Energy relaxation in a Ca/Yb dual-species ultracold neutral plasma

We report relaxation measurements in a Ca⁺/Yb⁺ dual species ultracold neutral plasma. The nearly 4:1 mass ratio of the ion species in our plasma is similar to the alpha:proton mass ratio important for fusion-class systems. Our system provides a platform for using Ca⁺ and Yb⁺ ions to find the Coulomb logarithm for momentum transfer collisions in a strongly coupled plasma environment. The velocity distributions are determined using laser-induced fluorescence. Measurements are compared to PIC code calculations that include ion friction and ambipolar field acceleration to describe dual species plasma expansion. We determine the Coulomb logarithm by comparing experimental data with the PIC results, and find Λ=0.04.