Design and construction of a very low energy plasma focus, operating at repetitive discharge mode and pinching evidences

As a first step toward the demonstration of pinching evidence using a very low energy discharge, we have designed and constructed a very small plasma focus device of 3J (PFD-3J) as a repetitive pulsed and portable radiations source. The system is capable of operating in a repetitive discharge rate up to 5 Hz as well as very low energy consumption (84 nF capacitor bank, 48 nH, 8-9 kV, ∼2.5-3.5 J). Several diagnostic tools, a CMOS digital single-lens reflex camera, current and voltage probe, are employed simultaneously to confirm the occurrence of pinching in the device. When the system is operated in discharges at 0.9 torr argon gas pressure and initial charging voltage of 8.4 kV, the focusing/pinching indications are genuinely observed as the appearance of a sharp voltage spike/intense current drop on the electrical discharge traces. The PFD-3J performance at repetitive discharge mode was also verified by adjusting the high voltage pulsed-power supply (HVPPS) at 5 Hz shot frequency. It was observed that the rise time of 10%-90% of the charging voltage, at each single shot trace was 115 ms as expected from the design.