Disruptions are a major operational concern for next generation tokamaks, including ITER. They may generate excessive heat loads on plasma facing components, large electromagnetic forces in the machine structures and several MA of multi-MeV runaway electrons. A more complete understanding of the runaway generation processes and methods to suppress them is necessary to ensure safe and reliable operation of future tokamaks. Runaway electrons were studied at JET-ILW showing that their generation dependencies (accelerating electric field, avalanche critical field, toroidal field, MHD fluctuations) are in agreement with current theories.

The confinement of fast particles is of crucial importance for the success of future burning plasma experiments.. On JET, the confinement of ICRF accelerated fast hydrogen ions with energies exceeding 5 MeV has been measured using the characteristic γ-rays emitted through their inelastic scattering with carbon impurities, 12 C(p,p'γ) 12 C. Recent experiments have shown a significant decrease in this γ-ray emission (by a factor of 2) during so-called tornado mode activity (core-localised TAEs within the q = 1 surface) in sawtoothing plasmas. This is indicative of a significant loss or extensive re-distribution of these (> 5 MeV) particles from the plasma core. In this paper, mechanisms responsible for the radial transport and loss of these fast ions are investigated and identified using the HAGIS code, which describes the interaction of the fast ions and the TAE observed. The calculations show that the overlap of wave-particle resonances in phase-space leads to an enhanced radial transport and loss. On both JET and ASDEX Upgrade, new fast ion loss detectors have been installed to further investigate the loss of such particles. On JET, fast ion loss detectors based around an array of Faraday cups and a scintillator probe have been installed as part of a suite of diagnostic enhancements. On ASDEX Upgrade, a new fast ion loss detector has been mounted on the mid-plane manipulator allowing high resolution measurements in pitch angle, energy and time. This has enabled the direct observation of fast ion losses during various MHD phenomena to be studied in detail. ELM induced fast ion losses have been directly observed along with the enhancement of fast ion losses from specific areas of phase-space in the presence of NTMs and TAEs.