STM-D-0612Paper2004Published and peer-reviewed

Implosion dynamics of wire array Z-pinches: experiments at Imperial College

S. V. Lebedev · D. J. Ampleford · S. N. Bland · S. C. Bott · J. P. Chittenden · C. Jennings · M. G. Haines · J. B. A. Palmer · J. Rapley

Summary and citation · read the original at the source

In one page

A Z-pinch is the simplest fusion machine there is: run a colossal current down a column of matter and its own magnetic field crushes it inward. At Imperial College the column is a cage of fine wires, and Lebedev and his colleagues report what the MAGPIE generator — about a million amps in a quarter of a microsecond — actually shows happening inside one. The wires do not simply collapse like a falling shell. Each wire stays put as a solid core wrapped in plasma, and that plasma streams inward ahead of everything else, quietly redistributing the array’s mass before the implosion proper begins. How fast a wire gives up its plasma depends on the collective magnetic field of the whole array and rises with it. Because the streaming is uneven along each wire’s length, the imploding sheath leaves material behind it, and that trailing mass carries some of the current on a path of its own — which is exactly the force the pinch loses when it finally stagnates.

Why it matters hereChapter 9 is about plasma that organises its own structure, and a wire array is the cleanest laboratory case there is: the cores, the coronas and the inward streams arrange themselves, and the machine’s output is decided by that self-organisation rather than by the drive alone. Chapter 12 gets the practical lesson — the current that leaks into trailing mass is the compression a fusion pinch does not get, which is why array geometry, not just stored energy, sets what these machines can do.

What it claims

01The implosion of a wire array is not a simple snowplough. A gradual redistribution of the array mass by the precursor plasma flow from the wire cores plays a very important role in the implosion dynamics — the wires form a core and corona structure, and plasma streams inward from stationary cores well before the sheath itself moves.Abstract
Published and peer-reviewed
02The rate of wire ablation depends on the magnitude of the global, collective magnetic field of the array, and increases as that field increases — so the array as a whole, not each wire on its own, sets how quickly mass is delivered to the axis.Abstract
Published and peer-reviewed
03The ablation rate is modulated along the length of each wire, and that modulation leaves a trailing mass behind the imploding current sheath rather than carrying all of the array material inward with it.Abstract
Published and peer-reviewed
04The trailing mass provides an alternative path for the current, and that shunted current reduces the force available for compression of the pinch at stagnation — the loss is in the current distribution, not in the drive.Abstract
Published and peer-reviewed
05The experiments are performed on the MAGPIE generator at Imperial College London, which delivers of order one mega-amp in about 250 nanoseconds, and the programme exists to feed measured implosion physics into the design of the much larger pulsed-power machines used for radiation and fusion work.Abstract; title and affiliation
On the bench now
06The open question the paper hands forward is how much of the lost compression can be recovered by engineering the array — wire number, wire material and array geometry — so that ablation is uniform along the wires and little or no trailing mass is left for the current to find.Abstract, closing statement on stagnation
What to watch

The way in

https://doi.org/10.1088/0029-5515/44/12/s12LICENCE AND TEXT. Published as Nuclear Fusion volume 44, number 12, pages S215 to S220, December 2004. The Crossref record carries no licence of any kind, OpenAlex and Unpaywall both report the work closed with no repository copy anywhere, and the publisher’s servers answer automated requests with a bot-manager challenge rather than the article, so this page carries no reproduced text and no quoted abstract. The summary and the claims are the site’s own, written from the bibliographic record and from the publisher’s abstract as it is indexed by the search services, and every locator below therefore names the abstract rather than a section of the full text. REGISTRY CORRECTION. The record reached the library with eight of the nine authors; the ninth, J. Rapley, is restored here from the publisher’s own by-line. THE MACHINE. The experiments are on MAGPIE, the Mega Ampere Generator for Plasma Implosion Experiments in the Plasma Physics Group at Imperial College London, which drives about one mega-amp in about 250 nanoseconds. TWO SIBLING RECORDS. Two closely related Lebedev-group papers are already in this library as unfilled skeletons — the 2001 Physics of Plasmas paper on discrete-wire effects and the 2004 paper on equilibrium flow structures and implosion trajectories — and are not linked below because they carry no summary yet.

How to cite it

S. V. Lebedev, D. J. Ampleford, S. N. Bland, S. C. Bott, J. P. Chittenden, C. Jennings, M. G. Haines, J. B. A. Palmer, J. Rapley (2004) Implosion dynamics of wire array Z-pinches: experiments at Imperial College. doi:10.1088/0029-5515/44/12/s12

Where it sits in the curriculum

Plasmoids, charge clusters and the orbs Lattice confinement fusion