Redistribution of ICRH Fast Ions in the Presence of Fishbones and Alfvén Eigenmodes
A set of experiments on fast ion redistribution was carried out in recent JET campaigns, in which the new fast ion loss detectors were used for the first time. This paper reports on the experiments carried out with low density plasmas and high ICRH power, a scenario that allow large populations of highly energetic fast ions to be built up and a variety of instabilities to be destabilized. Fast ion losses were successfully measured and it could be confirmed they were effectively associated to MHD activity. Losses occurred at considerably high energies (of the order of few MeV) and two types of fast ions were identified by the gamma-ray diagnostics: fast protons with an energetic tail in excess of 4.5MeV due to ICRH tuned to a fundamental H-resonance in the centre of the plasmas and D-ions accelerated with second harmonic heating whose energies exceeded 0.5MeV. Three types of losses were identified, one associated with sawtooth crashes, one associated with TAE and high frequency fishbones and a third group that seems to correlate with tornado modes. When tornado modes became unstable, a significant increase in the number of losses was measured and a change in both the energy and pitch angle of the lost ions was observed. In addition, it was also observed that the number of losses increased significantly with the ICRH power.