Dynamics Of Electrons In Anode Layer Of Hall-type Ion Source

Experimental results of investigations of electron dynamics in anode layer of Hall type ion source ``Radical`` are presented. The ion source consists of plate parallel cathode and anode separated by 4.5mm space. There is ring-like gap in cathode. Inner and outer parts of cathode are the poles of magnetic circuit which produces lateral magnetic field H = 0.7 {divided_by} 2 kE. Anode voltage U{sub a} was 0.6 {divided_by} 2 kV, pressure in discharge space was about 10{sup {minus}3} Tor. Glow cathode which might be moved in axial direction was used to investigate electron dynamics. Study of emission current distribution between the electrodes by additional electron injection had shown that only electrons from anode-cathode spacing are able to reach the anode. Dependence of emission current vs. distance between anode and emitter Z correlates with plasma potential distribution. The phenomenon of electron escape to cathode is interesting because even applying of cut-off bias at the emitter does not lead to vanishing of electron current. In addition, electron currents (about 10% of anode current) on cathode exists without external injection of electrons. There is considerable asymmetry of current distribution between inner and outer parts of the cathode. Energoanalysis of the escaping electrons hadmore » shown that electron loss was due to population through high energy tail of distribution function, which appeared as a result of electron-electron collisions.« less