arXiv subjects

Jason M. TenBarge

Publications and source records attributed to Jason M. TenBarge.

23 records · Page 2Linked to original sources

arXiv2017

Diagnosing collisionless energy transfer using field-particle correlations: gyrokinetic turbulence

Determining the physical mechanisms that extract energy from turbulent fluctuations in weakly collisional magnetized plasmas is necessary for a more complete characterization of the behavior of a variety of space and astrophysical plasmas. Such a determination is complicated by the complex nature of the turbulence as well as observational constraints, chiefly that in situ measurements of such plasmas are typically only available at a single point in space. Recent work has shown that correlations between electric fields and particle velocity distributions constructed from single-point measurements produce a velocity-dependent signature of the collisionless damping mechanism. We extend this work by constructing field-particle correlations using data sets drawn from single points in strongly driven, turbulent, electromagnetic gyrokinetic simulations to demonstrate that this technique can identify the collisionless mechanisms operating in such systems. The correlation's velocity-space structure agrees with expectations of resonant mechanisms transferring energy collisionlessly in turbulent systems. This work motivates the eventual application of field-particle correlations to spacecraft measurements in the solar wind, with the ultimate goal to determine the physical mechanisms that dissipate magnetized plasma turbulence.

physics.plasm-ph↗

arXiv2016

Energy Dissipation and Landau Damping in Two- and Three-Dimensional Plasma Turbulence

Plasma turbulence is ubiquitous in space and astrophysical plasmas, playing an important role in plasma energization, but the physical mechanisms leading to dissipation of the turbulent energy remain to be definitively identified. Kinetic simulations in two dimensions (2D) have been extensively used to study the dissipation process. How the limitation to 2D affects energy dissipation remains unclear. This work provides a model of comparison between two- and three-dimensional (3D) plasma turbulence using gyrokinetic simulations; it also explores the dynamics of distribution functions during the dissipation process. It is found that both 2D and 3D nonlinear gyrokinetic simulations of a low-beta plasma generate electron velocity-space structures with the same characteristics as that of linear Landau damping of Alfvén waves in a 3D linear simulation. The continual occurrence of the velocity-space structures throughout the turbulence simulations suggests that the action of Landau damping may be responsible for the turbulent energy transfer to electrons in both 2D and 3D, and makes possible the subsequent irreversible heating of the plasma through collisional smoothing of the velocity-space fluctuations. Although, in the 2D case where variation along the equilibrium magnetic field is absent, it may be expected that Landau damping is not possible, a common trigonometric factor appears in the 2D resonant denominator, leaving the resonance condition unchanged from the 3D case. The evolution of the 2D and 3D cases is qualitatively similar. However, quantitatively the nonlinear energy cascade and subsequent dissipation is significantly slower in the 2D case.

astro-ph.SR↗

arXiv2014

The Quasilinear Premise for the Modeling of Plasma Turbulence

The quasilinear premise is a hypothesis for the modeling of plasma turbulence in which the turbulent fluctuations are represented by a superposition of randomly-phased linear wave modes, and energy is transferred among these wave modes via nonlinear interactions. We define specifically what constitutes the quasilinear premise, and present a range of theoretical arguments in support of the relevance of linear wave properties even in a strongly turbulent plasma. We review evidence both in support of and in conflict with the quasilinear premise from numerical simulations and measurements of plasma turbulence in the solar wind. Although the question of the validity of the quasilinear premise remains to be settled, we suggest that the evidence largely supports the value of the quasilinear premise in modeling plasma turbulence and that its usefulness may also be judged by the insights gained from such an approach, with the ultimate goal to develop the capability to predict the evolution of any turbulent plasma system, including the spectrum of turbulent fluctuations, their dissipation, and the resulting plasma heating.

astro-ph.SR↗

arXiv2014

Physical Interpretation of the Angle Dependent Magnetic Helicity Spectrum in the Solar Wind: The Nature of Turbulent Fluctuations near the Proton Gyroradius Scale

Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated by wave period and angle between the local magnetic field and the solar wind velocity, this paper undertakes a comparison of three intervals of \emph{Ulysses} data with synthetic time series generated from a physically motivated turbulence model. From these comparisons, it is hypothesized that the observed signatures result from a perpendicular cascade of \Alfvenic fluctuations and a local, non-turbulent population of ion cyclotron or whistler waves generated by temperature anisotropy instabilities. By constraining the model's free parameters through comparison to \emph{in situ} data, it is found that, on average, $ \sim 95\%$ of the power near dissipative scales is contained in a perpendicular \Alfvenic cascade and that the parallel fluctuations are propagating nearly unidirectionally. The effects of aliasing on magnetic helicity measurements are considered and shown to be significant near the Nyquist frequency.

physics.plasm-ph↗

arXiv2011

Gyrokinetic Simulations of Solar Wind Turbulence from Ion to Electron Scales

The first three-dimensional, nonlinear gyrokinetic simulation of plasma turbulence resolving scales from the ion to electron gyroradius with a realistic mass ratio is presented, where all damping is provided by resolved physical mechanisms. The resulting energy spectra are quantitatively consistent with a magnetic power spectrum scaling of $k^{-2.8}$ as observed in \emph{in situ} spacecraft measurements of the "dissipation range" of solar wind turbulence. Despite the strongly nonlinear nature of the turbulence, the linear kinetic \Alfven wave mode quantitatively describes the polarization of the turbulent fluctuations. The collisional ion heating is measured at sub-ion-Larmor radius scales, which provides the first evidence of the ion entropy cascade in an electromagnetic turbulence simulation.

astro-ph.SR↗