AbstractIn the Heliotron E device, fast ion slowing-down processes (deceleration, parallel diffusion, and pitch angle scattering) and the particle loss process are investigated by the measurement temporal behaviour of charge-exchange energy spectra during neutral beam injection (NBI). Using electron cyclotron resonance heating (ECRH), two effects are studied with respect to: (1) extrapolation of slowing-down behaviour to a longer slowing-down time and (2) modification of the ion loss associated with the radial electric field. It is found that (1) there are discrepancies :in the theoretical value in the deceleration and the parallel diffusion processes in NBI + ECRH and ECRH plasmas, and that (2) the particle loss is reduced by the use of ECRH on the NBI plasma.