Energetic tail formation by ion-cyclotron-range-of-frequencies (ICRF) heating
was studied in the large helical device (LHD), by measuring
high-energy charge-exchange atom spectra with a specially developed natural
diamond detector, which views the LHD plasma perpendicularly.
Comparison of measured effective perpendicular temperature of ICRF-driven
H+ minority ions with the classical Stix model indicates that
perpendicular ions with energy at least up to 150 keV are well confined in
the centre region of the LHD. However, deviation from the classical
prediction was observed for high-energy perpendicular protons in the outer
region of the plasma, indicating ripple-induced transport and
charge-exchange losses. With perpendicular fast atom spectrum and flux
measurements, small yet notable differences were detected co-injected and
counter-injected ICRF-driven beam ion confinement during combined
neutral beam injection (NBI) and
ICRF heating. These results can be explained by the differences in the orbit
topology and ICRF-induced drift.
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