Observation of gentle hump structure on energy distribution functions of end-loss ions in the rf-driven tandem mirror plasma

A gentle hump structure on energy distribution function of end-loss ions wa s observed in the rf-driven tandem mirror plasma by use of an end-loss ener gy component analyzer. Alfven ion-cyclotron (AIC) fluctuations are excited spontaneously due to anisotropic ion heating in the central cell of the tan dem mirror. We observed that the excitation of the AIC waves caused the hum p structure on the energy distribution function. The enhancement factor of the end-loss ions is estimated, and the gentle hump structure is discussed from the viewpoint of the heating characteristics of the AIC waves. It is p ointed out that the hump structure decreases the ion confinement.