A Study of RF Power Absorption Mechanisms in JET ICWC Plasmas

This paper focuses on further study of the RF power absorption mechanisms responsible for Ion Cyclotron Wall Conditioning (ICWC) discharge ignition and sustainment in fusion machines in the presence of high toroidal magnetic field. The dominant electron collisional and also ion collisional and cyclotron absorption mechanisms are analyzed during local (antenna-near) gas breakdown (wpe < w) and over-torus plasma wave excitation (wpe > w) phases of RF discharge. Optimization of the absorbed RF power in terms of (i) Ez-field generation (along BT-field lines), (ii) antenna phasing and (iii) waves excitation in plasmas with multi-ion species resulted in a successful performance of the JET ICWC experiments (BT = 3.3 T, f = 25MHz) using the standard ICRF A2 antennas in a scenario envisaged at ITER full field (BT =5.3T, f =40MHz): on-axis fundamental ICR for deuterons, w = wcD+.
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