Measurements of Proton Stopping Power in Warm Dense Matter approaching the Bragg Peak*

The transport of protons through plasma is a highly active field of research due to its myriad applications in high energy density science. A crucial accounting of proton transport is the energy loss rate dε/dx, or stopping power, that comes with propagation in some medium. In the gray space between condensed matter and plasma, warm dense matter (WDM) has proven to be one such perplexing medium, evading accurate modeling from both classical and quantum treatments. Models of proton stopping power in WDM generally agree for fast projectiles (v_p » v_th,e), but when compounded with the Bragg peak regime (v_p ≈ v_th,e) in which protons lose most of their energy quickly, model predictions vary by as much as 30-40%. The first experimental measurements of proton stopping power in WDM approaching the Bragg peak (v_p / v_th,e ~ 3-10) were made on the VEGA-II laser [1]. Here, we report on platform advancements made on the CSU ALEPH laser, where 500±10 keV protons with short bunch duration (<200 ps) were generated [2] and directed toward a laser-heated WDM sample. We present a preliminary analysis of the stopping power measurements along with WDM characterization through streaked optical pyrometry.

[1] S. Malko et al., Nature Communications 13.1 (2022): 2893.

[2] J. I. Apiñaniz et al., Scientific Reports 11.1 (2021): 6881.