Mega-Ampere (MA) pulsed power generators are one of the essential drivers to create high energy density plasmas for plasma physics, laboratory astrophysics and inertial confinement fusion research. The pulsed power current can produce a slowly rising pressure ramp that compresses a solid material to a high density without significant heating. Material properties of such high density, low temperature plasmas known as warm dense matter (WDM) are critical information in models for the interior of giant planets and laser fusion cores. Most pulsed power WDM experiments are conducted in a planar geometry at a large facility because of a well-established optical diagnostic available and tens of MA of current required for high compression. Alternatively, cylindrical compression is an attractive approach because of its high compressibility than that in the planar geometry and its direct relevance to the magnetized liner inertial fusion concept. However, the dense cylinder shape plasma requires a hard x-ray or energetic charged particle source to diagnose the plasma condition. 

The objective of this experimental program is to develop and demonstrate short-pulse laser-based diagnostics for pulsed power-driven cylindrically compressed wires using a 50 TW short-pulse laser Leopard and a 1 MA pulsed power generator Zebra at the University of Nevada Reno. A millimeter-diameter metal wire will be cylindrically compressed by the Zebra current with a ~100 ns rise time, while the Leopard laser will irradiate a metal target to produce hard x rays that can penetrate into the high-density wire. In this work, we will specifically focus on development of high-resolution x-ray radiography using broadband and monochromatic x rays. Broadband x-ray radiography (> 20 keV) will produce high quality x-ray images providing information on the diameter and density of the compressed wire. Monochromatic x-ray imaging with a spherically bent crystal will enable more accurate density measurements than the broadband x-ray imaging. The temporal evolution of the wire density will be obtained by varying the laser timing with respect to the pulsed power current. Systematic data sets of the wire plasmas will be collected for various wire diameters, materials, and thicknesses of plastic coating on the wire.

This program will produce a variety of invaluable experimental and technical data addressing both the feasibility of short-pulse laser-based x-ray radiography and the WDM creation capability with the cylindrical compression scheme. The experimental data on the compressed density and wire diameter could be used for benchmarking magnetohydrodynamics simulation codes. Successful demonstration of the cylindrical compression to create WDM on Zebra could promote pulsed power-driven WDM research at university scale and next generation repetitive pulsed power facilities combined with high-power lasers. This program will also support local undergraduate and graduate students to gain a variety of hands-on training experience including participation of the experiments, data collections and analyses.