Fast-time-resolution charge-exchange measurements during the ‘fishbone’ instability in the poloidal divertor experiment

Measurements of fast-ion losses due to the ‘fishbone’ instability during high-β_Tq neutral-beam-heated discharges in the Poloidal Divertor Experiment have been made using two new vertical-viewing charge-exchange analysers. The measurements show that the instability has an n = 1 toroidal mode number, and that it ejects beam ions in a toroidally rotating bacon directed outward along a major radius. Observations of ejected ions with energies up to twice the beam injection energy at R ≈ R_o + a indicate the presence of a non-µ-conserving acceleration mechanism.