Instabilities and confinement of fast particles on JET and MAST

Measurements and understanding of confinement of fast particles and instabilities driven by fast particles are crucial for successful operation of next-step burning plasma machines. Energetic ion confinement and losses and energetic ion-driven instabilities were investigated in experiments on JET and on MAST with a wide range of new diagnostics, in conventional and shear-reversed plasmas, exploring a wide range of effects. In JET experiments, renewed X-mode reflectometry, FIR interferometry, new lost ion scintillator and Faraday cups, complementary to Mirnov coils, 0-mode interferometry, gamma-ray and NPA diagnostics, provide a consistent set of data on fast ion evolution in the presence of fast-ion driven instabilities. The higher quality new data on, e.g. 'tornado' modes in monster sawteeth discharges and on Alfven Cascades (ACs) in reversed-shear discharges, reveal more comprehensively and with a better time resolution the effects of fast-ion driven instabilities on fast ion losses and confinement. Higher sensitivity and better time resolution of interferometry techniques now allowing detection of ACs in JET plasmas with more than 30 MW of input power made possible to employ Alfven spectroscopy based on ACs in such discharges. The renewed X-mode reflectometry provides now information on the AC localisation region, allowing determination of the qmin evolution in space and time and facilitating the development of ITB scenarios. Alfven spectroscopy aiming at kinetic information on electron and ion pressures, as well as the use of sub-Alfvenic NBI for exciting ACs is reviewed. TAEs, ACs, high-frequency modes, and chirping modes are excited by super-Alfvenic NBI in MAST discharges. The super-Alfvenic NBI makes MAST a good test bed for testing diagnostics for Alfven instabilities. MAST is now equipped with magnetic coils with frequency range up to 5 MHz, soft X-ray camera with frequency range up to 250 kHz, and multi-channel (in energy and in lines-of-sight) NPA. The roles which the various types of energetic particle driven modes play at different values of thermal plasma beta are reviewed. In order to further investigate the effects of very high beta on Alfven instabilities, such as the suppression of core-localised TAEs by plasma pressure gradient, new TAE antennas are being installed in MAST. Progress in deploying the TAE antennas for detection and evaluation of TAE-resonances will be reviewed. Modelling of energetic ion-driven instabilities with the HAGIS and CASTOR-K codes will be presented. (author)