Universality in the Equilibration of Quenched Yukawa One Component Plasmas

We study the equilibration of a Yukawa One Component Plasma (OCP) after a rapid change in the screening parameter from $\kappa_{0}=\infty$ to $\kappa_{f}(n,T_{e})$, which is realized by photoionizing a laser cooled ($T\sim 10$\,mK), uncorrelated gas of $^{88}$Sr atoms with density $n$ between $10^{14}$\,m$^{-3}$ and $3\times10^{16}$\,m$^{-3}$ using a two photon process in which the energy of one of the photons is adjustable. The excess photon energy above the ionization threshold sets the electron temperature, $T_{e}$, and thus gives us control of $\kappa_{f}$. The resultant plasma is a classical plasma with strongly coupled ions, and is therefore described by the Yukawa OCP model with the electrons treated as a screening background. After photoionization, the ions develop spatial correlations to minimize their interaction energy, thus heating the ions. Since the dynamics of a Yukawa OCP depend solely on $\kappa$, we expect the heating process to be uniquely determined by $\kappa_{f}$. We verify this behavior by measuring the ion heating curve and comparing it to molecular dynamics simulations. We also report on how this behavior can be used to accurately measure $n$ given a measured equilibration curve at a known $T_{e}$.