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

Abstract

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.

Breakthrough in 4π ion emission mechanism understanding in plasma focus devices

“…Such studies usually report the position of maxima or minima on the X or Y axes profiles22232425262728293031. As an example of 2D ion angular distribution profiles, Fig.…”

“…As a result, for all plasma-material interaction studies by means of different scale PFDs from PF-1000141819 to miniature PFDs20, the specimens are usually placed along the z-axis of the PFD chamber to be exposed to ions by applying several pinch shots21. Many exclusive studies have been performed on ion emission angular distribution profiles on X or Y axes of PFDs; some studies have reported maxima22232425 and some have shown minima262728293031, on the profiles, on or around the z-axis. Some theoretical models have also been developed to justify ion angular distribution profiles around the z axis222324293032333435.…”

“…However, most experimental studies on ion fluence and energy measurements made so far are by using one or a short array of single small detectors on the z-axis or within a small solid angle on or around it or on X or Y axes by applying several pinch shots. The detectors usually used in such studies include activation detectors741, magnetic analyzers42, Faraday cups (FC)252843, Thomson spectrometer44 and in particular polymer track detectors like CR-39 (polyallyl-diglycol-carbonate film), PM-355 (super-grade polyallyl-diglycol-carbonate film), CN (cellulose nitrate film) and LR-115 (red-dyed cellulose nitrate film). These polymer detectors can register tracks of ions such as protons, deuterons, alpha particles or heavier ions usually by a chemical etching process followed by microscopic observation and counting716182745.…”

Temporal and spatial study of neon ion emission from a plasma focus device

“…As a matter of fact, this type of pressure dependence of the ion beam flux is a commonly observed phenomenon in PF device. 35,36 While operating the PF device in nitrogen medium Mohanty et al 36 found more ion flux in between the pressure range of 0.3-0.5 Torr. The ion beam flux, in our case, is found to be more approximately at 0.3 Torr pressure as evident from Fig.…”

“…The emission of the polyenergetic ions is a general characteristic of the PF device. [35][36][37] However, the lowest and the highest energy ions may differ from the experiment to experiment and the detection methodology. Bostick et al observed the deuteron energy spectrum ranging from 300 keV to 9 MeV, 38 whereas Gardin et al measured the deuteron energy down to around 25 keV.…”