Experimental study of the neutron emission mechanisms in a Filippov-type plasma focus device

Abstract

The results of an experimental investigation of neutron emission characteristics in the Filippov-type plasma focus facility "Dena" (90 kJ, 25 kV, 288 µF) with D2 + %1 Kr as working gas are presented. From the experimental results, one can conclude that both thermonuclear and nonthermonuclear mechanisms are always present in neutron production, but their contributions to the total neutron yield are strongly dependent on the initial pressure and discharge voltage. It has been found that at constant discharge voltages and low pressures the beam-target interaction mechanism plays an important role in the neutron production and with increasing the pressure, its role decreases and the importance of thermonuclear mechanism increases. Also at constant pressures, the contribution of beam-target interaction mechanism in neutron production decreases with increasing the discharge energy. The value of the α index in the empirical neutron yield scaling law Yn ∝ I α ∝ E α/2 was found to be about 3.82.

Search for thermonuclear neutrons in a mega-ampere plasma focus

“…In order to verify the thermonuclear mechanism, it seems appropriate to observe the time and duration of neutron production. The temporal evolution of neutron production is often compared with soft and hard x-ray (HXR) emission [26][27][28]. Thermonuclear neutrons are expected to be accompanied by intensive soft x-ray (bremsstrahlung) radiation during the maximum compression.…”

Experimental results of breakdown in "Dena" plasma focus device

“…A schematic diagram of "Dena" with all of its diagnostics is shown in Figure1. The description of this device has been reported completely elsewhere [13]. The diagnostic system consists of a 4-channel PC-based data acquisition system including two GPIB compatible oscilloscopes (50MHz) and two fast (500MHz) digital storage Tektronix oscilloscopes.…”

“…In general, the different phases of discharge in Plasma Focus devices can be divided to five different stages [1,2,3,8,12]: 1 -The initial breakdown and surface discharge , very little is known about the physics of this phase [13], this phase has a great influence on the formation of final pinch , 2 -rundown phase that does not exist in Filippov-type devices, 3 -radial compression , 4 -pinch phase , 5 -instability happening and pinch destruction. In this paper we would present and analyze the results of initial breakdown & surface discharge phase in "Dena" Filippov-type Plasma Focus Facility (90 kJ, 25 kV) in different working conditions.…”

Pinched Plasma Study in a Filippov-Type Plasma Focus “Dena”

“…The neutron emission anisotropic factor A = Φ n (0 • )/Φ n (90 • ), in which Φ n (0 • ) and Φ n (90 • ) are the neutron fluxes in the axial and radial directions with respect to the anode axis, respectively, is about two for the operational conditions of the Dena PF [2].…”

“…The soft X-ray (electron Bremsstrahlung in the thermal plasma) and the hard X-ray (which belong to the nonthermal interaction of the electron beam with the anode surface) are the signatures of these two mechanisms. However, at low pressure (less than 1 torr) and/or low discharge energies (less than 20 kJ), the nonthermal interaction mechanism plays an important role in the neutron production for the Dena PF [2]. This behavior may be explained by the well-known acceleration of the deuterons in the axial direction at low pressure due to the lower electron and gas densities in the plasma and in the surroundings, respectively.…”