Simulations and Experimental Measurement of Refilling Rates in the High-Energy Tail of the Thermal Electron Distribution of Ultra Cold Plasmas*

Plasma electrons and ions in the high-energy tails of velocity distributions are of interest because of their importance in fusion, Tokamak, and fundamental physics research. Fusion collisions are largely between the highest-energy ions because of how their cross-section scales with energy. Runaway electrons that are of concern in fusion and Tokamak research originate from the tails of the distribution. Ultra cold plasmas (UCPs) can be studied in controlled table-top conditions, providing an excellent 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. By applying electric field sequences to a UCP, we can deplete and then measure the refill rate of electrons in the high-energy tail of the velocity distribution. We can model the electric field sequences using Molecular Dynamics (MD) code to determine the optimal waveforms and timing sequences needed to avoid losing energy within the system and observe refill rates. Analysis from MD simulations and preliminary data measuring the refill rates along with descriptions of the experimental challenges will be presented.