Articles you may be interested inRepetitive Nanofocus: Evidence of neutron and xray emission from an ultra miniature pinch plasma focus discharge operating at tens of Hz AIP Conf. Proc. 996, 72 (2008); 10.1063/1.2917033Focusing and dispersing properties of a stigmatic crossedfield energy analyzer
A model has been developed for the acceleration of deuterons in the tightly compressed column of a z-pinch discharge, in particular, that of a plasma focus discharge. It was assumed that an annular distribution of current undergoes a rapidly contracting transition to a distribution peaked on axis and the resulting crossed fields, Bθ and Ez, were used to calculate deuteron trajectories in the plasma. These results show that a significant number of ions can be accelerated to energies of up to 600 keV and that they have a large value for their time-averaged axial velocities. The orbiting motion in the magnetic field produces an anisotropic distribution of collision velocities and a neutron-production model based upon nuclear collisions by these deuterons can account for the measured characteristics of neutron energies, neutron fluxes, and rates of production.
The efficiency of converting focused laser radiation into kilovolt x rays by means of a high-z planar plasma has been calculated. For electron temperatures of several keV, the rapid expansion of the plasma limits the effective absorption and reradiation times to a few tenths of a nanosecond. This short time limits the fractional degree of ionization to 30%–60%, depending on the temperature, for heavy target ions such as gold, and in this case the predominant ions have ionization energies less than the electron temperature. For plasma temperatures of 3 up to 10 keV the total radiation output will range from 6 down to 2 times that of plasma bremsstrahlung alone. The conversion efficiency is relatively insensitive to the laser frequency and to the plasma temperature, and amounts to 2%–5%. Overall efficiency for a Nd-glass laser system turns out to be about 10−3.
The energy spectrum and spatial distribution of neutrons emitted by a plasma focus device were measured with nuclear emulsions and scintillation detectors, and the results are reported. The average energy of the D-D neutrons emitted along the axis was shifted ∼500 keV corresponding to an axial center-of-mass velocity of 2 × 108 cm/secfor the reacting deuterons. An 11% anisotropy in the neutron fluxes measured in the forward and radial directions correlates with an axially streaming plasma which is not isotropic; the reacting deuterons collide predominantly in the radial direction. Time-resolved collimation measurements of the emitted neutrons showed an axial translation of the neutron source corresponding to velocities up to 2 × 108 cm/sec; this correlates with the nonsimultaneous pinching of the noncylindrical plasma along the axis. Plasma densities of ∼ 2 × 1020cm−3 and ion temperatures of 2 keV were consistent with observed neutron yields of 1010 and pulse widths of 60 nsec. X-ray intensity measurements were made for x-ray energies of 7 < Ep < 30 keV and showed an Ep−2 dependence which does not agree with plasma bremsstrahlung, but appears to result from anode bombardment of axially accelerated electrons with energies > 200 keV. The line radiation corresponded to that of fairly cold ions.
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