High Energy Density Z-Pinch Plasmas using Flow Stabilization: ZaP-HD

Michael P. Ross, University of Washington
July 22, 2016, 12:00pm, SERF 232

ABSTRACT:

The ZaP-HD Flow Z-Pinch project provides a platform to explore how shear flow stabilized Z-pinches could scale to high-energy-density plasma (HEDP) and fusion reactor conditions.  ZaP-HD generates shear stabilized, axisymmetric Z-pinches with stable lifetimes approaching 60 μs. The goal of the project is to increase the plasma density and temperature compared to the previous ZaP project by compressing the plasma to smaller (radii ≈ 1 mm). Radial and axial plasma electron density structure is measured using digital holographic interferometry (DHI), which provides the necessary fine spatial resolution.  ZaP-HD's DHI system uses a 2 ns Nd:YAG laser pulse with a second harmonic generator (λ = 532 nm) to produce holograms recorded by a Nikon D3200 digital camera. The holograms are numerically reconstructed with the Fresnel transform reconstruction method to obtain the phase shift caused by the interaction of the laser beam with the plasma. This provides a two-dimensional map of line-integrated electron density, which can be Abel inverted to determine the local number density. The DHI resolves line-integrated densities down to 3 X 10²⁰ m^-2 with spatial resolution near 10 μm. This talk presents the theory and implementation of Fresnel transform reconstruction. A study of synthetic data analyzes the method's accuracy, and an Abel inversion procedure is exhibited that utilizes experimental data on both sides of a Z-pinch local number density profile to maximize profile symmetry.  A uniform drift velocity model is applied to compute the Z-pinch equilibrium from the measured density and wall magnetic field, which helps estimate the boundaries of ZaP-HD’s operating regime.