An Imaging Refractometer for Density Fluctuation Measurements in High Energy Density Plasmas

TL;DR

This paper introduces a novel laser-based imaging refractometer capable of measuring density fluctuations in high-energy-density plasmas by analyzing laser beam deflections, offering enhanced sensitivity over traditional methods.

Contribution

The paper presents a new diagnostic technique combining imaging and angular deflection measurements for high-energy-density plasmas, validated through synthetic and experimental data.

Findings

Enhanced sensitivity over standard shadowgraphy and schlieren imaging.

Able to measure angular deflections from 0.06 to 34 mrad.

Demonstrated application in turbulence behind a reverse shock.

Abstract

We report on a recently developed laser-probing diagnostic which allows direct measurements of ray-deflection angles in one axis, whilst retaining imaging capabilities in the other axis. This allows us to measure the spectrum of angular deflections from a laser beam which passes though a turbulent high-energy-density plasma. This spectrum contains information about the density fluctuations within the plasma, which deflect the probing laser over a range of angles. %The principle of this diagnostic is described, along with our specific experimental realisation. We create synthetic diagnostics using ray-tracing to compare this new diagnostic with standard shadowgraphy and schlieren imaging approaches, which demonstrates the enhanced sensitivity of this new diagnostic over standard techniques. We present experimental data from turbulence behind a reverse shock in a plasma and demonstrate that this technique can measure angular deflections between 0.06 and 34 mrad, corresponding to a dynamic range of over 500.