Early time dynamics of strongly coupled ultracold neutral Ca and Ca plasmas

For interacting many-body systems the two most natural energy scales are the average energy per particle and the average nearest-neighbor potential energy. When the ratio of the nearest-neighbor potential energy to the kinetic energy is greater than 1, we say that the system is “strongly coupled,” where strong coupling is characterized by the parameter Γ. This dimensionless parameter describes the complete thermodynamic state of a system, making it possible to study the fundamental behavior of strongly coupled systems as manifested in high energy-density plasmas using low energy table-top experiments. In our experiments, we are working with plasmas in this exotic regime. In this paper we report on the progress of an experiment in laser-cooled calcium designed to increase the strong coupling of an ultracold neutral plasma by promoting the plasma ions to the second ionization state. We report preliminary measurements of the change in the Ca ion temperature due to the second ionization.