Gentle hump structure on energy spectra of end-loss ions was observed in the RF driven tandem mirror plasma by use of an end-loss energy component analyzer (ELECA), which has been developed in order to directly measure velocity distribution functions of the end-loss ions.1 Ions are heated anisotropically in the central cell of the tandem mirror by the ICRF wave injection, and Alfvén ion-cyclotron (AIC) fluctuations are excited due to the anisotropic ion temperature.2 The correlation between the hump structure and the excitation of the AIC fluctuations was observed experimentally. From the viewpoints of the heating characteristics and the resonance condition, the hump energy was estimated and successfully compared with the experimetal results. Influence of the ICRF waves on the hump structure was investigated using a bounce averaged Fokker Planck code.3 The AIC fluctuations enhance the end-loss ions scattered from the trapped region to the loss region, and have direct effects upon the ion confinement. The energy flux of the enhanced end-loss ions due to the AIC fluctuations was estimated and the enhancement factor was obtained. The strong anisotropic ion heating is dangerous for the ion confinement in the open systems which contain necessarily the loss regions.
