The purpose of this work is to reveal the effects of the energetic particle mode (EPM) on fast-ion transport and consequent fast-ion loss in the compact helical system (CHS). For this purpose, fast particle diagnostics capable of following fast events originating from the EPM (f < 100 kHz) and from the toroidicity-induced Alfvén eigenmode (TAE) (f = 100–200 kHz) are employed in CHS. Experiments show that the EPM excited by co-circulating fast ions in an outward-shifted configuration is identified as a mode of m/n = 3/2 and can enhance fast-ion loss when its magnetic fluctuation amplitude exceeds ∼4 × 10−5 T at the magnetic probe position. The lost fast-ion probe (LIP) located at the outboard side of the torus indicates that bursting EPMs lead to periodically enhanced losses of co-going fast ions having smaller pitch angles in addition to losses of marginally co-passing fast ions. Coinciding with EPM bursts, the Hα light detector viewing the peripheral region at the outboard side also shows large pulsed increases similar to that of the LIP whereas the detector viewing the peripheral region at the inboard side does not. This is also evidence that fast ions are expelled to the outboard side due to the EPM. The charge-exchange neutral particle analyser indicates that only fast ions whose energy is close to the beam injection energy Eb are strongly affected by EPM, suggesting in turn that observed EPMs are excited by fast ions having energy close to Eb.
Velocity space resolved absolute measurement of fast ion losses induced by a tearing mode in the ASDEX Upgrade tokamak