Ion Transport in Real and Velocity Space and Confinement in the GAMMA 10 Tandem Mirror.

Abstract

Loss regions in the plasma particles' velocity space are decreased by the electrostatic potentials created on both sides of the plasma, which results in the improvement of the axial confinement in the tandem mirror. We found experimentally that the ion loss region was in contact mainly with both a plug potential bounce region and the outer mirror throat bounce region in which ions were bounced near the outer mirror throat of the plug/barrier cell. These bounce ions play an important role in tandem mirror confinement. The outer mirror throat bounce region is caused by the relatively high potential in the neighborhood of the outer mirror throat. The core plasma's radial potential profile was controlled by changing the potential of coaxially separated end plates, and it was found that control of the radial potential profile was useful for retardation of the radial loss of the bounce ions. We observed a hump structure on the energy distribution function of the end-loss ions, and found that the enhancement of the end-loss ions was caused by ion flow from the trapped region to the loss region due to Alfvn Ion Cyclotron (AIC) fluctuations. Although the ion diffusion due to the fluctuations enhances the axial ion loss, the axial loss can be reduced by creation of a higher confining potential.