Focussing Protons from a Kilojoule Laser for Intense Beam Heating using Proximal Target Structures

C Mcguffey,P Fitzsimmons,M S Wei,J Kim,S N Chen,M E Foord,H S Mclean,P M Nilson,R B Stephens,P K Patel,F N Beg,D Mariscal,J Fuchs

doi:10.1038/s41598-020-65554-4

Abstract

Proton beams driven by chirped pulse amplified lasers have multi-picosecond duration and can isochorically and volumetrically heat material samples, potentially providing an approach for creating samples of warm dense matter with conditions not present on Earth. Envisioned on a larger scale, they could heat fusion fuel to achieve ignition. We have shown in an experiment that a kilojoule-class, multi-picosecond short pulse laser is particularly effective for heating materials. The proton beam can be focussed via target design to achieve exceptionally high flux, important for the applications mentioned. The laser irradiated spherically curved diamond-like-carbon targets with intensity 4 × 1018 W/cm2, producing proton beams with 3 MeV slope temperature. A Cu witness foil was positioned behind the curved target, and the gap between was either empty or spanned with a structure. With a structured target, the total emission of Cu Kα fluorescence was increased 18 fold and the emission profile was consistent with a tightly focussed beam. Transverse proton radiography probed the target with ps order temporal and 10 μm spatial resolution, revealing the fast-acting focussing electric field. Complementary particle-in-cell simulations show how the structures funnel protons to the tight focus. The beam of protons and neutralizing electrons induce the bright Kα emission observed and heat the Cu to 100 eV.

Highlights

High-intensity proton beams generated by ultrashort pulse laser-matter interactions[1,2,3] were immediately recognized as a powerful tool for the creation of Warm Dense Matter (WDM)[4,5]
Proton focussing measurements were taken for the first time in the kiloJoule regime at the OMEGA EP facility using a 1.25 kJ, 10 ps short pulse laser along with proton spectrum measurements using a Thomson parabola diagnostic named Thomson Parabola Ion Energy Analyzer (TPIE)
Due to the protons’ velocity dispersion, different energy protons probed the interaction plane at different delays. They were discriminated by energy using a stack of RadioChromic Film (RCF) detectors

Summary

Introduction

High-intensity proton beams generated by ultrashort pulse laser-matter interactions[1,2,3] were immediately recognized as a powerful tool for the creation of Warm Dense Matter (WDM)[4,5] These beams have since found widespread use in High Energy-Density physics studies as isochoric heaters that allow study of conditions similar to those in the interior of planets[6], as probes of complex objects[7] and of transient electric and magnetic fields[8,9,10,11] with micron scale resolution[12], or for inducing nuclear reactions to create directional neutron beams[13,14]. The high energy and pulse duration of the OMEGA EP drive laser produced a proton beam that, when focussed, achieved exceptionally high peak beam density This dramatically increases the prospects for using protons for isochoric heating and the intensity-hungry applications mentioned above.

Methods

Results

Conclusion