Distortions in Charged-Particle Images of Laser Direct-Drive Inertial Confinement Fusion Implosions

TL;DR

This paper investigates distortions in charged-particle images from inertial confinement fusion experiments, proposing a filamentary scattering model that explains the distortions and impacts other diagnostics.

Contribution

It introduces a new filamentary scattering model to explain charged-particle image distortions in ICF diagnostics and demonstrates its effectiveness through particle-tracing simulations.

Findings

Filamentary electric/magnetic fields cause significant image distortions.

The scattering model reproduces observed image distortions.

Impacts of filamentary fields extend to other charged-particle diagnostics.

Abstract

Energetic charged particles generated by inertial confinement fusion (ICF) implosions encode information about the spatial morphology of the hot-spot and dense fuel during the time of peak fusion reactions. The knock-on deuteron imager (KoDI) was developed at the Omega Laser Facility to image these particles in order to diagnose low-mode asymmetries in the hot-spot and dense fuel layer of cryogenic deuterium--tritium ICF implosions. However, the images collected are distorted in several ways that prevent reconstruction of the deuteron source. In this paper we describe these distortions and a series of attempts to mitigate or compensate for them. We present several potential mechanisms for the distortions, including a new model for scattering of charged particles in filamentary electric or magnetic fields surrounding the implosion. Particle-tracing is used to create synthetic KoDI data based on the filamentary field model that reproduces the main experimentally observed image distortions. We conclude that the filamentary scattering model best matches the observed image distortions. Finally, we discuss potential impacts of filamentary fields on other charged-particle diagnostics.