Space, Time, and Energy Distributions of Neutrons and X Rays from a Focused Plasma Discharge

Abstract

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.

Manifestation of Constrained Dynamics in a Low-Pressure Spark

“…Such broad side-on neutron spectra have also been observed in a frozen deuterium fiber z-pinch [6] and a gas-puff z-pinch [7]. • Neutron ToF spectra at 0° and 180° to the axis consistently show a shift towards higher and lower energy respectively [8,9,10,11]. A similar observation is also made in a gas puff pinch [12].…”

Axial magnetic field and toroidally streaming fast ions in the dense plasma focus are natural consequences of conservation laws in the curved axisymmetric geometry of the current sheath

“…However, what sort of fast ion population would give rise to observed properties of the neutron emission remains a subject of active research. A recent summary of the status [7] mentions the pioneering observations [33][34][35][36] The combination of reports of ions moving along the axis [33][34][35][36], moving radially [40], moving in loops in the plane comprising device axis and a horizontal line [41] , opposite to the axis [37][38][39] and around the axis [13,42] (over axially limited region) can be comprehensively described as representing toroidal motion [43]. The signature of such toroidal motion is predominantly seen in the width (and not the average energy which remains ~2.45 MeV for neutrons) of the space-averaged side-on neutron spectrum, and in the space space-resolved sideon neutron or fusion proton spectra.…”

Advancements in Dense Plasma Focus (DPF) for Space Propulsion

“…Pinch lifetimes, which are on the order of 150 ns, can possibly be made longer through the use of embedded magnetic fields that prevent instability modes. Since both hard and soft x-rays have been detected in experiments (Bernstein, 1969), broadband x-rays should be used. Advances in W/Si x-ray supermirrors (Joensen, 1997) show significant promise for the reflection of bremsstrahlung radiation.…”