On the basis of kinetic description, the analytical formula is derived as an evaluation formula of the energy spectra of fast ion produced by neutral beam injection (NBI) heating. The effects of particle loss due to the loss cone are newly considered in the kinetic equation. The distribution function is derived by integrating the kinetic transport equation as possible as analytical methods. Thus it will be able to reduce a computational time for the systematic analysis of the energy spectra of

more »

... ast ion. The validity of the derived solution is appraised by comparing with the energy spectra experimentally measured by natural diamond detector (NDD) in the Large Helical Device (LHD). Good agreements in their behavior are obtained.