Historical research guide · 0885 · 2002
Review of Recent Experiments with the Megajoule PF-1000 Plasma Focus Device
H Schmidt · A Kasperczuk · M Paduch · T Pisarczyk · M Scholz · K Tomaszewski · A Szydłowski
In one minute
PF-1000 is one of the largest plasma focus machines ever built: a megajoule capacitor bank discharged down a pair of coaxial electrodes, driving a sheet of current that sweeps gas ahead of it and then collapses onto the axis into a dense, self-holding pinch. Schmidt, Scholz and their co-authors report what the machine did once it ran at its full energy. Each shot produced more than two hundred billion fusion neutrons. They watched the discharge with voltage and current monitors, with soft and hard X-ray detectors and with neutron detectors, and measured neutron energies with a scintillator and photomultiplier placed 85 metres upstream of the machine. Two results stand out. The neutrons often arrive in two or more bursts about two microseconds apart rather than in one. And the fastest of them carry 2.95 million electronvolts — measurably more than the 2.45 million a deuterium-deuterium reaction releases at rest, the signature of nuclei fusing while already moving fast along the axis toward the detector.
Connection
Chapter 9 says self-organising plasma is thriving, established physics, and the plasma focus is its industrial-scale worked example: a current sheet that folds itself into a dense knot and makes fusion neutrons every shot. Chapter 12 needs the energy substrate, and this paper is a full megajoule of it, measured — with an upstream neutron spectrum that shows the reacting ions are directed, not merely hot.
From the source
PF-1000 was operated successfully in the Mather-type plasma focus mode at the 1 megajoule energy level. That is the full-scale energy storage the machine was built for, and the paper is the review of what it produced there.Abstract, opening sentence
The neutron yield exceeded 2 times 10 to the eleventh per shot — more than two hundred billion fusion neutrons from a single discharge.Abstract, opening sentence
The shots were instrumented on several channels at once: temporal monitoring of voltage and current, soft X-ray detection, hard X-ray detection, and neutron detection. Neutron spectra were measured with a scintillator and photomultiplier detector positioned 85 metres upstream of the device, the long flight path being what makes a time-of-flight energy measurement possible.Abstract, second and third sentences
The emission is not a single event. Two or more neutron pulses, separated by about 2 microseconds, were often registered in one shot — so the pinch delivers its neutrons in repeated bursts rather than in one collapse.Abstract, fourth sentence
The maximum neutron energy measured upstream was 2.95 plus or minus 0.15 million electronvolts, which the authors note is appreciably higher than the 2.45 million electronvolts carried by a neutron from a deuterium-deuterium reaction between nuclei at rest. The excess is measured, and it is the quantity that distinguishes directed ion motion along the axis from simple thermal energy in the plasma.Abstract, fifth sentence
What to watch: the authors name their own open question. The reason for the multiple X-ray and neutron pulses is possibly re-breakdown in the insulator region at pinch time, and it has to be further investigated — so the measurement that settles it is a diagnostic that images the insulator region at the moment of the pinch, on the same shots that record the neutron bursts.Abstract, final sentence
The way in
https://doi.org/10.1238/physica.regular.066a00168How to cite it
H Schmidt, A Kasperczuk, M Paduch, T Pisarczyk, M Scholz, K Tomaszewski, A Szydłowski (2002) Review of Recent Experiments with the Megajoule PF-1000 Plasma Focus Device doi:10.1238/physica.regular.066a00168