The character of ions motion in a plasma in crossed fields at the generation of ion cyclotron oscillations

Summary form only given. A low density discharge (n/spl sim/10/sup 9+10/ sm/sup -3/) in crossed longitudinal magnetic field and radial electric field with a Penning electrodes configuration was experimentally studied. It´s known that a resonance generation of eigen ion-cyclotron oscillations is possible in such a discharge when duplicate frequency of ions motion in crossed fields is about equal to the ion gyrofrequency. The generation occurs in a narrow axially symmetric layer. The resonance condition defines an electric field value in the region of instability generation in a plasma at given magnetic field as well as the character of the motion of resonance ions. In experiments the generation of ion-cyclotron oscillations was observed in spatial regions of the discharge, where the electric field exceeded the resonant value many times. In the framework of existing theoretical models strong electric fields must lead to radial ion oscillations and to the absence of cyclotron oscillations generation. Using experimental data we carried out numerical simulations of ion motion in regions of their appearance near turning points in crossed fields at different shapes of a plasma potential distribution. Transversal energy spectra of particles were obtained experimentally. The phenomenological model allows one to explain conditions of ion-cyclotron instability generation.