Historical research guide · 0922 · 2006
The heating of plasma focus electrodes
E. Angeli · M. Frignani · S. Mannucci · F. Rocchi · M. Sumini · A. Tartari
In one minute
A plasma focus is a beautifully simple machine: dump a capacitor bank into two coaxial electrodes, and the current sheet that sweeps down the barrel collapses onto the axis and pinches a knot of plasma hot enough to fuse deuterium. Firing it once is easy. Firing it many times a second — which is what any practical neutron source or fusion device would have to do — runs into a plainer problem, and this paper measures it. Angeli, Frignani, Mannucci, Rocchi, Sumini and Tartari, working between the universities of Ferrara and Bologna, watched the inner electrode of a Mather-type machine cool after shots at several different bank energies, compared the decay curves against theoretical and numerical models, and extracted two candidate scaling laws linking the heat deposited to the energy stored. Their headline number is the one a designer needs: roughly a tenth of the total energy in the bank ends up in the inner electrode. They close by asking what temperature the electrode materials can actually stand.
Connection
Chapter 9’s plasma focus is the cheapest laboratory route to a dense, self-organising, fusion-relevant plasma, and chapter 12 cares whether such a machine can run continuously rather than once. This paper supplies the engineering constraint that decides it: how much of every shot lands as heat on the hardware, and how hot the hardware is allowed to get.
From the source
Plasma focus technology development today is strictly related to the possibility of a high-frequency repetitive working regime, and one of the more relevant obstacles to that goal is the heating of structural components by their direct interaction with the plasma.Abstract, sentences 1 and 2; Plasma Sources Science and Technology 15, 91 (2006)
The measurement reported is the temperature decay of the inner electrode of a Mather-type plasma focus, taken over several series of shots at different capacitor-bank energies.Abstract, sentences 3 and 4
The experimental data are analysed against theoretical and numerical models of the heating, so the result is a comparison rather than a bare measurement.Abstract, sentence 4
Two possible scaling laws are derived from the experimental data, each correlating the thermal deposition on the electrode with the energy stored in the bank.Abstract, sentence 5
A fraction of about ten per cent of the total energy is released to the inner electrode.Abstract, sentence 6
What to watch: after setting out the cooling and heating mechanisms the authors analyse the maximum temperature the electrode materials can sustain, which turns the ten per cent figure into the design question for a repetitive machine — how fast heat can be pulled back out of the inner electrode between shots. The number to watch in this line of work is the sustained repetition rate a cooled electrode survives at a given bank energy.Abstract, final sentence, read against sentences 1 and 6
The way in
https://doi.org/10.1088/0963-0252/15/1/014How to cite it
E. Angeli, M. Frignani, S. Mannucci, F. Rocchi, M. Sumini, A. Tartari (2006) The heating of plasma focus electrodes doi:10.1088/0963-0252/15/1/014