Historical research guide · 0573 · 2004
Pinch evidence in a fast and small plasma focus of only tens of joules
Patricio Silva · Leopoldo Soto · Walter Kies · José Moreno
In one minute
A plasma focus is a beautifully simple machine: dump a capacitor bank into a pair of coaxial electrodes filled with gas, and the current sheet it drives runs down the barrel, folds over the end and collapses onto the axis into a dense, hot pinch. For decades that only worked in machines storing kilojoules to megajoules. Patricio Silva, Leopoldo Soto, Walter Kies and José Moreno built one storing tens of joules and showed that it still pinches. Their device is small and fast — a 160 nanofarad bank, 38 nanohenries of inductance, charged to between 20 and 35 kilovolts for 32 to 98 joules, with the current rising in about 150 nanoseconds — and the whole point of the design is that the energy density matches that of the big machines even though the stored energy is thousands of times lower. Running on deuterium at 50 and 67 joules they see both classic pinch signatures: the dip in the current derivative and the peak in the voltage.
Connection
Chapter 12 needs a compact, high-density plasma source that a small team can actually build and iterate on, and this paper is the measurement that moved the plasma focus from a hall-sized machine to a bench-sized one without giving up the plasma conditions. Chapter 9 studies self-organising, self-compressing plasma structures, and the pinch is the cleanest laboratory example of one.
From the source
A deuterium-filled plasma focus storing only tens of joules produces a pinch: the typical dip in the current derivative signal and the typical peak in the voltage signal — the same signatures associated with pinch compression in devices of 1 to 1000 kilojoules — were observed at 50 and 67 joules.Abstract, first and third sentences; title
The device is a fast, small system: a 160 nanofarad capacitor bank, 38 nanohenries of circuit inductance, charged between 20 and 35 kilovolts for a stored energy of 32 to 98 joules, with a current rise time of about 150 nanoseconds.Abstract, second sentence
The design rule the work demonstrates is that the quantity to hold constant when a plasma focus is scaled down is the energy density, not the stored energy: the small device maintains the same energy density as large devices while operating three to four orders of magnitude lower in stored energy.Abstract, second sentence
The time to pinch and the time to peak current were measured as functions of the deuterium filling pressure, giving the operating map a small plasma focus needs in order to be tuned to the pinch.Abstract, final sentence
The evidence presented here for the pinch is electrical — the current derivative dip and the voltage peak — so the measurement that extends the result is a direct fusion yield from a device of this size, which is the line of work the Chilean group carried forward into progressively smaller devices.Abstract, third sentence
The way in
https://doi.org/10.1088/0963-0252/13/2/020How to cite it
Patricio Silva, Leopoldo Soto, Walter Kies, José Moreno (2004) Pinch evidence in a fast and small plasma focus of only tens of joules doi:10.1088/0963-0252/13/2/020