Boron-Proton Nuclear-Fusion Enhancement Induced in Boron-Doped Silicon Targets by Low-Contrast Pulsed Laser

Abstract

We show that a spatially well-defined layer of boron dopants in a hydrogen-enriched silicon target allows the production of a high yield of alpha particles of around 109 per steradian using a nanosecond, low-contrast laser pulse with a nominal intensity of approximately 3×1016Wcm−2 . This result can be ascribed to the nature of the long laser-pulse interaction with the target and with the expanding plasma, as well as to the optimal target geometry and composition. The possibility of an impact on future applications such as nuclear fusion without production of neutron-induced radioactivity and compact ion accelerators is anticipated.

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Plain Language Summary

Nuclear fusion involving boron has garnered interest since the 1930s because of the process’s ability to produce copious numbers of alpha particles, which can in turn be used for generating fusion energy without producing neutron-induced radioactivity. We build on these previous experiments using boron dopants in hydrogen-enriched silicon and recover significantly higher alpha-particle counts than previous studies using only moderate-power lasers that are readily reproducible in industrial settings.

We assemble samples of boron-doped silicon and carefully control the placement and concentration of the dopants. The boron atoms are placed with a density of 1022cm−3 in a layer 100 nm thick, and a 500-J laser at the Prague Asterix Laser System is fired at the sample. The laser pulses are characterized by a relatively low intensity, low power, and a low-contrast intensity ratio. We measure the craters produced by alpha-particle nuclear-track detectors. We verify that undoped silicon samples produce no alpha particles. We use a silicon carbide detector and a Thomson parabola spectrometer to recover the ion-energy distributions. An alpha-particle distribution of 4–8 MeV with a peak around 4.5 MeV is measured. Our experimental setup yields an alpha-particle flux of over 109 particles per steradian, a 100-fold increase over previous studies. We attribute this increase to our use of both longer laser pulses (nanoseconds) than previous experiments (picoseconds) and the boron-doped silicon targets.

We have verified that it is possible to create a high-luminosity source with potential strategic applications in the field of laser nuclear fusion and the development of next-generation compact particle accelerators.