Proton stopping measurements at low velocity in warm dense carbon

Ion stopping in warm dense matter is a process of fundamental importance for the understanding of the properties of dense plasmas, the realization and the interpretation of experiments involving ion beam-induced warm dense matter samples, and for inertial confinement fusion research. The theoretical description of the ion stopping power in warm dense matter is difficult notably due to electron coupling and degeneracy, and measurements are still largely missing. In particular, the low-velocity stopping range around the Bragg peak, that features the largest modelling uncertainties, remains virtually unexplored. Here, we report proton energy-loss measurements in warm dense plasma at lower projectile velocities than previous experiments, coming significantly closer to the Bragg peak region. Our energy-loss data, combined with a precise target characterization based on plasma temperature measurements us-
ing two different diagnostics, demonstrate a significant deviation of the stopping power from classical models in this regime. In particular, we show
that our results are consistent with recent first-principles simulations based on time-dependent density functional theory.