Charge exchange spectroscopy results of JET neutral helium beam heating experiments

Helium beam fuelling experiments provide an ideal test bed for the investigation of slowing-down low energy alpha particles (<145 keV) and their velocity distribution functions as well as their radial distribution. Considerable progress has been achieved in the modelling of the expected charge exchange spectra observed parallel and perpendicular to the magnetic field and the development of suitable spectral analysis procedures. The first full analysis of radial profiles of temperature and slowing-down and thermalised alpha particle densities has however revealed several puzzling results, such as anisotropic ion temperatures and phase differences in the sawtooth oscillation of fast and thermal particles which require intense future modelling efforts. (author) 3 refs., 7 figs