Ion friction at small values of the Coulomb logarithm

Tucker Sprenkle, Adam Dodson, Quinton McKnight, Ross Spencer, Scott Bergeson, Abdourahmane Diaw, Michael S. Murillo

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

Transport properties of high-energy-density plasmas are influenced by the ion collision rate. Traditionally, this rate involves the Coulomb logarithm, lnΛ. Typical values of lnΛ are ≈10-20 in kinetic theories where transport properties are dominated by weak-scattering events caused by long-range forces. The validity of these theories breaks down for strongly coupled plasmas, when lnΛ is of order one. We present measurements and simulations of collision data in strongly coupled plasmas when lnΛ is small. Experiments are carried out in the first dual-species ultracold neutral plasma (UNP), using Ca+ and Yb+ ions. We find strong collisional coupling between the different ion species in the bulk of the plasma. We simulate the plasma using a two-species fluid code that includes Coulomb logarithms derived from either a screened Coulomb potential or a the potential of mean force. We find generally good agreement between the experimental measurements and the simulations. With some improvements, the mixed Ca+ and Yb+ dual-species UNP will be a promising platform for testing theoretical expressions for lnΛ and collision cross-sections from kinetic theories through measurements of energy relaxation, stopping power, two-stream instabilities, and the evolution of sculpted distribution functions in an idealized environment in which the initial temperatures, densities, and charge states are accurately known.

Original languageEnglish
Article number053206
JournalPhysical Review E - Statistical, Nonlinear, and Soft Matter Physics
Volume99
Issue number5
DOIs
StatePublished - May 21 2019
Externally publishedYes

Funding

This project was supported by grants from the National Science Foundation (Grant No. PHY-1500376) and the Air Force Office of Scientific Research (Grant No. AFOSR FA9550-17-1-0302). The authors express appreciation to Scott Baalrud and Jerome Daligault for helpful discussions concerning the effective potential approach.

FundersFunder number
National Science Foundation1500376, PHY-1500376
Air Force Office of Scientific Research

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