Experimental measurement of non-Markovian dynamics and self-diffusion in a strongly coupled plasma

TL;DR

This paper experimentally investigates non-Markovian effects and self-diffusion in a strongly coupled ultracold plasma, revealing deviations from standard kinetic theory and providing new insights into plasma transport properties.

Contribution

It demonstrates the measurement of non-Markovian dynamics and calculates the ion self-diffusion constant in a strongly coupled plasma, linking experimental data to fundamental transport coefficients.

Findings

Non-exponential decay indicates non-Markovian behavior.

Average velocity curve equals the velocity autocorrelation function.

Calculated ion self-diffusion constant in strongly coupled plasma.

Abstract

We present a study of the collisional relaxation of ion velocities in a strongly coupled, ultracold neutral plasma on short timescales compared to the inverse collision rate. Non-exponential decay towards equilibrium for the average velocity of a tagged population of ions heralds non-Markovian dynamics and a breakdown of assumptions underlying standard kinetic theory. We prove the equivalence of the average-velocity curve to the velocity autocorrelation function, a fundamental statistical quantity that provides access to equilibrium transport coefficients and aspects of individual particle trajectories in a regime where experimental measurements have been lacking. From our data, we calculate the ion self-diffusion constant. This demonstrates the utility of ultracold neutral plasmas for isolating the effects of strong coupling on collisional processes, which is of interest for dense laboratory and astrophysical plasmas.