AbstractThe charge exchange energy spectrum of beam ions is analyzed in order to study the fast ion confinement. The spectrum is observed to have a depletion, and the effects of the magnetic field, B0 and radial electric field, Er, induced losses on the depletion structures are discussed. Relaxation oscillations of the spectrum are found and a time varying Er is considered to interpret them. A reduction of the depletion structure is observed with electron cyclotron resonance heating (ECRH), and is discussed with the edge Er change and improved ion heating.