Proton radiography is a useful diagnostic of high energy density (HED) plasmas under active theoretical and experimental development. In this paper we describe a new simulation tool that interacts realistic laser-driven point-like proton sources with
three dimensional electromagnetic fields of arbitrary strength and structure and synthesizes the associated high resolution proton radiograph. The present tools numerical approach captures all relevant physics effects, including effects related to the formation of caustics. Electromagnetic fields can be imported from PIC or hydrodynamic codes in a streamlined fashion, and a library of electromagnetic field `primitives is also provided. This latter capability allows users to add a primitive, modify the field strength, rotate a primitive, and so on, while quickly generating a high resolution radiograph at each step. In this way, our tool enables the user to deconstruct features in a radiograph and interpret them in connection to specific underlying electromagnetic field elements. We show an example application of the tool in connection to experimental observations of the Weibel instability in counterstreaming plasmas, using $sim 10^8$ particles generated from a realistic laser-driven point-like proton source, imaging fields which cover volumes of $sim10 $ mm$^3$. Insights derived from this application show that the tool can support understanding of HED plasmas.
We derive upper and lower bounds on the absorption of ultraintense laser light by solids as a function of fundamental laser and plasma parameters. These limits emerge naturally from constrained optimization techniques applied to a generalization of t
he laser-solid interaction as a strongly-driven, relativistic, two degree of freedom Maxwell-Vlasov system. We demonstrate that the extrema and the phase-space-averaged absorption must always increase with intensity, and increase most rapidly when $10^{18} < I_L lambda_L^2 < 10^{20}$ W $mu$m$^2/$cm$^{2}$. Our results indicate that the fundamental empirical trend towards increasing fractional absorption with irradiance therefore reflects the underlying phase space constraints.
Two dimensional particle-in-cell simulations characterizing the interaction of ultraintense short pulse lasers in the range 10^{18} leq I leq 10^{20} W/cm^{2} with converging target geometries are presented. Seeking to examine intensity amplification
in high-power laser systems, where focal spots are typically non-diffraction limited, we describe key dynamical features as the injected laser intensity and convergence angle of the target are systematically varied. We find that laser pulses are focused down to a wavelength with the peak intensity amplified by an order of magnitude beyond its vacuum value, and develop a simple model for how the peak location moves back towards the injection plane over time. This performance is sustained over hundreds of femtoseconds and scales to laser intensities beyond 10^{20} W/cm^{2} at 1 mu m wavelength.
