A plasma focus driven by a capacitor bank of tens of joules
Patricio Silva · Leopoldo Soto · José Moreno · Gustavo Sylvester · Marcelo Zambra · Luis Altamirano · Horacio Bruzzone · Alejandro Clausse · César Moreno
Abstract and summary · read the original at the source · none found
In one page
A plasma focus is a beautifully simple machine: dump a capacitor into a pair of coaxial electrodes, and the current sheet it launches sweeps down the gun, folds inward and collapses a knot of plasma dense and hot enough to fuse. The big ones fill rooms and swallow hundreds of kilojoules. Patricio Silva, Leopoldo Soto and their colleagues at the Chilean Nuclear Energy Commission built one that runs on a few tens of joules — a 160 nanofarad bank at 20 to 40 kilovolts — as the first step toward a repetitive pulsed neutron source. They photographed it with a five-nanosecond camera and saw exactly what the room-sized machines show: the umbrella-shaped current sheath rolling over the ends of the electrodes, and the pinch forming after the radial collapse. The physics did not care that the energy was smaller by orders of magnitude. Their calculations put ten thousand to a hundred thousand neutrons per shot within reach in deuterium.
Why it matters hereChapter 9 is the self-organising plasma knot, and this paper is the demonstration that the dense plasma focus keeps its structure when you shrink the drive by orders of magnitude — which is what makes a table-top plasmoid experiment possible at all. Chapter 12 is fusion at small scale, and a device that fits on a bench and still expects neutrons is the cheapest route anyone has to repeatable fusion experiments.
What it claims
01A very small plasma-focus device was designed and constructed as a first step in the design of a repetitive pulsed neutron generator — the goal is not a single shot but a source that fires again and again.Abstract, sentence 1; title
Designed, not yet built02The system operates at low energy: a 160 nanofarad capacitor bank, 65 nanohenry inductance, 20 to 40 kilovolts, and about 32 to 128 joules per shot.Abstract, sentence 2
On the bench now03The design of the electrode was assisted by a computer model of the Mather plasma focus, so the geometry of a tens-of-joules gun was arrived at by calculation rather than by trial.Abstract, sentence 3
Published and peer-reviewed04A single-frame image converter camera with a five-nanosecond exposure was used to obtain plasma images in the visible range, and in the photographs the umbrella-like current sheath running over the end of the coaxial electrodes, and the pinch after the radial collapse, can be clearly observed.Abstract, sentences 4 and 5
Published and peer-reviewed05The observations are similar to the results obtained with devices operating at energies several orders of magnitude higher — the plasma focus keeps the same dynamics as the drive energy is scaled down.Abstract, sentence 6
Published and peer-reviewed06What to watch: the calculations indicate that yields of 10⁴ to 10⁵ neutrons per shot are expected with discharges in deuterium. That is a prediction in this paper, not a measurement in it, and the measurement that settles it is a counted neutron yield from the same device running deuterium — which is the experiment the same Chilean group went on to publish at higher energies.Abstract, final sentence
What to watch
Read it · abstract
Abstract
As a first step in the design of a repetitive pulsed neutron generator, a very small plasma-focus device has been designed and constructed. The system operates at low energy (160 nF capacitor bank, 65 nH, 20–40 kV, and ∼32–128 J). The design of the electrode was assisted by a computer model of Mather plasma focus. A single-frame image converter camera (5 ns exposure) was used to obtain plasma images in the visible range. The umbrellalike current sheath running over the end of the coaxial electrodes and the pinch after the radial collapse can be clearly observed in the photographs. The observations are similar to the results obtained with devices operating at energies several orders of magnitude higher. The calculations indicate that yields of 10⁴–10⁵ neutrons per shot are expected with discharges in deuterium.
Patricio Silva, Leopoldo Soto, José Moreno, Gustavo Sylvester, Marcelo Zambra, Luis Altamirano, Horacio Bruzzone, Alejandro Clausse and César Moreno, A plasma focus driven by a capacitor bank of tens of joules, Review of Scientific Instruments 73, issue 7, 2583–2587 (2002). The published paper is at doi.org/10.1063/1.1487898.
(Abstract only — no other text of the paper is reproduced here; see the rights note above. On this site, the same group’s measured neutron emission from a 400-joule fast plasma focus is at /library/stm-7b39e3fe45; the internal dynamics and density modelling of a tens-of-joules device is at /library/stm-914ae7ba20; and their survey of transient electrical discharges in small devices, which sets out why the scaling works at all, is at /library/stm-bf5c2a25ae.)
The way in
https://doi.org/10.1063/1.1487898SOURCE NOT REACHED — this page is written from the authors’ own abstract and the bibliographic record, and says so. Published as Review of Scientific Instruments volume 73, issue 7, pages 2583 to 2587, dated July 2002, by the plasma physics group of the Comisión Chilena de Energía Nuclear in Santiago with co-authors in Argentina. A NOTE ON THE VENUE: the working note that opened this sheet recorded the journal as Physics of Plasmas volume 9; Crossref, OpenAlex and OpenAIRE all give Review of Scientific Instruments volume 73, pages 2583 to 2587, and that is what is used here. Unpaywall and OpenAlex both report the article closed with no repository full text, and OpenAIRE lists no green instance for the DOI, so nothing beyond the abstract is reproduced. THE ABSTRACT below is the version deposited by AIP with Crossref, checked word for word against the copy OpenAlex holds. ONE REPAIR was made to it and nothing else: both deposits render the neutron yield as the digit run 104 to 105 where the superscripts were lost, and it is restored here to 10⁴ to 10⁵ neutrons per shot, which is the figure the sentence carries and is consistent with the same group’s later published yields at higher energies. Every locator points to a sentence of the abstract or to the bibliographic record.
How to cite it
Patricio Silva, Leopoldo Soto, José Moreno, Gustavo Sylvester, Marcelo Zambra, Luis Altamirano, Horacio Bruzzone, Alejandro Clausse, César Moreno (2002) A plasma focus driven by a capacitor bank of tens of joules. doi:10.1063/1.1487898
Where it sits in the curriculum
Fusion machines: pinches, focus devices and inertial drivers