The effect of pre-ionization by a shunt resistor on the reproducibility of plasma focus x-ray emission

The effect of pre-ionization by means of a shunt resistor on the x-ray emission of a low energy (1.8 kJ) plasma focus device powered by a 9 mu F capacitor bank, charged at 20 kV and giving a peak discharge current of about 175 kA is investigated. Quantrad Si pin-diodes along with a suitable filter are employed as time-resolved x-ray detectors, whereas a multipinhole camera with absorption filters is used for time-integrated analysis. X-ray flux in 4 pi-geometry is measured as a function of argon filling pressure with and without pre-ionization. It is found that appropriate selection of the shunt resistor increases shot-to-shot reproducibility of the x-ray emission as well as the stability of the pinch filament and broadens the x-ray pulse width. The x-ray emission is also enhanced by ( 45 +/- 5)% at the optimum pressure.