Search

This paper reports the results of characterization and optimization experiments carried out on a newly developed NX-3 dense plasma focus device (20 kJ at 20 kV, a quarter time period of \sim\!\!3\ \mu\s, and 10 kJ/600 kA at 14 kV) at the Plasma Radiation Source Laboratory, NIE, Nanyang Technological University, Singapore. Initial experiments were conducted with an electrode assembly configuration having anode radius and length of 20 and 160 mm, respectively, for detailed neutron emission characterization of NX-3 device followed by further optimization of neutron yield using various other electrode configurations designed using the Lee Code. At \geq10-kJ operation, the average neutron yield on the order of 10^9 neutrons/pulse in 4\pi\sr was obtained for the deuterium filling gas pressure range of 6–8 mbar. The neutron yield of \sim\!\!4.6 \times 10^9 neutrons/pulse at 10 kJ/6 mbar is the highest ever reported for a device with the same stored energy. The neutron anisotropy measurements point to the beam–target mechanism as the dominant neutron production mechanism for NX-3 plasma focus device. Further optimization of neutron yield in NX-3 was achieved with the peak average neutron yield being enhanced from \sim\!\!(2.38 \pm 0.31) \times 10^9 neutrons/shot for the initial electrode configuration to about \sim\!\!(3.40 \pm 0.43) \times 10^9 neutrons/shot for the electrode configuration with anode radius and length of 26 and 140 mm, respectively. The analysis of neutron yield results for various electrode assembly configurations demonstrates the speed factor as a key optimization tool for maximization of neutron yield. [ABSTRACT FROM PUBLISHER]

A table top ~0.2-kJ miniature plasma focus (PF) device "FMPF-1" (2.4 µF, 27 ± 2 nH, T/4 ~400 ns, 9-14 kV) has been successfully used as a compact and portable, pulsed hard X-ray (HXR) source for fast (< 32-ns exposure time) radiography applications using Hydrogen (H2) as filling gas. The overall dimensions of the apparatus, which includes capacitor bank, sparkgap switch, and the focus chamber, are 0.2 m x 0.2 m x 0.5 m, and the system weighs about 25 kg. The time resolved information of HXR emission and their relative yield along the axial (0°) and radial (90°) directions are measured using a pair of cross-calibrated scintillator-photomultiplier detectors. The average pulse durations (full-width at half-maximum) of HXR pulse are measured to be 29±3 ns in axial direction and 18±2 ns in the radial direction. The average axial to radial HXR yield anisotropy is found to be 3.9 ± 0.9 at the optimum pressure of 3.5 mbar. The experimental estimation of the effective average energy of the HXR emission, with high-Z (Pb) insert in stainless steel anode is found to be in the range of 60-80 keV. The potential of the miniature PF as compact radiographic source is illustrated by radiographic imaging, with submillimeter range (< 0.3 mm) spatial resolution, of different objects placed outside the chamber. [ABSTRACT FROM AUTHOR]