A status update on MIT's studies of ion-stopping power in Warm Dense Matter (WDM) plasmas

A platform has been developed and extensively used to accurately measure ion-stopping power in Warm Dense Matter (WDM) plasmas at conditions characterized by x-ray Thomson scattering at the OMEGA. A cylindrical geometry has been used to allow charged-particle be transported along the symmetry axis of the WDM plasma. Either a solid-density beryllium, boron or carbon cylinder was isochorically heated by L-shell x-ray emission generated on the outside of the cylinder to temperatures up to about 30 eV, corresponding to moderately-coupled (Γ ~ 0.3) and moderately-degenerate (θ ~ 2) WDM conditions. The results from these experiments illustrate an increase energy loss in WDM relative to cold matter, consistent with a reduced mean ionization potential, which is well-described by ion-stopping-power models based on an ad-hoc treatment of free and bound electrons, as well as the average-atom local-density approximation. With this experimental platform, the insignificance of electromagnetic fields around the target was demonstrated. Going forward, the plan is to build on these results and use lower-velocity ions for studies of WDM ion-stopping power closer to the Bragg peak.