A multiple Faraday cup assembly has been developed for measuring pulsed ion beam of a low energy plasma focus device. The Faraday cups operating in biased ion collector mode have nanosecond response and these have been used to determine the energy spectrum and flux of fast nitrogen ion beam emerging out of the pinched plasma column. The design feature that makes our Faraday cups unique is that they can register ion energy of higher kinetic value (∼hundreds of keV) as well as lower kinetic value (∼keV). It has been possible to register the ion energy upto a lower kinetic energy threshold of ∼5 keV which is a value much lower than that obtained in any previous works. The correlation of the ion beam flux with filling gas pressure is also reported. Angular distribution of ion measurement reveals a highly anisotropic emission indicating an ion dip at the electrode axis.

An investigation on the soft x rays emitted in a 2.2 kJ Mather-type dense plasma focus device using a multichannel diode spectrometer and a simple pinhole camera is reported. Emitted x rays associated with different shapes (hollow, solid, and hemispherical) of anode and in hydrogen/nitrogen gas medium are compared. The structure of x-ray emitting sites as well as x-ray yields were found to be strongly influenced by the shape of the anode and the filling gas pressure. The maximum yield of 2.2 J into 4π sr was obtained in the case of hemispherical anode in hydrogen gas medium. The x-ray pinhole images of the collapsed plasma with the hemispherical anode indicated spot-like structure having 500–800 μm in diameter. On the contrary, other anode shapes showed columnar pinched structure of 8–10 mm in length and 1–2 mm in diameter. Results indicated that an appropriate design of the anode could enhance the x-ray yield by more than tenfold in a conventional low energy dense plasma focus device.

The development of a novel and portable tabletop pulsed neutron source is presented. It is a battery powered neutron tube based on a miniature plasma focus (PF) device having all metal-sealed components. The tube, fuelled with deuterium gas, generates neutrons because of D–D fusion reactions. The inner diameter and the length of the tube are 3.4 cm and 8 cm, respectively. A single capacitor (200 J, 4.0 µF, 10 nH) of compact size (17 cm × 15 cm × 13 cm, 6.5 kg) is used as the energy driver. A power supply system charges the capacitor to 10 kV in 10 s and also provides a 30 kV trigger pulse to the spark gap. An input of 24 V dc (7.5 A) to the power supply system is provided by two rechargeable batteries (each 12 V, 7.5 A, 20 h). The device has produced neutrons for 150 shots within a period of 120 days in a very reliable manner without purging the deuterium gas between the shots. For the first 50 shots, the average yield is (1.6 ± 0.3) × 106 neutrons/shot in 4π sr with a pulse width of 23.4 ± 3.3 ns. The estimated neutron energy is 2.47 ± 0.22 MeV. The neutron production reduces slowly and reaches the detection threshold value of 3 × 105 neutrons/shot towards the last shots. The device produces neutrons in a similar manner on evacuation and refilling. The height of the mounted PF tube with the capacitor and the spark gap is 35 cm. The complete setup comprising the capacitor with spark gap, the PF tube, the power supply system with two batteries and the control panel weighs only 23 kg.

A comparative study on the ion emission characteristics such as flux and energy, and their variation in angular positions and operating gas pressures has been carried out in a nitrogen-filling plasma focus device. Three different designs of cylindrical anode (central electrode) having hollow, solid and hemispherical tip have been tested for this study. The ion emission characteristics were investigated by employing three Faraday cups at various angular positions. The ion flux depends on the operating gas pressure irrespective of the anode designs and the maximum ion flux is found to be in the pressure range 0.3 to 0.5 Torr for all the anode designs. The hemispherical anode yields highest ion flux while the hollow anode emits lowest ion flux. The angular variation of ion flux is seen to be anisotropic irrespective of the anode designs with an ion dip at 0 (axis of the device) and maximal at 5 angular positions. The anisotropic character of ion emission is less in the case of the hemispherical anode than the hollow anode. The ion energy, measured by the time of flight method, shows its dependence on the anode designs. The maximum ion energy is found to be around 830 keV at an angular position 5 in the case of the hemispherical anode design. The most probable ions are found to be with energy less than 100 keV irrespective of the anode designs and the angular positions. This study indicates that the plasma focus device could be optimized to a great extent for optimal ions yield by using an appropriate anode design.

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