Historical research guide · 0384 · 2011
Dynamics and Density Measurements in a Small Plasma Focus of Tens-of-Joules-Emitting Neutrons
Ariel Tarifeño-Saldivia · Cristian Pavez · José Moreno · Leopoldo Soto
In one minute
A plasma focus fires a capacitor bank into two coaxial electrodes; the current sheet sweeps down the barrel, folds over the end and collapses onto the axis, squeezing a tiny knot of plasma dense and hot enough to fuse deuterium. Ariel Tarifeño-Saldivia, Cristian Pavez, José Moreno and Leopoldo Soto ran that experiment on PF-50J, a machine storing only tens of joules and driving only tens of kiloamperes, and looked inside it with interferometry — reading how much the plasma bends a laser beam to recover the electron density and the shape of the collapse, shot by shot. They tracked the radial phase, measured the conditions in the pinch itself, and recorded the neutrons from the same shots. The finding is the one that matters for anyone who wants fusion-relevant plasma on a bench: the dynamics, the pinch conditions and the electron densities that large plasma-focus machines produce are all present in a device operating at tens of joules.
Connection
Chapter 12 needs evidence that the plasma conditions for fusion do not require a hall-sized machine, and this is the direct density measurement that says so; chapter 9 studies self-organising, self-compressing plasma structures, and the pinch is the cleanest laboratory example of one.
From the source
Interferometry was used to study the dynamics of the radial phase and the plasma conditions in the pinch phase of PF-50J, a plasma focus operating in the range of tens of joules stored in the capacitor bank and tens of kiloamperes of current.Abstract, sentence 1; IEEE Transactions on Plasma Science 39, 756 (2011)
The experiments used deuterium as the filling gas, and neutron production was measured simultaneously with the interferometry, so the plasma conditions and the fusion signal come from the same shots rather than from separate campaigns.Abstract, sentence 2; title
The result is that the typical dynamics, the pinch conditions and the electron density observed in much larger machines are also present in a device operated at only tens of joules.Abstract, final sentence
This raises the standard of evidence for the small plasma focus: the same group’s earlier work established the pinch at tens of joules from electrical signatures alone, while here the density and the collapse are measured directly by an optical method and are accompanied by neutrons.Title and abstract, read against Silva, Soto, Kies and Moreno, Plasma Sources Science and Technology 13, 329 (2004)
What to watch: the scaling question this line of work opens is how neutron yield per joule behaves as the device shrinks further, and whether the emission in these very small devices is dominated by beam-target or thermonuclear processes — the measurement is a yield-and-spectrum campaign across the group’s progressively smaller machines.Abstract, final sentence; the device series described in the same authors’ subsequent work
The way in
https://doi.org/10.1109/tps.2010.2091111How to cite it
Ariel Tarifeño-Saldivia, Cristian Pavez, José Moreno, Leopoldo Soto (2011) Dynamics and Density Measurements in a Small Plasma Focus of Tens-of-Joules-Emitting Neutrons doi:10.1109/tps.2010.2091111