The central mystery of plasma focus research is the two
orders-of-magnitude-higher-than-thermal fusion reaction rate and the fact that both the space-resolved neutron spectra and space-resolved
reaction proton spectra show features which can be ascribed only to a rotational motion of the
center-of-mass of the reacting deuteron population. It has been suggested earlier
[S. K. H. Auluck, IEEE Trans. Plasma Sci. 25, 37 (1997)] that this and other experimental observations can be
consistently explained in terms of a hypothesis involving rotation of the current carrying plasma
annulus behind the imploding gas-dynamic shock. Such rotation
(more generally, mass flow) is an in-built feature of relaxed state of a two-fluid plasma
[R. N. Sudan, Phys. Rev. Lett. 42, 1277 (1979)]. Relaxation in the “Hall magnetofluid” approximation, in which the generalized Ohm’s law
includes the Hall effect term and the magnetic convection term but omits the contributions to the
electric field from resistive dissipation, electron pressure gradient, thermoelectric effect, electron
inertia, etc., has been extensively studied by many authors. In the present paper, Turner’s
[IEEE Trans. Plasma Sci. PS-14, 849 (1986)] degenerate solution for the relaxed state of the Hall
magnetohydrodynamic plasma has been adapted to the case of an infinitely long annular current
carrying plasma, a tractable idealization of the current sheath of a plasma focus. The resulting model
is consistent with experimental values of ion kinetic energy and observation of predominantly
radially directed neutron emission in good shots.
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