Investigations on the transition between colomn and micropinch mode of plasma focus operation

In plasma focus devices operated with pure nitrogen, neon or argon (Z equal or smaller than 18) with pinch current from 200 to 400 kA the emitting region is a column with several 100 mym in diameter and several mm in length (column mode). For Z equal or bigger than 18 micropinches are observed. Usually micropinches and column emission is examined independently. Small Plasma Foci feature both modes simultaneously. In this paper the transition regime between column and micropinches is investigated with particular regard to Z = 18 (argon). Peculiarities in the emitted spectra are interpreted by the interaction of simultaneous existing column and micropinch plasma.