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

X-ray emission from pinch plasma devices with pinch currents ranging f rom 200 to 400 kA operated with pure high-Z gases are investigated wit h temporal spatial and spectral resolution. If operated using elements Z<18 (e.g., nitrogen or neon) K-shell emission is observed from colum n-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 m odes of operation can be observed. The occurrence of a specific mode d epends on the initial gas pressure. In this paper the transition regim e between column and micropinches is investigated with particular rega rd to argon. A criterion is proposed to decide whether column mode or micropinch mode is expected. (C) 1995 American Institute of Physics.