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 Alfven 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(v///v) distribution of the lost fast ions. The loss fluxes were investigated for three typical magnetic configurations of Rax_vac=3.60 m, 3.75 m, and 3.90 m, where Rax_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, Rax_vac and the toroidal field strength Bt. The increment of the loss fluxes has the dependence of (bTAE/Bt)s. The power s increases from s=1 to 3 with the increase of the magnetic axis position in finite beta plasmas.