Imaging Refractometry Technique Development

The imaging refractometry technique is a valuable diagnostic tool for studying high-energy-density plasmas. Density fluctuations in these plasmas are challenging to measure, particularly in gas-puff Z-pinch implosions where turbulence is thought to be present [1,2,3] and in a Pulsed Magnetic Fusion environment in general. After its introduction [4], the technique has been further developed at Cornell’s Laboratory of Plasma Studies [5] for diagnosing imploding gas-puff Z-pinch plasmas using a 40 mJ, 150 ps, frequency-doubled Nd:YAG laser pulse at 1064/532 nm.

The imaging refractometer technique measures the phase correlations of the probing laser field and is sensitive to the density gradients within the plasma. We propose the novel statistics-based approach [6] for a case where the turbulent layer is thick enough to generate laser speckles. In this analysis, the probability distribution, speckle contrast, and autocorrelations are studied.

The PERSEUS 3D Extended MHD code [7] along with the Beam Propagation method simulation [8] is employed to study synthetic data. Moreover, the PERSEUS code is run on the Bridges-2 system [9] to obtain a high spatial resolution to be further analyzed with the BPM code.