Boundary Conditions for Real Gas Puff Loads

Summary form only given. We have developed a model for treating, in a consistent manner, the measured gas puff distributions used in Z-pinches. This is important in order to model the Z-pinch dynamics in a way that does not introduce numerical excitations that interfere with the development of unstable Rayleigh-Taylor modes. The initial gas density distribution, measured by laser-induced fluorescence (PLIF), exhibits two-dimensional features even near its outer (radial) edges. For the 2D-MHD calculations performed using MACH2 it was found necessary to implement the model in order to apply the electromagnetic boundary conditions consistently. Without doing so, non-physical modes could be excited, leading to errors in the modeling of the Z-pinch implosion. In prior treatments the electromagnetic wave driving the plasma load has been assumed to be uniform across the discharge gap with electric and magnetic fields varying only in the direction tangential to the conducting walls of the vacuum feed. We have found that by applying an open circuit forward-going wave condition at a position removed from the plasma-vacuum interface and by inserting a vacuum transition region that permits the EM field to transform from a 1D to 2D character it is possible to treat the boundary conditions consistently. We illustrate the results obtained with calculations of the pinching process and compare the magnitude and wavelength changes brought about by the use of this method