Detecting Solenoidal Plasma Turbulence via Laser Polarization Rotation

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.

Figures (2)

• Figure 1: Random walk of the polarization angle $\psi$ as the laser beam traverses multiple uncorrelated turbulent eddies, leading to an rms broadening $\psi_{\text{rms}}$.
• Figure 2: Randomly oriented eddies of a characteristic size $l_{\text{eddy}}$ produce a diffraction cone. A distribution of rings is formed behind a cross-polarization filter, analogous to a Debye-Scherrer ring.