On filamentation in the dense plasma focus

TL;DR

This paper discusses recent observations and a new model of filamentation in plasma focus devices, suggesting that filamentation is an inherent feature linked to traveling current distributions behind shock waves.

Contribution

It introduces a novel interferometry technique enabling filament observation in pure deuterium plasma focus, and proposes a feasible computational model for filamentation as a native plasma focus feature.

Findings

Filaments observed in pure deuterium PF-1000 using new interferometry.

Filamentation linked to traveling current behind shock waves.

Proposed model treats filamentation as an inherent plasma feature.

Abstract

Striking pictures showing filamentary structures in plasma focus have intrigued researchers from the early days of plasma focus research. A definitive understanding of their occurrence, origin, structure and role in plasma focus physics is still not in sight as summarized in a recent comprehensive review. This is because they are often not observed in a "standard mode" of plasma focus operation with pure deuterium, particularly in large installations, but are found in smaller experiments or those with gaseous admixtures. This has led to the suspicion that filaments are not a native feature of the plasma focus phenomenon. Recent success in observation of filaments in PF-1000 in a pure deuterium operation by a novel modification of the interferometer system that allows simultaneous interferometry and schlieren photography changes this situation. This Letter looks at the implications of this development in the larger context of plasma focus physics. Conceptualization of filamentation as a native feature of the traveling current distribution behind an ionizing strong shock wave is shown to be a feasible paradigm that can be formulated as a computable model for filamentation in the plasma focus.