ICRF heating of currentless plasma in Heliotron E

In the Heliotron E device, a non-axisymmetric helical system, ICRF heating experiments were carried out for the first time, using fast-mode and slow-mode waves. In the fast-wave heating experiment, ICRF power of up to 550 kW was emitted during 15 ms by four antenna loops. Effective heating of a current-less ECRH-produced target plasma was observed over a wide density range. The plasma loading resistance of an antenna loop reached about 5 Ω. This is a value comparable with that of tokamak experiments. The increments of ion and electron temperatures by fast-wave heating were about 200–230 eV at an electron density of about 3 × 1019m−3. Minority heating and pure second-harmonic heating have almost the same efficiency ((1–2) × 1019eV·m−3·kW−1) during the short RF pulse used (t ≤ 15 ms). The energy transfer rate from the waves to ions and electrons could be explained by mode conversion. The signals of toroidal eigen-modes were experimentally observed and radial mode numbers could be determined using a simple model. In the slow-wave heating experiment, the upper density limit of effective heating appeared to be in qualitative agreement with wave theory.