Analysis of Supersonic Shock-Diamond Jets in Gas Puff Flow for a Dense Plasma Focus Accelerator

Gas puff injection can improve the production of neutrons by nuclear fusion in a dense plasma focus accelerator by increasing the density of gas at the pinch. A Schlieren imaging system has been used to visualize the supersonic shock-diamond pattern in the jet emanating from a Mach 8 gas puff nozzle using deuterium gas. This pattern is stationary during the duration of the gas puff and the density variation in the gas throughout the jet is of interest due to its interaction with the magnetic pinch where fusion occurs. An analytical procedure is presented that models the density, pressure, and temperature variation in a supersonic jet by following the intersections of Prandtl-Meyer expansion fans, oblique shocks, and the free surface of the jet. The results are compared with oblique shock and expansion fan angles measured from Schlieren images through multiple Mach disks. This method is applicable to both over and under expanded supersonic jet flows. The results of this model can be used to assess the changes in thermodynamic gas properties in the supersonic jet, as well as the local Mach number and the index of refraction of the jet along the central axis. The model is being used to estimate the increased density of gas in the pinch that leads to increased neutron production.