Magnetic configuration effects on fast ion losses induced by fast ion driven toroidal Alfven eigenmodes in the Large Helical Device

Beam ion losses induced by fast-ion driven magnetohydrodynamic (MHD) instabilities i.e. toroidal Alfven eigenmode (TAE) are measured with a scintillator-based lost-fast ion probe (SLIP) on various magnetic configurations of the large helical device (LHD). Dependence of the loss fluxes where the energy E and pitch angle χ=arccos(νsub(parallel)/ν) distribution of the lost fast ions are simultaneously resolved on the magnetic axis position of the vacuum field Raxvac have been investigated in three typical magnetic configurations of Raxvac =3.60 m, 3.75 m, and 3.90 m. Dominant losses induced by TAEs were observed in E/χ ∼50-190 keV/∼40deg, ∼40-170 keV/∼25deg, and ∼30-190 keV/∼30deg region for the configurations of Raxvac=3.60 m, 3.75 m, and 3.90 m, respectively. Lost ion fluxes induced by TAEs clearly depend on the amplitude of TAE magnetic fluctuations, Raxvac and the toroidal field strength Bt. The losses increase, having the dependence of (bTAE/Bt)s. The power s changes from s=1 to 3 with the increase of the magnetic axis position in finite beta plasmas. (author)