The plasma focus is a relatively inexpensive device that is known to produce fusion reactions. As such, it has been used to study plasma physics in various countries that don’t have the budgets for more expensive fusion devices. It has also been studied for applications in X-ray lithography, neutron therapy, medical istope production, and production of neutrons for nuclear weapons. Thirty or so years ago, when fusion budgets were being reduced and the tokamak was edging out the competition, it was widely believed (and still is today among most mainstream fusion researchers) that the plasma focus produces fusion primarily by a beam-target mechanism in which the ion beam collides with cold gas in the chamber, producing fusion reactions. And indeed, there is evidence that in some devices that is the case. If that is always so, prospects are not good for the plasma focus as a net power fusion device. Eric Lerner is convinced, based on his own study of the plasma focus device, that in the right configuration it can produce fusion primarily by a thermonuclear mechanism within the plasmoid. Based on experiments he conducted at Texas A&M in 2001, he published a paper demonstrating the production of neutrons and hard X-rays within the plasmoid itself (see note 25 and figure 1 in particular). However, my impression is that these results have not yet been widely accepted within the plasma physics community.
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