Ion friction at small values of the Coulomb logarithm

Tucker Sprenkle, Adam Dodson, Emma McKnight, Ross Spencer, Scott Bergeson, Abdourahmane Diaw, and Michael S. Murillo
Phys. Rev. E 99, 053206 – Published 21 May 2019

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 1020 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.

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  • Received 30 March 2018
  • Revised 15 November 2018

DOI:https://doi.org/10.1103/PhysRevE.99.053206

©2019 American Physical Society

Physics Subject Headings (PhySH)

Plasma PhysicsAtomic, Molecular & Optical

Authors & Affiliations

Tucker Sprenkle1, Adam Dodson1,*, Emma McKnight1, Ross Spencer1, Scott Bergeson1,†, Abdourahmane Diaw2,‡, and Michael S. Murillo3,§

  • 1Department of Physics and Astronomy, Brigham Young University, Provo, Utah 84602, USA
  • 2Computational Physics and Methods Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA
  • 3Department of Computational Mathematics, Science and Engineering, Michigan State University, East Lansing, Michigan 48824, USA

  • *Present address: Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA.
  • scott.bergeson@byu.edu
  • diaw@lanl.gov
  • §murillom@msu.edu

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Issue

Vol. 99, Iss. 5 — May 2019

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