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  6. Inferring Heat Flow in Laser Absorption Regions using Diagnostic Magnetic Fields

Inferring Heat Flow in Laser Absorption Regions using Diagnostic Magnetic Fields

Christopher Walsh | 21-FS-051

Project Overview

This research was motivated by the desire to obtain a measurement of heat flow in overdense regions of a laser-ablated plasma for the first time using a high-energy proton beam. For sufficiently high energies, the proton beam can pass through overdense regions and only be deflected by electric and magnetic fields. As the transport of magnetic fields in a plasma are intrinsically linked to the transport of thermal energy, it was posited that such a measurement could be used to infer a heat flow. While the project did not prove the method to be infeasible, difficulties with understanding the proton radiographs without an imposed magnetic field made the final aim of this project unreached. Instead, however, a closer understanding of proton radiographs of laser-solid interactions without an imposed field has been obtained. Five shot days on the OMEGA laser facility have been awarded (three through ICF and two as ride along) to further investigate some of these features. Extrapolating current results to hohlraum conditions has the magnetic energy being a significant (10%) fraction of the laser drive energy, which has the potential to explain the NIF hohlraum drive deficit.

Mission Impact

Our results directly impact the ICF mission to understand conditions inside the hohlraum. In particular, a new hypothesis for the hohlraum drive deficit was proposed and four further experiments are scheduled.

Publications, Presentations, and Patents

Walsh, Chris. "Magnetic Fields in Laser-Plasma Interactions." Presentation. 49th IEEE International Conference on Plasma Science. Seattle, WA. May 2022.

Tubman, Ellie. "Dual Axis Radiography of Laser-Plasma Interactions." Poster. 49th IEEE International Conference on Plasma Science. Seattle, WA. May 2022.

Walsh, Chris. "Magnetic Fields in Laser-Plasma Interactions." Poster. OMEGA Laser Facility User Group 2022 Workshop. Rochester, NY. April 2022.

Tubman, Ellie. "Dual Axis Radiography of Laser-Plasma Interactions." Poster. OMEGA Laser Facility User Group 2022 Workshop, Rochester, NY. April 2022.