arXiv subjects

Scott D. Baalrud

Publications and source records attributed to Scott D. Baalrud.

41 records · Page 3Linked to original sources

arXiv2014

Instability-Enhanced Friction in the Presheath of Two-Ion-Species Plasmas

The speed at which ions enter a sheath is a fundamental property of a plasma that also provides a useful boundary condition in modeling. A recent theory proposed that this can be significantly influenced by an instability-enhanced friction force arising from two-stream instabilities in the presheath when multiple ion species are present. Although experiments appeared to confirm this theory, recent particle simulations have brought it into question. We reconcile this controversy using direct numerical solutions of the dispersion relation, which show that there is a dependence on the electron-ion temperature ratio that was not considered previously. In addition, particle-in-cell simulations are used to show that ion-ion two-stream instabilities can arise near the sheath edge and generate an enhanced ion-ion friction force. Only by accounting for the instability-enhanced friction force can theory predict the simulated ion speeds at the sheath edge.

physics.plasm-ph↗

arXiv2014

Accurate Determination of the Shear Viscosity of the One-Component Plasma

The shear viscosity coefficient of the one-component plasma is calculated with unprecedented accuracy using equilibrium molecular dynamics simulations and the Green-Kubo relation. Numerical and statistical uncertainties and their mitigation for improving accuracy are analyzed. In the weakly coupled regime, our the results agree with the Landau-Spitzer prediction. In the moderately and strongly coupled regimes, our results are found in good agreement with recent results obtained for the Yukawa one-component plasma using non-equilibrium molecular dynamics. A practical formula is provided for evaluating the viscosity coefficient across coupling regimes, from the weakly-coupled regime up to solidification threshold. The results are used to test theoretical predictions of the viscosity coefficients found in the literature.

physics.plasm-ph↗

arXiv2013

An Effective Potential Theory for Transport Coefficients Across Coupling Regimes

A plasma transport theory that spans weak to strong coupling is developed from a binary collision picture, but where the interaction potential is taken to be an effective potential that includes correlation effects and screening self-consistently. This physically motivated approach provides a practical model for evaluating transport coefficients across coupling regimes. The theory is shown to compare well with classical molecular dynamics simulations of temperature relaxation in electron-ion plasmas, as well as simulations and experiments of self-diffusion in one component plasmas. The approach is versatile and can be applied to other transport coefficients as well.

physics.plasm-ph↗

arXiv2013

The incomplete plasma dispersion function: properties and application to waves in bounded plasmas

The incomplete plasma dispersion function is a generalization of the plasma dispersion function in which the defining integral spans a semi-infinite, rather than infinite, domain. It is useful for describing the linear dielectric response and wave dispersion in non-Maxwellian plasmas when the distribution functions can be approximated as Maxwellian over finite, or semi-infinite, intervals in velocity phase-space. A ubiquitous example is the depleted Maxwellian electron distribution found near boundary sheaths or double layers, where the passing interval can be modeled as Maxwellian with a lower temperature than the trapped interval. The depleted Maxwellian is used as an example to demonstrate the utility of using the incomplete plasma dispersion function for calculating modifications to wave dispersion relations.

physics.plasm-ph↗

arXiv2011

A generalized Coulomb logarithm for strongly coupled plasmas

Transport coefficients for Coulomb collision processes, e.g., friction, energy exchange, and resistivity, are calculated for Debye-screened (Yukawa) plasmas including correlation effects within the binary collision approximation. A generalized Coulomb logarithm, $Ξ(Λ)$, is required, which asymptotes to $\ln Λ$ in the weakly coupled limit, but is significantly modified when $Λ\lesssim 10^2$ due to large angle collisions. In the regime $10^{-2} \lesssim Λ\lesssim 10^2$, $Ξ$ can be substantially larger for attractive collisions than repulsive.

physics.plasm-ph↗