Solid-Density Ion Temperature from Redshifted and Double-Peaked Stark Line Shapes

B. F. Kraus, Lan Gao, K. W. Hill, M. Bitter, P. C. Efthimion, T. A. Gomez, A. Moreau, R. Hollinger, Shoujun Wang, Huanyu Song, J. J. Rocca, and R. C. Mancini
Phys. Rev. Lett. 127, 205001 – Published 12 November 2021
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Abstract

Heβ spectral line shapes are important for diagnosing temperature and density in many dense plasmas. This work presents Heβ line shapes measured with high spectral resolution from solid-density plasmas with minimized gradients. The line shapes show hallmark features of Stark broadening, including quantifiable redshifts and double-peaked structure with a significant dip between the peaks; these features are compared to models through a Markov chain Monte Carlo framework. Line shape theory using the dipole approximation can fit the width and peak separation of measured line shapes, but it cannot resolve an ambiguity between electron density ne and ion temperature Ti, since both parameters influence the strength of quasistatic ion microfields. Here a line shape model employing a full Coulomb interaction for the electron broadening computes self-consistent line widths and redshifts through the monopole term; redshifts have different dependence on plasma parameters and thus resolve the neTi ambiguity. The measured line shapes indicate densities that are 80–100% of solid, identifying a regime of highly ionized but well-tamped plasma. This analysis also provides the first strong evidence that dense ions and electrons are not in thermal equilibrium, despite equilibration times much shorter than the duration of x-ray emission; cooler ions may arise from nonclassical thermalization rates or anomalous energy transport. The experimental platform and diagnostic technique constitute a promising new approach for studying ion-electron equilibration in dense plasmas.

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  • Received 9 April 2021
  • Revised 27 August 2021
  • Accepted 1 October 2021

DOI:https://doi.org/10.1103/PhysRevLett.127.205001

© 2021 American Physical Society

Physics Subject Headings (PhySH)

Plasma Physics

Authors & Affiliations

B. F. Kraus1,2,*, Lan Gao2, K. W. Hill2, M. Bitter2, P. C. Efthimion2, T. A. Gomez3, A. Moreau4, R. Hollinger4, Shoujun Wang4, Huanyu Song4, J. J. Rocca4,5, and R. C. Mancini6

  • 1Department of Astrophysical Sciences, Princeton University, Princeton, New Jersey 08544, USA
  • 2Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543, USA
  • 3Sandia National Laboratory, Albuquerque, New Mexico 87123, USA
  • 4Electrical and Computer Engineering Department, Colorado State University, Fort Collins, Colorado 80523, USA
  • 5Physics Department, Colorado State University, Fort Collins, Colorado 80523, USA
  • 6Department of Physics, University of Nevada, Reno, Nevada 89557, USA

  • *Corresponding author. bkraus@pppl.gov

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Issue

Vol. 127, Iss. 20 — 12 November 2021

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