Abstract
Laser-driven neutron sources could offer a promising alternative to those based on conventional accelerator technologies in delivering compact beams of high brightness and short duration. We examine this through particle-in-cell and Monte Carlo simulations that model, respectively, the laser acceleration of protons from thin-foil targets and their subsequent conversion into neutrons in secondary lead targets. Laser parameters relevant to the 0.5 PW LMJ-PETAL and 0.6–6 PW Apollon systems are considered. Owing to its high intensity, the 20-fs-duration 0.6 PW Apollon laser is expected to accelerate protons up to above 100 MeV, thereby unlocking efficient neutron generation via spallation reactions. As a result, despite a 30-fold lower pulse energy than the LMJ-PETAL laser, the 0.6 PW Apollon laser should perform comparably well both in terms of neutron yield and flux. Notably, we predict that very compact neutron pulses, of ∼10 ps duration and ∼100 μm spot size, can be released provided the lead convertor target is thin enough (∼100 μm). These sources are characterized by extreme fluxes, of the order of 1023 n cm−2 s−1, and even ten times higher when using the 6 PW Apollon laser. Such values surpass those currently achievable at large-scale accelerator-based neutron sources (∼1016 n cm−2 s−1), or reported from previous laser experiments using low-Z converters (∼1018 n cm−2 s−1). By showing that such laser systems can produce neutron pulses significantly brighter than existing sources, our findings open a path toward attractive novel applications, such as flash neutron radiography and laboratory studies of heavy-ion nucleosynthesis.
Highlights
Neutron beams are commonly employed in scientific research, medicine, and industry for a wide range of applications.1 In practice, they are generated from nuclear reactions initiated by accelerator proton beams
These sources are characterized by extreme fluxes, of the order of 1023 n cm−2 s−1, and even ten times higher when using the 6 PW Apollon laser
They are generated from nuclear reactions initiated by accelerator proton beams
Summary
Neutron beams are commonly employed in scientific research, medicine, and industry for a wide range of applications. In practice, they are generated from nuclear reactions initiated by accelerator proton beams. Laser-generated neutrons have already been utilized for a variety of purposes, such as materials testing for fusion experiments, nondestructive imaging, and studies of equations of state via neutron resonance spectroscopy.8,9 Such neutron sources exploit laser-driven energetic protons (with current record high energies of ∼100 MeV), electrons, or gamma-ray photons as the primary drivers, with typical cross sections in the barn range.. To compensate for the short lifespan (in the millisecond range) of the intermediate isotopes, a minimum neutron flux >1020 n cm−2 s−1 is estimated to be necessary for the r-process to operate.21 This value is several orders of magnitude above the capability of conventional accelerator-based facilities (∼1016 n cm−2 s−1), and significantly larger than the current record high flux (∼1018 n cm−2 s−1) obtained with intense short-pulse lasers..
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