Experimental Measurement of Refilling Rates in the High-Energy Tail of the Thermal Electron Distribution of Ultracold Neutral Plasmas

Plasma electrons and ions in the high-energy tails of velocity distributions are of interest because of their importance in fusion, Tokamak, runaway electron, and fundamental physics research. Ultracold neutral plasmas (UNPs) can be studied in controlled table-top conditions, providing an experimental setting for studying the behavior of the rate at which electrons populate the high-energy tail of their velocity distribution. Measured rates can be used to test theoretical descriptions that are applicable not only to electrons but other particles in the plasma. We have developed an applied electric field sequence that depletes and then measures the refill rate of electrons in the high-energy tail of the velocity distribution without experimental distortions that were previously present. We can model the UNP electron extraction and fill rates using a Molecular Dynamics (MD) code to convert our measured data to quantities that can be compared to theory predictions. Measured refill rates along with descriptions of the experimental challenges will be presented.