Reconstruction of 2D line-integrated electron density using angular filter refractometry and a fast marching Eikonal solver

TL;DR

This paper introduces a novel method combining angular filter refractometry with a fast marching Eikonal solver to accurately reconstruct 2D line-integrated electron density from plasma measurements, validated through synthetic and experimental data.

Contribution

It presents the first direct inversion technique for AFR data to obtain 2D electron density using a fast marching Eikonal solver, improving analysis over prior 1D or forward-fitting methods.

Findings

Reconstructed densities match 1D results.

Method is validated with synthetic data.

Experimental results are consistent with AFR measurements.

Abstract

Refraction of an optical probe beam by a plasma can be measured with angular filter refractometry (AFR), which produces an image containing intensity contours that correspond to curves of constant refraction angle. Further analysis is required to reconstruct the underlying line-integrated electron density. Most prior efforts to calculate density from AFR data have been limited to 1D analysis or forward-fitting techniques. In this paper, we detail the use of a fast marching Eikonal solver to directly invert AFR data and obtain the 2D line-integrated electron density. The analysis method is first verified with synthetic data and then applied to laser-driven experiments of single and double plume expansion collected at the OMEGA EP Laser Facility. The calculated densities agree with 1D results and are shown to be consistent with the original AFR measurements via forward modeling. We also discuss how additional measurements could improve the precision of this technique.