On the quasi-linear diffusion in collisionless plasmas (to say nothing about Landau damping)

2012 ◽  
Vol 19 (6) ◽  
pp. 062307 ◽  
Author(s):  
Petr Hellinger ◽  
Pavel M. Trávníček
Keyword(s):  
Landau Damping ◽  
Linear Diffusion ◽  
Collisionless Plasmas

scholarly journals Landau damping in one dimensional periodic inhomogeneous collisionless plasmas

AIP Advances ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 025229
Author(s):  
Sanjeev Kumar Pandey ◽  
Rajaraman Ganesh
Keyword(s):  
Landau Damping ◽  
One Dimensional ◽  
Collisionless Plasmas

scholarly journals Fluidization of collisionless plasma turbulence

2019 ◽  
Vol 116 (4) ◽  
pp. 1185-1194 ◽  
Author(s):  
Romain Meyrand ◽  
Anjor Kanekar ◽  
William Dorland ◽  
Alexander A. Schekochihin
Keyword(s):  
Solar Wind ◽  
Power Law ◽  
Collisionless Plasma ◽  
Plasma Turbulence ◽  
Magnetized Plasma ◽  
Landau Damping ◽  
Astrophysical Plasmas ◽  
Phase Mixing ◽  
Fluid Turbulence ◽  
Collisionless Plasmas

In a collisionless, magnetized plasma, particles may stream freely along magnetic field lines, leading to “phase mixing” of their distribution function and consequently, to smoothing out of any “compressive” fluctuations (of density, pressure, etc.). This rapid mixing underlies Landau damping of these fluctuations in a quiescent plasma—one of the most fundamental physical phenomena that makes plasma different from a conventional fluid. Nevertheless, broad power law spectra of compressive fluctuations are observed in turbulent astrophysical plasmas (most vividly, in the solar wind) under conditions conducive to strong Landau damping. Elsewhere in nature, such spectra are normally associated with fluid turbulence, where energy cannot be dissipated in the inertial-scale range and is, therefore, cascaded from large scales to small. By direct numerical simulations and theoretical arguments, it is shown here that turbulence of compressive fluctuations in collisionless plasmas strongly resembles one in a collisional fluid and does have broad power law spectra. This “fluidization” of collisionless plasmas occurs, because phase mixing is strongly suppressed on average by “stochastic echoes,” arising due to nonlinear advection of the particle distribution by turbulent motions. Other than resolving the long-standing puzzle of observed compressive fluctuations in the solar wind, our results suggest a conceptual shift for understanding kinetic plasma turbulence generally: rather than being a system where Landau damping plays the role of dissipation, a collisionless plasma is effectively dissipationless, except at very small scales. The universality of “fluid” turbulence physics is thus reaffirmed even for a kinetic, collisionless system.

scholarly journals Fluid simulations of non-resonant anisotropic ion heating

2013 ◽  
Vol 31 (7) ◽  
pp. 1195-1204 ◽  
Author(s):  
D. Laveder ◽  
T. Passot ◽  
P. L. Sulem
Keyword(s):  
Fluid Model ◽  
Dominant Role ◽  
Heat Fluxes ◽  
Landau Damping ◽  
Larmor Radius ◽  
Ion Heating ◽  
Thermal Dynamics ◽  
Dominant Type ◽  
Finite Larmor Radius ◽  
Collisionless Plasmas

Abstract. The finite Larmor radius (FLR)-Landau fluid model, which extends the usual anisotropic magnetohydrodynamics to magnetized collisionless plasmas by retaining linear Landau damping and finite Larmor radius corrections down to the sub-ionic scales in the quasi-transverse directions, is used to study the non-resonant heating of the plasma by randomly driven Alfvén waves. One-dimensional numerical simulations, free from any artificial dissipation, are used to analyze the influence on the thermal dynamics, of the beta parameter and of the separation between the driving and the ion scales. While the gyrotropic heat fluxes play a dominant role when the plasma is driven at large scales, leading to a parallel heating of the ions by Landau damping, a different regime develops when the driving acts at scales comparable to the ion Larmor radius. Perpendicular heating and parallel cooling of the ions are then observed, an effect that is mostly due to the work of the non-gyrotropic pressure force and that can be viewed as the fluid signature of the so-called stochastic heating. A partial characterization of the plasma by global quantities (such as the magnetic compressibility and the density-magnetic field correlations that provide information on the dominant type of waves) is also presented. The enhancement of the parallel electron heating by a higher level of fast magnetosonic waves is in particular pointed out.

Adaptive Multi-Physics Simulations of Collisionless Plasmas

2021 ◽  
Author(s):  
Simon Lautenbach ◽  
Rainer Grauer
Keyword(s):  
Magnetic Reconnection ◽  
Vlasov Equation ◽  
Fluid Model ◽  
Environmental Modeling ◽  
Landau Damping ◽  
Proof Of Concept ◽  
Collisionless Plasmas ◽  
Space Environments ◽  
Small Parts ◽  
Kinetic Treatment

<p>Collisionless plasmas, mostly present in astrophysical and space environments, often require a kinetic treatment given by the Vlasov equation. Unfortunately, the six-dimensional Vlasov equation is inherently expensive to compute and usually can only be solved on very small parts of the considered spatial domain. However, in some cases, e.g. magnetic reconnection, it is sufficient to solve the Vlasov equation in a localized domain and solve the remaining domain with appropriate fluid models. We present an adaptive hierarchical treatment of collisionless plasmas ranging from fully kinetic, to a 10-moment fluid model incorporating a simplified treatment of Landau damping, to a 5-moment fluid description. To account for separation of electron and ion physics, hybrid stages of mixed electron and ion models are also allowed. As a proof of concept, the full physics-adaptive hierarchy is applied to the Geospace Environmental Modeling (GEM) challenge of magnetic reconnection.</p>

scholarly journals Ergodic control of diffusions with random intervention times

2021 ◽  
Vol 58 (1) ◽  
pp. 1-21
Author(s):  
Harto Saarinen ◽  
Jukka Lempa
Keyword(s):  
Optimal Solution ◽  
Singular Control ◽  
Control Policy ◽  
Control Problems ◽  
Ergodic Control ◽  
Linear Diffusion ◽  
One Dimensional ◽  
And Diffusion ◽  
Independent Poisson Process ◽  
Exact Amount

AbstractWe study an ergodic singular control problem with constraint of a regular one-dimensional linear diffusion. The constraint allows the agent to control the diffusion only at the jump times of an independent Poisson process. Under relatively weak assumptions, we characterize the optimal solution as an impulse-type control policy, where it is optimal to exert the exact amount of control needed to push the process to a unique threshold. Moreover, we discuss the connection of the present problem to ergodic singular control problems, and illustrate the results with different well-known cost and diffusion structures.

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