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.

https://iopscience.iop.org/article/10.1143/JJAP.44.5199/pdf

Development of Multi Faraday Cup Assembly for Ion Beam Measurements from a Low Energy Plasma Focus Device

The room temperature nitriding of titanium is accomplished by utilizing nitrogen ion beams delivered by a 2.3 kJ plasma focus discharge. Titanium samples are exposed to ions at different axial positions (3, 5, 7 and 9 cm from the focus) in order to correlate their surface properties with ion beam parameters such as energy, number density, current density and energy flux (energy deliverance per unit time per unit volume). A BPX65 photodiode detector is employed to measure the ion beam parameters by using the time of flight technique. X-ray diffraction analysis as well as field emission scanning electron microscopy along with the energy dispersive x-ray spectroscopy is carried out to explore the structural, morphological and compositional profiles of the treated samples. The results demonstrate the formation of nanocrystalline TiN thin film with surface features strongly dependent on ion beam energy flux. A Vickers microindentation measurement reveals that the surface hardness is improved 4–5 times for typical nitrided samples. (Some figures in this article are in colour only in the electronic version)

Nitriding of titanium by using an ion beam delivered by a plasma focus

The effect of three different anode shapes, flat, tapered and hemispherical, on the x-ray emission characteristics of a neon filled UNU–ICTP plasma focus device is investigated. The current sheath dynamics, in the radial collapse phase, has been simultaneously interrogated using the laser shadowgraphy method to understand the variation in x-ray emission characteristics for anodes of different shapes used in the experiments. The maximum neon soft x-ray (SXR) yield for the flat anode is about 7.5 ± 0.4 J at 4 mbar, whereas for hemispherical and tapered anodes the neon SXR is almost halved with the optimum pressure shifting to a lower value of 3 mbar. The laser shadowgraphic images confirm that the reduction in the overall neon SXR yield is due to the reduced focused plasma column length for these anodes. The relative HXR yield was the highest for the hemispherical anode followed by the tapered and the flat anodes in that order. The shadowgraphic images and the voltage probe signals confirmed that for the hemispherical anode the multiple-pinch phenomenon was most commonly observed, which could be responsible for multiple HXR bursts for this anode with maximum HXR yields.

https://iopscience.iop.org/article/10.1088/0022-3727/42/4/045203/pdf

The effect of anode shape on neon soft x-ray emissions and current sheath configuration in plasma focus device

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.

Effect of Anode Designs on Ion Emission Characteristics of a Plasma Focus Device

Study on electron beam emission from a low energy plasma focus device

This paper reports on the modification of a small plasma focus device (UNU/ICTP PFF) to operate at low pressure for enhanced ion beam generation. For the present operation, the electrode geometry of the plasma focus device is modified to redirect the plasma motion at the end of the axial rundown phase so that normal plasma focus action will not occur. The redirection of the plasma leads to a rapid increase in the plasma resistivity and hence a high localized electric field will be established and as a result, high energy ion beam will be generated. With air as the working gas, pressure as low as 10-3 mbar has been tested. At such a low pressure, breakdown of the discharge must be initiated with the use of a set of twelve plasma injection cable guns. The modified plasma focus has been shown to be able to produce high energy ion beams of nitrogen, argon and hydrogen consistently.

http://iopscience.iop.org/article/10.1143/JJAP.41.3943/pdf

Generation Of High Energy Ion Beams from a Plasma Focus Modified for Low Pressure Operation

Pulsed capillary discharge is a compact device that is used to perform fast electrical discharge that is used to produce transient plasma. In this work, a more economical imaging technique is developed in order to study the dynamics of the plasma that is formed in a capillary tube. The imaging system consists of two main devices, a four‐frame gated micro‐channel plate and a Nikon Coolpix5000 camera. The time‐resolved imaging that we have performed in order to study the dynamics of the plasma that is formed in a 10 mm long and 1 mm diameter low pressure capillary tube is reported. The images obtained portrayed that the plasma is heated up when the magnitude of the current is around the maximum and cools down when the current magnitude is around the minimum.

Jasbir Singh

Papers

Generation Of High Energy Ion Beams from a Plasma Focus Modified for Low Pressure Operation

Time‐Resolved Imaging Of Transient Plasma