Investigation of a spherical plasma focus concept as a neutron and bremsstrahlung radiation source

Plasma Focus device with two concentric spherical electrodes is proposed as a pulsed neutron and Bremsstrahlung radiation source. This spherical plasma focus system is modeled herein, which is different from the traditional cylindrical plasma focus. While a snow plow model and shock wave equations coupled with the circuit equations were used for investigating the general characteristics of the spherical plasma focus, however, the beam-target neutron yield mechanism was used for neutron production in addition to the inclusion of the emitted radiations in Bremsstrahlung, line radiation and radiative recombination from the plasma column, and the joule heating mechanism. Plasma-ion density, beam-ion density and beam-ion speed were also calculated under the assumed diode voltage in the radiative phase of the spherical plasma focus. Model validation was done by comparing the model results to the published experimental ones, and good agreement was obtained between the developed model and the experimental results.

The variations in the gas pressure and discharge voltage were used separately to investigate the effect of the different molecular weights, gases and discharge voltage on the plasma parameters. A 1:1 deuterium — tritium mixture was used to investigate the neutron yield, ion properties, emitted radiations and plasma resistance. The study predicted a peak discharge current of 1.50 MA for tritium with 0.92 MA dip discharge current, and less for deuterium and hydrogen. The current drop for tritium indicates a good focus action and that the sheath velocity for heavy gases is lower than lighter gases. Predicted maximum temperature was about 11.1 eV for hydrogen, 14.6 eV for deuterium, 15.9 eV for DT mixture and 17 eV for pure tritium; which indicated higher temperature with heavier gasses. While the achieved neutron yield was 1.13×1013 per pulse under the maximum diode voltage of 45.37 kV, the maximum plasma-ion density, beam-ion density and – eam-ion speed were 1.62×1024 m3, 6.84×1020 m3 and 208.44 cm/μs, respectively. The plasma resistance was increased from 0.06 mΩ to 0.26 mΩ which is a factor of 4.3 higher resulting in higher joule heating.

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