Solid fibre Z-pinches two-dimensional computations and laboratory diagnostic interpretation

Los Alamos National Laboratory, Los Alamos, New Mexico-Experiments at Los Alamos, the Naval Research Laboratory, Imperial College, and elsewhere have demonstrated that interesting, long-lived fusion plasmas can be created by discharging modern high-voltage pulsed power generators through frozen deuterium fibers or solid fibers of other materials. We have performed one- and two-dimensional magnetohydrodynamic computations of the formation and evolution of fiber-formed plasmas. Our computations use "cold-start" initial conditions in an attempt to compute the behavior of the pinches from t=0. Our one-dimensional computations show that, prior to complete fiber ablation, current is carried by low-density, hot plasma which has been ablated from the fiber; the computations predict that the fiber persisted longer than expected in early experiments. Our two-dimensional computations predict m=0 behavior of the fiber-formed pinches. The m=0 behavior begins in the hot, exterior plasma prior to complete ablation of the fiber; the m=0 behavior enhances the fiber ablation rate. Although interpretation of experimental diagnostics to detect such instability remains controversial, we find that "diagnostics" based on the computed two-dimensional density /temperature profiles agree qualitatively and quantitatively with essentially all experimental observations at several different laboratories. Diagnostics considered include x-ray and visible light emission, neutron production, shadowgraphy, and interferometry. The computations show an axial variation in electron line-density due to the m=0 behavior, consistent with recent Los Alamos interferometric measurements.