The sloshing-ion density distribution is produced in one of the minimum-^ mirrors of GAMMA 6 by injection of neutral beams at 62° to the axis. The formation of sloshing ions is confirmed by pitch-angle distributions measured with secondary emission detector arrays and a gridded energy analyzer. A dip of plasma potential is observed associated with the density minimum of the sloshing-ion distribution.

A Monte Carlo simulation on sloshing ion formation and the associated potential dip is described. It is shown in the GAMMA 6 tandem mirror machine that the sloshing ion distribution can be sustained for about 500 µs. The warm passing ions have a density depression in the region of the sloshing-ion density dip because of the acceleration due to the potential. This effect is included in the evaluation of the potential dip self-consistently. The potential dip is sustained for the duration of sloshing ion formation because the trapped cold ions obtain energy from the passing ions and escape from the potential dip.

As a step towards the creation of a thermal barrier in a tandem mirror, formation of sloshing ion distribution is studied by oblique injection of neutral beams into one of the minimum B mirrors of GAMMA 6. Formation of the sloshing ion distribution is verified from the observations of the pitch angle distribution. The distribution is kept in a quasi-steady state, against relaxation of sloshing ions, to form a broad distribution. Potential dip is also observed in association with the sloshing ion distribution. The potential dip is sustained because the density of cold ions trapped in the dip is small.