Ion temperature evolution in an ultracold neutral plasma

McQuillen, Patrick; Strickler, Trevor; Langin, Thomas; Killian, T. C.

doi:10.1063/1.4915135

Cited by 31 publications

(39 citation statements)

References 88 publications

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“…On the long timescale of temperature relaxation, UNPs are subject to other heating and cooling mechanisms (especially three-body recombination heating) that obscure the electron-ion collision physics. 24 Velocity relaxation, however, is faster than temperature relaxation by a factor of about m i /m e . This makes it a suitable probe of electron-ion collisional transport (and thus the Barkas effect), since a drift velocity can relax on a timescale that is short compared to both temperature relaxation and three-body recombination.…”

Section: Molecular Dynamics Simulationsmentioning

confidence: 96%

The Barkas effect in plasma transport

Shaffer

2019

Physics of Plasmas

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Molecular dynamics simulations reveal that a fundamental symmetry of plasma kinetic theory is broken at moderate to strong Coulomb coupling: the collision rate depends on the signs of the colliding charges. This symmetry breaking is analogous to the Barkas effect observed in charged-particle stopping experiments and gives rise to significantly enhanced electron-ion collision rates. It is expected to affect any neutral plasma with moderate to strong Coulomb coupling such as ultracold neutral plasmas (UNP) and the dense plasmas of ICF and laser-matter interaction experiments.

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Section: Molecular Dynamics Simulationsmentioning

confidence: 96%

The Barkas effect in plasma transport

Shaffer

2019

Physics of Plasmas

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“…Measurements of the velocity autocorrelation function and the self-diffusion constant are performed after the DIH is complete and the plasma is near local thermal equilibrium. After DIH, the ion temperature still changes due to electron-ion heating and cooling from expansion into the vacuum [56], but this is a slow evolution compared to the experimental time scale.…”

Section: Appendix B: Variation and Uncertainties Of Plasma Parametersmentioning

confidence: 99%

Experimental Measurement of Self-Diffusion in a Strongly Coupled Plasma

et al. 2016

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We present a study of the collisional relaxation of ion velocities in a strongly coupled, ultracold neutral plasma on short time scales compared to the inverse collision rate. The measured average velocity of a tagged population of ions is shown to be equivalent to the ion-velocity autocorrelation function. We thus gain access to fundamental aspects of the single-particle dynamics in strongly coupled plasmas and to the ion self-diffusion constant under conditions where experimental measurements have been lacking. Nonexponential decay towards equilibrium of the average velocity heralds non-Markovian dynamics that are not predicted by traditional descriptions of weakly coupled plasmas. This demonstrates the utility of ultracold neutral plasmas for studying the effects of strong coupling on collisional processes, which is of interest for dense laboratory and astrophysical plasmas.

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“…For example, one can imagine an experiment in which the Ca plasma is generated and allowed to expand. As it expands, the ion-ion coupling parameter increases to values near 5 [56]. The co-located Yb plasma could then be generated and the interaction between the cold Ca + ions and the hot Yb + ions could be measured.…”

Section: Discussionmentioning

confidence: 99%

“…Consistent with Ref. [56] and many other UNP studies, we take the ion strong coupling parameter to be,…”

Section: A the Coulomb Logarithm And Momentum Transfermentioning

confidence: 99%

“…Simulations [43,44], laser spectroscopy [30,45,46], radio-frequency measurements [47,48], charged particle detection and imaging [49,50] are all used to characterize these systems. They have deepened our understanding of the time-evolving density [51,52], electron and ion temperatures [48,[53][54][55][56][57], collision and recombination rates [58,59], expansion, velocity relaxation [30], localization [60], and self-diffusion [28] in strongly-coupled Coulomb systems. The recent realization of laser-cooling ions in an ultracold neutral plasma open the possibility of extending all of these studies farther into the strongly coupled plasma regime [61].…”

Section: Introductionmentioning

confidence: 99%

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Ion friction at small values of the Coulomb logarithm

et al. 2019

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Transport properties of high-energy-density plasmas are influenced by the ion collision rate. Traditionally, this rate involves the Coulomb logarithm, ln Λ. Typical values of ln Λ are ≈ 10 to 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 ln Λ is of order one. We present measurements and simulations of collision data in strongly-coupled plasmas when ln Λ 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 ln Λ 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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Ion temperature evolution in an ultracold neutral plasma

Cited by 31 publications

References 88 publications

The Barkas effect in plasma transport

The Barkas effect in plasma transport

Experimental Measurement of Self-Diffusion in a Strongly Coupled Plasma

Ion friction at small values of the Coulomb logarithm

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