Ion jet produced by anomalous resistance in plasma focus discharge

Abstract

The dense plasma focus (DPF) device belongs to the category of noncylindrical Z-pinch facility that produced pinched plasma of very high temperature and high density by electromagnetic acceleration and compression. The plasma pinch produced in few mbar of gas filling exhibited a large range of complex physical phenomena which is also an abundant source of multiple pulsed radiations such as neutrons, ion beam and electron beam, soft and hard X-ray. In this work, ion beam is generated by a 3.3 kJ Mather type plasma focus operated in less than 1 mbar of deuterium filling. The electrode geometry of the plasma focus tube has been optimized to allow the matching of the electrical characteristic time and current sheath dynamic time. Reproducible pinch is observed in low pressure discharge where the current drops for about 26% from the peak value during pinch and last for more than 350 ns. This indicates a large portion of energy has been drawn by the pinch action. This phenomenon is less significant in normal plasma focus discharge operated at higher operation pressures. The ion beam energy measured is found correlated closely to the magnitude of current drop. The instabilities onset during the pinch resulting anomalous resistance that accelerates ions and electrons beams to intense high energy. This effect was found to be enhanced in lower pressure operation with prolong current drop. At discharge voltage of 15 kV, average ion beam of 20–50 keV were measured. The ion beam was determined by using two biased ion collectors for time-offlight measurement, solid state nuclear track detectors for angular distribution measurement. These results confirmed the presence of a large accelerating electric field that could be due to the intensified instabilities at low pressure regime.