Electron Screening Effects in a Strongly Coupled Ultracold Neutral Plasma

We study equilibration of strongly coupled ions in an ultracold neutral plasma produced by photo-ionizing laser-cooled and trapped atoms. By varying the electron temperature, we show that electron screening modifies the equilibrium ion temperature. Even with few electrons in a Debye sphere, the screening is well described by a model using Yukawa ion-ion potential. We also observe damped oscillations of the ion kinetic energy that are a unique feature of equilibration of strongly coupled plasma.