Charge exchange spectroscopy measurements of ion temperature and toroidal rotation in JET

Abstract

The JET tokamak relies on an active charge exchange spectroscopy diagnostic for measurements of ion temperature, toroidal rotation velocity and impurity density profiles. It uses the neutral heating beams as diagnostic beams and provides measurements at eight to twelve radial positions simultaneously with a time resolution of about 100 ms. A description of the instrument is given, together with an analysis of the experimental data and an account of recent results. Profiles of ion temperature and rotation frequency, based on the carbon C VI n = 8 to n = 7 transition at 5290.5 Å, are presented for plasmas in the hot ion mode, for magnetic limiter plasmas, and for discharges where a locked MHD mode brings the plasma to rest despite continued neutral beam injection. H-mode to L-mode transitions are found to cause a collapse of the edge ion temperature and the toroidal rotation frequency within less than a sampling time of 12 ms. This time resolution is also sufficient to reveal ion heat pulses following sawtooth crashes.