Measurements of Temperature Evolution in Copper from Intense Proton Beam Energy Deposition

Laser-driven intense proton beams provide short bunch duration and high rates of energy deposition optimal for laboratory studies in the Warm Dense Matter (WDM) regime. In the WDM regime, time-resolved X-ray spectroscopy can characterize samples during heating, yet this has largely remained unexplored in proton-heating experiments. We present an analysis of the first time-resolved K_α spectroscopy measurements from copper heated by an intense proton beam, using the High-Resolution streaked X-ray Spectrometer (HiResSpec) at OMEGA-EP. The EP short pulse laser (450-900 J, 5-10 ps) was focused onto a cone-enclosed partial hemisphere to generate and focus an intense proton beam onto a 10 μm- or 25 μm-thick solid copper sample. HiResSpec diagnoses the Cu k_α1 and k_α2 line emissions with a time resolution of a few picoseconds, allowing us to resolve temperature-dependent shifts of the lines; these correspond to sample temperatures up to ∼50 eV within ∼35 ps, according to atomic kinetics simulations. We compare these results to hybrid-PIC simulations and find consistent temperature evolution, when accounting for the temporal spreading of the proton beam as it traverses the cone. These measurements are an important contribution to the high-quality characterization required for benchmarking theoretical models in the WDM regime.