Current sheath dynamics and X-ray emission studies from sequential dense plasma focus device

Abstract

A conventional dense plasma focus (DPF) device shows one or two compression phases. In the present paper, we report on a sequential DPF device with modified central electrode design to obtain more than two compression phases (i.e., multiple focusing). The sequential focusing was optimized by taking six different electrode designs for different filling gas pressures of argon. The optimization was inferred on the basis of intensity of spikes of voltage probe signals. The optimized central electrode design has then been used to study current sheath dynamics and X-ray emission using nitrogen laser shadowgraphy and diode X-ray spectrometer, respectively. Shadowgraphs show the breaking of current sheath during first focus as one part of it goes into radial collapse phase, and the other remains in axial acceleration phase. The one that remains in axial phase moves axially ahead in comparison to the other part of the current sheath. A bubble formation is observed after first focus phase. Shadowgraphs also show the formation of weak off-axis second focus. Finally, an on-axis third radial collapse is observed shadowgraphically (X-ray signals depict a multispike structure indicating hereby a sequential X-ray bursts from the sequential DPF device). The plasma electron temperatures have also been estimated using these X-ray signals.