Evaluation of Fast-Ion Confinement Using a Radially Injected Neutral Beam in the LHD

抄録

The confinement properties of perpendicular fast ions, which have kinetic energies mostly perpendicular to magnetic field lines, are investigated in the Large Helical Device (LHD) using short pulse injections of neutral beams (NB). Fast-ion lifetimes are evaluated using the fast neutral decay times after NB turn-off, where the neutrals are measured by an array of silicon-diode fast neutral analyzers. We found that the lifetime normalized by the 90-degree pitch-angle scattering time can be used as a scale of fast-ion confinement properties in magnetically confined fusion devices. The good confinement properties of the LHD's inwardly shifted configuration were demonstrated using the evaluated normalized lifetimes.