Investigation of proton-beam-driven fusion reactions generated by an ultra-short petawatt-scale laser pulse

We present results from a pitcher-catcher experiment utilizing a proton beam generated with nano-structured targets to induce proton-boron fusion reactions in a secondary target. A 45-fs, 5x10²¹ W/cm² laser pulse with 400 nm wavelength and 7 J energy, or 800 nm and 14 J, was used to irradiate either thin foil targets or near-solid-density, nano-structured targets made of boron nitride (BN) nanotubes. In particular, for 800 nm wavelength irradiation a BN nanotube target created a proton beam with about 5x higher maximum energy and about 10x more protons than a foil target. This proton beam was used to irradiate a BN plate placed in close proximity to trigger ¹¹B(p,α)2α fusion reactions. The primary spectrum was measured with a Thomson parabola ion spectrometer. Calculated (p,n) and (α,n) reactions in the catcher agree quantitatively with nuclear activation measurements; neutron time-of-flight data agree qualitatively, giving confidence that primary particle distributions can be obtained from such measurements. These results provide new insights for diagnosing the ion distributions inside an integrated proton-boron fusion device, such as for example the laser-driven, near-solid density, nano-structured micro-reactor concept [H. Ruhl, G. Korn, ArXiv 2202.03170, 2022].