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-βsub(T)q 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 beacon directed outward along a major radius. Observations of ejected ions with energies up to twice the beam injection energy at R approx.= R0+a indicate the presence of a non-μ-conserving acceleration mechanism. (author)