Historical research guide · 1006 · 2004
Plasma dynamics during the evolution of two wire Z-pinch
F. N. Beg · J. Ruiz-Camacho · M. G. Haines · A. E. Dangor
In one minute
A Z-pinch is a wire vaporised by an enormous current pulse, with the current’s own magnetic field crushing the resulting plasma inward. The big machines use arrays of hundreds of wires, and how neighbouring wires affect each other decides how the implosion goes. Beg, Ruiz-Camacho, Haines and Dangor at Imperial College strip that question to its smallest version: two parallel wires, a peak current of 160,000 amps delivered in about 65 billionths of a second, aluminium or tungsten, at three different spacings. What they report is that two wires do not simply become two plasmas. A third plasma column appears in the gap between them, well before the wires themselves implode, and the vapour boiling off each wire expands lopsidedly rather than in a neat cylinder. All three plasmas go unstable, in different ways: the wires develop sausage-like necking, in step with one another, while the central column kinks sideways in the plane that contains both wires. That middle instability tells the authors current has moved off the wires into the plasma they made.
Connection
Chapter 9 follows plasma that organises itself into structures that hold together and carry current, and this is the smallest clean laboratory case of it: two current-carrying filaments spontaneously build a third column between them and hand it part of their current. It is also the physics that governs every wire-array driver used for pinch fusion, so it sits directly upstream of the machines chapter 12 depends on.
From the source
Two parallel wires driven together do not stay two plasmas. Besides the plasma at each wire and its surrounding corona, a distinct plasma column forms centred in the gap between the wires, and it forms well before the wires themselves implode.Abstract
The corona around each wire expands asymmetrically rather than in a cylindrically symmetric shell, so the presence of the neighbouring wire shapes the ablation flow from the start.Abstract
All three plasmas become unstable, and the mode depends on which plasma it is: the wire plasmas show the characteristic m equals zero sausage perturbation, while the central column shows predominantly the m equals one kink.Abstract
The instabilities are organised by the geometry rather than random: the m equals zero perturbations on the two wires are spatially correlated with each other, and the m equals one perturbations of the central plasma develop in the plane that contains the two wires.Abstract
The growth of instability in the central column implies that some of the current has transferred from the wires into that column, so the plasma the wires create takes over part of the drive current before implosion.Abstract
The experiment is run at a scale where the geometry can be varied deliberately: a pulsed-power source of 160 kiloamps peak with a 65 nanosecond rise time from 10 to 90 percent, aluminium wires of 15 micrometres and tungsten wires of 7.5 micrometres, at wire separations of 0.3, 0.6 and 1.5 millimetres.Abstract
The way in
https://doi.org/10.1088/0741-3335/46/1/001How to cite it
F. N. Beg, J. Ruiz-Camacho, M. G. Haines, A. E. Dangor (2004) Plasma dynamics during the evolution of two wire Z-pinch doi:10.1088/0741-3335/46/1/001