Magnetic configuration effects on fast ion losses induced by fast ion driven toroidal Alfvén eigenmodes in the large helical device

Beam-ion losses induced by fast-ion-driven toroidal Alfvén eigenmodes (TAE) were measured with a scintillator-based lost fast-ion probe (SLIP) in the large helical device (LHD). The SLIP gave simultaneously the energy E and the pitch angle χ = arccos(υ _///υ) distribution of the lost fast ions. The loss fluxes were investigated for three typical magnetic configurations of R _ax-vac = 3.60 m, 3.75 m, and 3.90 m, where R _ax-vac is the magnetic axis position of the vacuum field. Dominant losses induced by TAEs in these three configurations were observed in the E/χ regions of 50∼190 keV/40°, 40∼170 keV/25°, and 30∼190 keV/30°, respectively. Lost-ion fluxes induced by TAEs depend clearly on the amplitude of TAE magnetic fluctuations, R _ax-vac and the toroidal field strength B _t. The increment of the loss fluxes has the dependence of (b _TAE/B _t) ^s. The power s increases from s = 1 to 3 with the increase of the magnetic axis position in finite beta plasmas.