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Title: Ion species stratification within strong shocks in two-ion plasmas

 [1]; ORCiD logo [1]; ORCiD logo [1];  [1]
  1. Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
Publication Date:
Sponsoring Org.:
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Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 3; Related Information: CHORUS Timestamp: 2018-03-01 15:12:36; Journal ID: ISSN 1070-664X
American Institute of Physics
Country of Publication:
United States

Citation Formats

Keenan, Brett D., Simakov, Andrei N., Taitano, William T., and Chacón, Luis. Ion species stratification within strong shocks in two-ion plasmas. United States: N. p., 2018. Web. doi:10.1063/1.5020156.
Keenan, Brett D., Simakov, Andrei N., Taitano, William T., & Chacón, Luis. Ion species stratification within strong shocks in two-ion plasmas. United States. doi:10.1063/1.5020156.
Keenan, Brett D., Simakov, Andrei N., Taitano, William T., and Chacón, Luis. 2018. "Ion species stratification within strong shocks in two-ion plasmas". United States. doi:10.1063/1.5020156.
title = {Ion species stratification within strong shocks in two-ion plasmas},
author = {Keenan, Brett D. and Simakov, Andrei N. and Taitano, William T. and Chacón, Luis},
abstractNote = {},
doi = {10.1063/1.5020156},
journal = {Physics of Plasmas},
number = 3,
volume = 25,
place = {United States},
year = 2018,
month = 3

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on March 1, 2019
Publisher's Accepted Manuscript

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  • We report strong collisional shocks in multi-ion plasmas are featured in many environments, with Inertial Confinement Fusion (ICF) experiments being one prominent example. Recent work [Keenan et al., Phys. Rev. E 96, 053203 (2017)] answered in detail a number of outstanding questions concerning the kinetic structure of steady-state, planar plasma shocks, e.g., the shock width scaling by the Mach number, M. However, it did not discuss shock-driven ion-species stratification (e.g., relative concentration modification and temperature separation). These are important effects since many recent ICF experiments have evaded explanation by standard, single-fluid, radiation-hydrodynamic (rad-hydro) numerical simulations, and shock-driven fuel stratification likelymore » contributes to this discrepancy. Employing the state-of-the-art Vlasov-Fokker-Planck code, iFP, along with multi-ion hydro simulations and semi-analytics, we quantify the ion stratification by planar shocks with the arbitrary Mach number and the relative species concentration for two-ion plasmas in terms of ion mass and charge ratios. In particular, for strong shocks, we find that the structure of the ion temperature separation has a nearly universal character across ion mass and charge ratios. Lastly, we find that the shock fronts are enriched with the lighter ion species and the enrichment scales as M 4 for M»1.« less
  • Supernova remnant and heliopause termination shock plasmas may contain significant populations of minority heavy ions, with relative number densities n{sub α}/n{sub i} up to 50%. Preliminary kinetic simulations of collisionless shocks in these environments showed that the reformation cycle and acceleration mechanisms at quasi-perpendicular shocks can depend on the value of n{sub α}/n{sub i} . Shock reformation unfolds on ion spatio-temporal scales, requiring fully kinetic simulations of particle dynamics, together with the self-consistent electric and magnetic fields. This paper presents the first set of particle-in-cell simulations for two ion species, protons (n{sub p} ) and α-particles (n{sub α}), with differingmore » mass and charge-to-mass ratios, that spans the entire range of n{sub α}/n{sub i} from 0% to 100%. The interplay between the differing gyro length scales and timescales of the ion species is crucial to the time-evolving phenomenology of the shocks, the downstream turbulence, and the particle acceleration at different n{sub α}/n{sub i} . We show how the overall energization changes with n{sub α}/n{sub i} , and relate this to the processes individual ions undergo in the shock region and in the downstream turbulence, and to the power spectra of magnetic field fluctuations. The crossover between shocks dominated by the respective ion species happens when n{sub α}/n{sub i} = 25%, and minority ion energization is strongest in this regime. Energization of the majority ion species scales with injection energy. The power spectrum of the downstream turbulence includes peaks at sequential ion cyclotron harmonics, suggestive of ion ring-beam collective instability.« less
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  • We derive fluid equations for describing steady-state planar shocks of a moderate strength (0 < M - 1 ≲ 1 with M the shock Mach number) propagating through an unmagnetized quasineutral collisional plasma comprising two separate ion species. In addition to the standard fluid shock quantities, such as the total mass density, mass-flow velocity, and electron and average ion temperatures, the equations describe shock stratification in terms of variations in the relative concentrations and temperatures of the two ion species along the shock propagation direction. We have solved these equations analytically for weak shocks (0 < M - 1 <<more » 1), with the results depending on M, ratios of the ion masses and charges, and the upstream mass fraction of one of the ion species. These analytical results are instrumental for gaining understanding in the behavior of weak shocks, and they have been used to verify kinetic simulations of shocks in multi-ion plasmas.« less
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  • Free convection over a vertical flat plate embedded in a thermally stratified porous medium is analyzed by exploiting the similarity transformation procedure. Numerical integration results are presented for a series of wall and ambient temperature distributions which permit similarity solutions. The conjugate conduction connection problems of a free convection fin embedded in a thermally stratified porous medium is examined, and it is shown that the influence of the thermal stratification on the heat transfer is quite significant. 8 references.