Observations of radial wild cables in z-pinch plasma (abstract)

Abstract

The results of processing the z-pinch plasma images with the help of the method of multilevel dynamical contrasting (MDC)1(a),1(b) are presented. This method was earlier used for: (i) analyzing the filaments (and their networks) in a gaseous z-pinch1(a),1(c) and (ii) characterization of long-living filaments2 of the lifetime comparable with the entire duration of discharge. The original images were taken in visible light, with space resolution ∼100 μm and time resolution ∼2–60 ns. The long-life structures are found, which are assembled from straight cylindrical blocks varying in length from a few millimeters to a few centimeters. Such blocks are of various orientation in space, and often they form a common frame. The most important phenomenon is the presence of radial (with respect to z-pinch axis) filaments directed from the periphery to the core, up to the z-pinch axis. An analysis of the fine structure of the above cylindrical blocks of few millimeter diameter reveals them to be a coaxial structure with the diameter of an inner rod (which may be of tubular form) approximately smaller by an order of magnitude. A comparison is made with similar structures recently observed in tokamak plasmas.3(a) The reliability of the above results is supported by the rich statistics and considerable similarity of the structuring in various regimes, and insensitivity to specific way of imaging. Sometimes the structuring may be seen without MDC processing (in such cases, the MDC allow fine resolution of structuring). The experimental results are analyzed from the viewpoint of the hypothesis3 about “wild cables” in plasmas of high-current electric discharges. The correlation is found between the measured values of the high-frequency electric fields in z-pinch plasma and the values of the Miller force needed to sustain vacuum channels in the plasma which are the essential elements of the wild cable