STM-D-0572Paper2017Published and peer-reviewed

The Plasma Focus—Numerical Experiments, Insights and Applications

S. Lee · S. H. Saw

Summary and citation · read the original at the source

In one page

A plasma focus is a capacitor bank fired into a pair of coaxial electrodes: the current sheet sweeps down the tube, collapses onto the axis, and for a few billionths of a second makes a pinch hot and dense enough to fuse deuterium. Sing Lee and Sor Heoh Saw wrote the simulation code most plasma focus laboratories run, and this long chapter is their account of what thirty years of numerical experiments with it have taught. They set out the physics and the equations, and explain why so simple a model tracks so much real behaviour: the electromagnetic drive, the copious radiation, the fusion neutrons, the fast ion beams, the anomalous resistivity of plasma instabilities, and the states of extreme high energy density reached by radiative collapse. The trick is four parameters fitted to a measured current waveform: a mass swept-up factor and an effective current factor for the axial phase, and two more for the radial phase. Once matched, every mechanism is accounted for in the mass and energy balance, including ones nobody has yet recognised.

Why it matters hereChapter 9 is about self-organised plasma structures and the focus pinch is the most heavily measured one in any laboratory; chapter 12 needs fusion in a compact repeatable machine rather than a reactor hall. This chapter is the field’s working manual for both — the code, its equations, and the scaling laws that tell you what a given machine will do before anyone builds it.

What it claims

01The plasma focus exhibits phenomena ranging from electromagnetically driven dynamics to copious radiation — ions, electrons, X-rays and characteristic soft X-rays, fusion neutrons, fast ion beams and fast plasma streams — to anomalous resistivity from a range of plasma instabilities, to plasma states of extreme high energy density achieved through radiative cooling and collapse, and the Lee Model code succeeds in modelling many of these many-sided aspects.Abstract
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02The code’s success on so many fronts is attributed to its use of four parameters, fitted to a measured current waveform, which in one sweep incorporate all the mechanisms and effects occurring in the plasma focus, including mechanisms difficult to compute or as yet unrecognised.Abstract
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03The premise is that the sum total of those mechanisms is represented, in the gross sense, by mass field and force field distributions: a mass swept-up factor and an effective current factor in the axial phase, and two corresponding factors in the radial phase, carried up to the end of the focus pinch.Abstract
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04Once the computed current waveform is matched to the measured one, the fitted model parameters assure that the computation proceeds with all physical mechanisms accounted for, at least in the gross energy and mass balance sense.Abstract
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05The chapter gathers thirty years of numerical experiments with this one code and sets them against the wider simulation literature on the plasma focus — the review the field had not previously had in one place.Abstract; Chapter 3, pages 113 to 232
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06The open question the code puts on the bench is how far a plasma focus can be pushed: the authors’ companion work identifies the current sheet’s own dynamic resistance, about seven milliohms in deuterium, as the ceiling on neutron yield, and proposes raising the operating voltage rather than the stored energy as the way past it.Chapter 3, pages 113 to 232; set out in full in the authors’ open-access 2010 paper, Section 6
What to watch

The way in

https://doi.org/10.1007/978-981-10-4217-1_3Chapter 3 of ’Plasma Science and Technology for Emerging Economies’, pages 113 to 232, first online 8 October 2017, under Springer’s subscription terms with no Creative Commons statement. The chapter itself could not be read for this sheet; the summary and the first four claims are written from the publisher’s abstract, quoted verbatim on the Springer landing page, and from the Crossref record. The authors’ own open-access account of the same code — same programme, same four fitted parameters — is in this library at /library/stm-fbd01b5713 and was read in full.

How to cite it

S. Lee, S. H. Saw (2017) The Plasma Focus—Numerical Experiments, Insights and Applications. doi:10.1007/978-981-10-4217-1_3

Where it sits in the curriculum

Plasmoids, charge clusters and the orbs Lattice confinement fusion