Anisotropy of Ion Emission from a Low Energy Plasma Focus

Abstract

We have investigated the ion flux, ion energy and anisotropy of carbon ion emission, at different angular positions, from a low energy Plasma Focus (PF) device, operating in methane, at 20 kV, with 1.8 kJ stored energy. A detector array is used to measure simultaneously the ion beams at five different angles with respect to the PF axis (0°, 10°, 15°, 20° and 90°), at a distance of 77 cm from the ion source. Ion beam energy correlations for operation in methane indicate that the dominant charge states on the detector are H+, C+4 and C+5. The correlation of ion beam intensity with filling gas pressure indicates that the beam emission maximizes at the optimum pressure for focus formation at peak current. Estimated ion fluxes are maximum for the energy range of 50 – 100 keV, 100 – 200 keV and 300 – 400 keV, respectively. Measurements of the angular distribution of ions reveal a strong anisotropy. It is observed that the flux of hydrogen ions is maximum near the axis of the PF whereas the flux of carbon ions is maximum at off axis (around 15°). An ion emission dip is observed in case of the carbon ions at the PF axis.