Fast particle experiments in JT-60U

Abstract

Results of fast particle experiments in JT-60U are presented. The fast particles were created with ICRF heating and negative ion based neutral beam injection (N-NBI) heating. With both heating systems Alfvén eigenmodes (AEs) were excited. The AEs that were excited with ICRF during sawtooth stabilization experiments are used to extract information about the magnetic safety profile in the plasma centre. These measurements are compared with motional Stark effect measurements and with sawtooth models. The first results on the radial mode structure of TAEs as measured with an X mode reflectometer system are also given. When the N-NBI beam was injected into a sawtoothing plasma, a significant increase in sawtooth period was observed. A survey is given of the bursting, chirping and stationary frequency modes that have been found in the Alfvén range of frequencies when N-NBI was injected. Most, but not all, of these modes scale with the Alfvén velocity. One group of modes that starts in the continuum and chirps up to the toroidicity induced Alfvén eigenmode (TAE) gap in typically 200 ms can be identified as resonant TAEs, whereas another group of modes appears as short bursts (up to 20 ms) in the Alfvén continuum.