ICRF heating of currentless plasma in Heliotron E

High power and long pulse ICRF heating of a currentless plasma is carried out in Heliotron E. Three kinds of wave mode are studied in a wide range of plasma parameters. Fast wave (minority heating), ion Bernstein wave and slow wave (ion cyclotron wave) heatings are performed by using the same antenna system, while gas species, electron density and magnetic field strength are varied. With the fast wave heating, the ion temperature increases from 200 eV to 650 eV at an electron density of 2.2x1019m-3. The duration of effective heating is, however, limited to less than 50 ms, because of the rapid increase in radiation loss power. Carbonization of the vacuum chamber reduces the radiation loss power to about 30%, and then the plasma which has been initiated by an ECH pulse is effectively heated and sustained by ICRF pulse for 100 ms only. The behaviour of the antenna loading resistance is studied in comparison with a theoretical analysis. The fundamental cavity mode is clearly identified. With ion Bernstein wave heating, the ion energy spectrum has a two component form. The effective ion temperature in the perpendicular direction increases quickly during the ICRF pulse of a frequency of 4 ωcD. With slow wave heating, the ion temperature increases up to 1.6 keV at an electron density of 0.6x1019m-3. The heating efficiency depends strongly on the electron density. (author)