Extreme magnetic field generation in ultra-intense laser solid interactions

In the interaction of ultra-intense laser pulses (>10²³ W/cm²) with solid targets it is expected that 0.1 MT magnetic fields may be generated, potentially allowing for the experimental study of important collective processes in extreme astrophysical plasmas. At these extreme laser intensities a significant fraction of the pulse energy may be converted to high-energy radiation or electron-positron pairs, potentially limiting magnetic field generation. Using the quantum electrodynamic (QED) module in the OSIRIS particle-in-cell code, we perform a series of 2D simulations to study the generation of target-surface magnetic fields. These simulations are performed from a₀ = 50 to 500, allowing us to determine a scaling of the resulting magnetic field strength with laser intensity. The emission of high-energy photons is found to limit field generation, with almost 40% of the total laser energy being converted to radiation at a₀ = 500. An analytical model is developed allowing for the estimation of the maximum strength of magnetic fields on the target surface using laser parameters.