Laser-driven charged particle acceleration mechanisms with relativistically intense pulses of ultrashort duration are reviewed for innovative low-density targets either of near critical or near relativistically critical densities. These targets being optimized over thickness and density for given laser intensity with 3D PIC simulations allow generate electrons with maximum total charge and protons with maximum energy. Applications of the generated high-energy electron and proton beams to nuclear and radiation sources are discussed.
We have extended recently published results of so-called SASL (synchronized acceleration by slow light) simulations to other relevant schemes of laser-plasma interaction for proton acceleration involving manipulation of laser polarization and parameters of low-density targets which are available in practice. In all cases, the main idea is to capture the protons from a target front side in the laser pulse ponderomotive electric field sheath and keep them synchronized with the latter due to specific nonlinear propagation and laser-target design. We have performed optimization study for given laser pulse energy to find the target which may produce protons with maximum possible energy.
The 3D PIC simulations performed have also demonstrated effective acceleration of electrons from low-density targets (inhomogeneous preplasma at the front of solid-dense foil and homogeneous near-critical plasma) in terms of the increased electron yield. It has been shown that homogeneous planar target with the density somewhat lower than a critical density is best suited for maximum total charge of high-energy electrons. This density, which is higher than a standard gas density for wakefield acceleration provides formation of laser field filled bubble, where electrons are stochastically accelerated in complicated firlds: longitudinal plasma field, focusing electrostatic field and laser field. The electron charge per shot with energies in excess of 100 MeV reaches multi-nC level for current femtosecond lasers, that is not available for standard wakefield-based accelerators with relatively low gas density as well as for electron acceleration from planar solid targets with step-like density profile.
Our findings constitute an important approach to laser-based radiation and radioactive sources for enhanced multi-keV x-ray betatron source, deep gamma-radiography of dense samples, neutron generation, positrons and mesons production. This approach is demonstrated on some examples for multi-TW and 1 PW lasers.
This work was supported by the Russian Science Foundation (Grant No. 17-12-01283).
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