Analysis of the loading resistance for ICRF heating experiments in ASDEX

The loading resistance has been analyzed for ICRF heating experiments in ASDEX plasmas, and some interesting features have been observed regarding the loading resistance in three particular cases. (1) In H-minority heating experiments, the loading resistance decreases sharply at the L-H transition. However, during the H-phase, which lasts for a few hundred milliseconds, the increasing density induces a variation in the loading resistance. This is reasonably accounted for in terms of an eigenmode effect, and is in agreement with theoretical predictions. (2) In long-pulse second-harmonic heating experiments a slowly changing isotope concentration (H concentration from 70% to 85%) is accompanied by a gradual decrease in loading resistance. (3) In 2 Omega CH heating experiments with repetitive pellet refueling, in which two confinement phases have been identified, it has been observed that the temporal behaviour of the loading resistance is quite different for the two phases.