flow when the ECH pulse was added to the NBI discharge. These results demonstrate the feasibility towards ECH ignition. A clear Ti increment was observed also in ICRF discharges at low density ranges of (0.4-0.6) × 1013 cm-3 with appearance of a new operational range of Ti(0) = 2.8 keV > Te(0) = 1.9 keV. In low power ICRF heating (1 MW), the fraction of bulk ion heating is estimated to be 60% of the total ICRF input power, which means Pi > Pe. Higher Ti(0), up to 3.5 keV, was obtained for a combined heating of NBI (≤4 MW) and ICRF (1 MW) at density ranges of (0.5-1.5) × 1013 cm-3. The highest Ti(0) of 5 keV was recorded in Ne NBI discharges at ne ≤ 1 × 1013 cm-3 with the achievement of Ti(0) > Te(0), whereas the Ti(0) remained at relatively low values of 2 keV in H2 and He NBI discharges due to less Pi. The main reasons for the high Ti achievement in the Ne discharges are: (1) 30% increment of deposition power, (2) increase in Pi/ni (five times, Pi/ni ≫ Pe/ne, Pi ≤ Pe) and (3) increase in τei (three times). The obtained Ti(0) data can be plotted by a smooth function of Pi/ni. This result strongly suggests that the ion temperature increases even in the H2 discharge if the Pi can be raised up.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Condensed Matter Physics