Detecting Solenoidal Plasma Turbulence via Laser Polarization Rotation

TL;DR

This paper introduces a laser-based diagnostic method to directly measure solenoidal plasma turbulence, specifically vorticity and eddy size, in high-energy-density plasmas like those in NIF implosions.

Contribution

The authors propose a novel cross-polarization scattering technique that detects plasma vorticity and turbulence structure, filling a gap in existing diagnostics.

Findings

The method generates a cross-polarized signal proportional to turbulent vorticity.

A diffractive scattering signature reveals eddy size distribution.

Applicable to NIF implosion conditions and similar high-energy-density scenarios.

Abstract

Recent theoretical studies suggest that solenoidal turbulence can significantly enhance fusion reactivity, yet no standard diagnostic exists to directly measure these solenoidal flows in high-energy-density plasmas, nor to distinguish between solenoidal and compressional turbulence. We propose a method that directly diagnoses the energy and spatial structure of this rotational turbulence using the cross-polarization scattering of a probe laser. By coupling to the plasma vorticity, the scattering generates a cross-polarized signal proportional to the turbulent vorticity, effectively acting as a calorimeter for shear flows. We identify a diffractive scattering signature analogous to ``Debye-Scherrer ring'' that reveals the eddy size distribution. We show that this technique is applicable to National Ignition Facility (NIF) implosion conditions and other high-energy-density scenarios.