MEASUREMENT OF HIGH ENERGY PROTON TEMPERATURE IN LHD

摘要

Measurement of energetic ion spectra has been one of the key diagnostics in fusion plasma experiment. Among various methods, passive measurement of fast neutrals escaping from magnetically confined plasma is widely used. In order to derive ion spectra, possible all neutralization processes and spatial distribution of each particle spices responsible for these processes should be carefully considered and the measured spectra should be modified by sum of these energy-dependent charge exchange probabilities. In a burning plasma experiment, the ion spices are hydrogen isotopes, helium isotopes and impurities, and H~0(D~0/T~0), He~0, He~+ , A~(q+) (q < Z) are responsible for neutralization of protons. Helium concentration will be high in a D~3He plasma and will be low in a DT plasma. In Large Helical Device (LHD), most of ICRF sustained, or ICRF assisted discharges are produced by He+H admixture. A code to calculate H~0, He~0, He~+ distribution, including 6 charge exchange processes, electron/ion impact ionization and recombination processes in plasma of cylindrical geometry has recently been developed (ACHEN-Code). Using these results and charge-exchange cross sections, proton energy spectra and energetic tail temperatures (T_(eff)) of two vertical veiwing chords of LHD are derived from the neutral spectra measured by Natural Diamond Detectors (NDD). With the help of ACHEN-Code, not only the T_(eff), but also the information on the neutral influx can be obtained from the calibrated NDD counting rates, and that on the neutral source temperature can be obtianed from the comparison of T_(eff) of the two vertical chord in poloidal cross section.