On the Specific Features of Temperature Evolution in Ultracold Plasmas

TL;DR

This paper provides a theoretical explanation for the observed slow decay of temperature in ultracold plasmas, attributing it to the specific equation of state and Coulomb interactions, supported by analytical and numerical methods.

Contribution

It introduces a model explaining the temperature evolution in ultracold plasmas with strong Coulomb coupling, contrasting with classical gas expansion expectations.

Findings

Temperature decay follows T_e ~ t^{-(1.2 +/- 0.1)} instead of t^{-2}

Decelerated decay explained by the plasma's equation of state and Coulomb interactions

Numerical simulations confirm the analytical model and rapid approach to the asymptotic law

Abstract

A theoretical interpretation of the recent experimental studies of temperature evolution in the course of time in the freely-expanding ultracold plasma bunches, released from a magneto-optical trap, is discussed. The most interesting result is finding the asymptotics of the form T_e ~ t^{-(1.2 +/- 0.1)} instead of t^{-2}, which was expected for the rarefied monatomic gas during inertial expansion. As follows from our consideration, the substantially decelerated decay of the temperature can be well explained by the specific features of the equation of state for the ultracold plasmas with strong Coulomb's coupling, whereas a heat release due to inelastic processes (in particular, three-body recombination) does not play an appreciable role in the first approximation. This conclusion is confirmed both by approximate analytical estimates, based on the model of "virialization" of the charged-particle energies, and by the results of "ab initio" numerical simulation. Moreover, the simulation shows that the above-mentioned law of temperature evolution is approached very quickly--when the virial criterion is satisfied only within a factor on the order of unity.