Single-shot 256-frame Radiography Measurements of Pulsed Power Driven Instability Growth in Converging and Diverging Geometries

The dynamics of HED plasmas are dominated by instabilities - in astrophysics, these govern the structure of protostellar jets and nebulae; on Earth, the success of ICF experiments depends on the reduction of mixing of cold, dense, high Z plasma into fusion fuel. Measuring the evolution of hydrodynamic instabilities is vital to quantitative validation of theory and simulations, yet many experiments are limited to exploring a small region of parameter space, or provide only few measurements per experiment, requiring control of the initial conditions.

In this presentation, we describe a novel technique to obtain 256 radiographs (176ns apart, 8μm resolution, 100ps exposure) of hydrodynamic evolution in a single shot. We use a compact pulsed power driver (35kA, 1000ns rise time) to resistively explode underwater metallic assemblies and drive convergent, divergent, or planar shocks at multi-km/s speeds. The driver is coupled to the X-ray phase contrast imaging (E~30keV) of the European Synchrotron Radiation Facility.

Initially, we studied the axial density striations induced by the electrothermal instability (ETI) in exploding wires. Here we measured the interaction of a cylindrically convergent shock travelling from the surrounding water into low density plasma of an exploding wire (negative Atwood number), revealing the wavelengths of the density perturbations in the wire plasma. The ETI dynamics were used to control the density perturbations in the plasma by changing the wire material (Al, Ag, Cu, Mo, W). The results of the experiments agree with the ETI theory and provide a test for the conductivity and EoS models used in MHD simulations.

We will also discuss the design and results of the thin-layer Richtmyer-Meshkov instability measurements, scaling of the experiments, and results from simulations performed in the GORGON MHD code.