Investigation and Analysis of Neutron Emission Characteristics in "Dena" Plasma Focus Facility

Since the first experiments with plasma focus facilities in 1960's. These devices are known as intense sources of neutron when the working gas contains deuterium with a proper density. Most of the emitted neutrons are produced by D-D reactions, but the mechanism of these reactions is not still clear completely. In this paper, the results of experimental investigations of neutron emission characteristics in "Dena" plasma focus facility (Filippov type, 90 kJ, 25 kV) over a range of discharge voltages and pressures are presented. Out working gases are D2 & D2+%1 Kr, two different conic and flat insert anodes were employed. We have simultaneously measured the total emissions in our experiments for analyzing the neutron generation mechanism in this device. We have found the upper & lower pressure limits and the optimum pressure for neutron generation, and we have observed the double pluses structure of neutron signal for the first time in this device. Form the experimental results, it seems that both thermonuclear & no thermonuclear mechanisms are always present in neutron generation, but their contribution in the total yield is strongly dependent on experimental conditions (initial pressure, discharge voltage, gas admixture, etc.) It was found that the range of variation of total neutron yield and neutron emission anisotropy factor for experiments with D2+%1 Kr is wider than experiments with D2, and the best neutron emission results belongs to discharges in D2+%1 Kr with a conic insert anode. By employing D2+%1 Kr with a conic insert anode, and varying pressure between 0.3-2 torr at a discharge voltage of 16 kV, it can be deduced that in low pressures (<0.5 torr) the role of beam - target interaction mechanism in neutron production is important, and its importance decreases with pressure, around the optimum pressure (0.86 torr) the GPM mechanism has the major effect on neutron generation, and at high pressures the thermonuclear mechanism plays the major role. Furthermore, the behavior of the neutron yield and anisotropy factor with discharge energy at a pressure near optimum (0.84 torr) was studied and it was found that at low energies anisotropy factor is relatively high and decreases sharply by increasing the energy, From the experimental results, the? index in the empirical neutron yield scaling law was found about 3.62 for D2 +%1 Kr and 3 for D2.