Historical research guide · 1054 · 2002
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
In one minute
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.
Connection
Chapter 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.
From the source
A 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
The 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
The 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
A 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
The 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
What 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
The way in
https://doi.org/10.1063/1.1487898How 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