Experimental Investigation of the Fast Ion Orbit Shift and Loss Cone in Heliotron E

The inward shift and the toroidal precession of the deeply trapped ion orbit in Heliotron E plasmas are measured using the charge exchange analysis, and found to be consistent with the classical drift orbit theory. Depletion structures on energy spectra are observed during limiter insertion or pellet injection. Furthermore, the rapid change of the depletion structures by additional beam injection or limiter bias is also investigated. These depletion structures can be explained by an effect of the resonant loss due to the negative radial electric field, E r . Theoretical analysis of the E r profile shows that a positive E r in the vicinity of the loss boundary disturbs the resonant condition of deeply trapped particles locally, and can reduce the resonant loss cone.