Investigation of Proton Beam-Driven Fusion Reactions Generated by an Ultra-Short Petawatt-Scale Laser Pulse

Published by M.S. Schollmeier, V. Shirvanyan, C. Capper, S. Steinke, A. Higginson, R. Hollinger, J.T. Morrison, R. Nedbailo, H. Song, S. Wang, J.J. Rocca, G. Korn, in Laser and Particle Beams

This work presents results from a pitcher-catcher experiment utilizing a proton beam generated with nanostructured targets at a petawattclass, short-pulse laser facility to induce proton-boron fusion reactions in a secondary target. A 45-fs laser pulse with either 400 nm wavelength and 7 J energy, or 800 nm and 14 J, and an intensity of up to 5 ×10²¹ W/cm² was used to irradiate either thin foil targets or near-solid density, nanostructured targets made of boron nitride (BN) nanotubes. In particular, for 800 nm wavelength irradiation, a BN nanotube target created a proton beam with about five times higher maximum energy and about ten times more protons than a foil target. This proton beam was used to irradiate a thick plate made of boron nitride placed in close proximity to trigger ¹¹B (p, α) 2α fusion reactions. A suite of diagnostics consisting of Thomson parabola ion spectrometers, postshot nuclear activation measurements, neutron time-of-flight detectors, and differentially filtered solid-state nuclear track detectors were used to measure both the primary proton spectrum and the fusion products. From the primary proton spectrum, we calculated (p, n) and (α,n) reactions in the catcher and compare with our measurements. )e nuclear activation results agree quantitatively and neutron signals agree qualitatively with the calculations, giving confidence that primary particle distributions can be obtained from such measurements. These results provide new insights for measuring the ion distributions inside of proton-boron fusion targets.

Experiment layout

Feutured4a A sketch of the target chamber with the relevant diagnostics. The laser pulse is focused by an f/2 off-axis parabolic mirror to an intensity of ∼5 × 10²¹ W/cm² onto a target at the center of the chamber. Thomson parabola (TP) ion spectrometers are used to diagnose the generated proton beam. A filtered CR39 solid-state nuclear track detector is used to corroborate the TP measurements. A neutron time-of-flight (nTOF) detector is placed in about 3 m distance along the target normal direction. The inset in the lower-left corner shows a photograph of the target holder.