INVESTIGATIONS ON THE TRANSITION BETWEEN COLUMN AND MICROPINCH MODE OF PLASMA-FOCUS OPERATION

X-ray emission from pinch plasma devices with pinch currents ranging from 200 to 400 kA operated with pure high-Z gases are investigated with temporal spatial and spectral resolution. If operated using elements Z<18 (e.g., nitrogen or neon) K-shell emission is observed from column-like volumes several 100 mu m in diameter and several mm in length (bulk or column mode). For Z>18 (e.g., krypton or xenon) emission with h nu>1 keV is only observed from micropinches. For argon (Z=18) both modes of operation can be observed. The occurrence of a specific mode depends on the initial gas pressure. In this paper the transition regime between column and micropinches is investigated with particular regard to argon. A criterion is proposed to decide whether column mode or micropinch mode is expected. (C) 1995 American Institute of Physics.