Fast particles in JET plasmas

Experimental observations on fast particles in JET plasmas will be reviewed and new results presented. A description of the diagnostics used will be given. Up to 3 MJ of fast particles in the MeV range have been created using the RF minority heating system. So far little or no evidence has been found for anomalous loss of fast particles. From the instabilities predicted to affect fast particles only sawteeth and fishbones have been seen to influence their behaviour. Previous observations showing the redistribution of fast particles in the plasma during sawtooth crashes are confirmed. The loss of a small fraction of high energy particles (MeV range) is now observed rather regularly. On a few occasions, when fishbone-like events were observed, these did not seem to influence the fusion reactivity except for one event reported earlier. The burn-up of tritons generated in the second branch of the dd reaction appears to be classical with maybe one or two exceptions. For the first time the localisation of fast particles during RF heating has been achieved. The measurement of neutron spectra during additional heating shows a strong anisotropy in agreement with model calculations. The same anisotropy is expected for alpha particles from a driven system, a fact normally not taken into account in theoretical investigations. Figs