Exact treatment of charge exchange loss in beam driven currents

A two-dimensional fast ion Fokker-Planck equation is analytically solved with a new cross-section formula for charge exchange loss. The new formula includes the exact cross-section dependence on ion energy and is valid from 2 keV up to several hundred keV, where charge exchange is always negligible. A loss of beam driven currents due to the charge exchange has been analysed, using this analytic solution of Fokker-Planck equation. It has been revealed that the previous rough treatment with the charge exchange cross-section, proportional to 1/ nu , sometimes results in a considerable error. By a systematic parametric survey, the reduction rates for beam driven currents, due to charge exchange loss, are rearranged and tabled. Also, a reduction in global current drive efficiency by charge exchange in a next generation Tokamak is briefly discussed.