The Alfvénic nature of energy transfer mediation in localized, strongly nonlinear Alfvén wavepacket collisions

Verniero, J. L.; Howes, G. G.

doi:10.1017/s0022377818000090

Cited by 12 publications

(15 citation statements)

References 42 publications

(114 reference statements)

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“…2013) has shown that a nonlinearly generated mode, which is not a solution of the linear dispersion relation, serves to mediate the energy transfer to small perpendicular scales. Future work will address the question of whether this nonlinearly generated mode still plays a key role in the more realistic case of localized Alfvén wavepacket collisions (Verniero & Howes 2018).…”

Section: Resultsmentioning

confidence: 99%

“…This is the transfer of energy to smaller perpendicular scales, illustrated by the plots of perpendicular magnetic energy in Fourier space in figure 4. A more quantitative examination contrasting the nonlinear transfer of energy between the idealized plane Alfvén wave collisions in a periodic geometry and localized Alfvén wavepackets collisions, in both the weakly and strongly nonlinear limits, will be presented in a subsequent paper (Verniero & Howes 2018).…”

Section: Evolution Of the Nonlinear Interactionmentioning

confidence: 99%

“…; and (ii) do Alfvén wavepacket collisions in the strongly nonlinear limit still lead to the development of intermittent current sheets? A companion paper (Verniero & Howes 2018) will investigate whether the nonlinearly generated mode still mediates the energy transfer in the weakly collisional limit of Alfvén wavepacket collisions.…”

Section: Introductionmentioning

confidence: 99%

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Nonlinear energy transfer and current sheet development in localized Alfvén wavepacket collisions in the strong turbulence limit

2018

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In space and astrophysical plasmas, turbulence is responsible for transferring energy from large scales driven by violent events or instabilities, to smaller scales where turbulent energy is ultimately converted into plasma heat by dissipative mechanisms. The nonlinear interaction between counterpropagating Alfvén waves, denoted Alfvén wave collisions, drives this turbulent energy cascade, as recognized by early work with incompressible magnetohydrodynamic (MHD) equations. Recent work employing analytical calculations and nonlinear gyrokinetic simulations of Alfvén wave collisions in an idealized periodic initial state have demonstrated the key properties that strong Alfvén wave collisions mediate effectively the transfer of energy to smaller perpendicular scales and self-consistently generate current sheets. For the more realistic case of the collision between two initially separated Alfvén wavepackets, we use a nonlinear gyrokinetic simulation to show here that these key properties persist: strong Alfvén wavepacket collisions indeed facilitate the perpendicular cascade of energy and give rise to current sheets. Furthermore, the evolution shows that nonlinear interactions occur only while the wavepackets overlap, followed by a clean separation of the wavepackets with straight uniform magnetic fields and the cessation of nonlinear evolution in between collisions, even in the gyrokinetic simulation presented here which resolves dispersive and kinetic effects beyond the reach of the MHD theory.

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Section: Resultsmentioning

confidence: 99%

Section: Evolution Of the Nonlinear Interactionmentioning

confidence: 99%

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Nonlinear energy transfer and current sheet development in localized Alfvén wavepacket collisions in the strong turbulence limit

2018

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“…Note that the two Alfvén waves are already overlapping at the beginning of this simulation before the nonlinear evolution begins, an idealized case which facilitates the comparison to an asymptotic analytical solution in the weakly nonlinear limit (Howes & Nielson 2013; Howes 2016). The nonlinear evolution of the development of current sheets is found to persist in the more realistic case of collisions between two initially separated Alfvén wavepackets of finite parallel extent (Verniero & Howes 2017; Verniero et al. 2018).…”

Section: Simulationmentioning

confidence: 99%

Spatially localized particle energization by Landau damping in current sheets produced by strong Alfvén wave collisions

2018

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Understanding the removal of energy from turbulent fluctuations in a magnetized plasma and the consequent energization of the constituent plasma particles is a major goal of heliophysics and astrophysics. Previous work has shown that nonlinear interactions among counterpropagating Alfvén waves – or Alfvén wave collisions – are the fundamental building block of astrophysical plasma turbulence and naturally generate current sheets in the strongly nonlinear limit. A nonlinear gyrokinetic simulation of a strong Alfvén wave collision is used to examine the damping of the electromagnetic fluctuations and the associated energization of particles that occurs in self-consistently generated current sheets. A simple model explains the flow of energy due to the collisionless damping and the associated particle energization, as well as the subsequent thermalization of the particle energy by collisions. The net particle energization by the parallel electric field is shown to be spatially localized, and the nonlinear evolution is essential in enabling spatial non-uniformity. Using the recently developed field–particle correlation technique, we show that particles resonant with the Alfvén waves in the simulation dominate the energy transfer, demonstrating conclusively that Landau damping plays a key role in the spatially localized damping of the electromagnetic fluctuations and consequent energization of the particles in this strongly nonlinear simulation.

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“…The success of this experimental investigation of Alfvén wave collisions has laid the foundation for subsequent advances in our theoretical understanding of how current sheets arise self-consistently in plasma turbulence, 70,124 the role played by resonant wave-particle interactions in the dissipation of these current sheets, 72 and how collisions between localized Alfvén wavepackets in the strongly nonlinear limit mediate the turbulent cascade of energy to small scales. 125,126 Observations of enhanced perpendicular ion temperatures in the solar corona 127 have lead to the important question of how ions are energized perpendicular to the magnetic field under low plasma beta conditions. Under similar low plasma beta and weakly collisional conditions, a broadband spectrum of anisotropic magnetic turbulence has been observed to arise during magnetic relaxation events in the Madison Symmetric Torus (MST ) experiment; 128 application of a Rutherford scattering diagnostic 129 has shown there to be anomalous ion heating coincident with this turbulence.…”

Section: A Plasma Turbulencementioning

confidence: 99%

Laboratory space physics: Investigating the physics of space plasmas in the laboratory

Howes

2018

Physics of Plasmas

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Laboratory experiments provide a valuable complement to explore the fundamental physics of space plasmas without the limitations inherent to spacecraft measurements. Specifically, experiments overcome the restriction that spacecraft measurements are made at only one (or a few) points in space, enable greater control of the plasma conditions and applied perturbations, can be reproducible, and are orders of magnitude less expensive than launching spacecraft. Here I highlight key open questions about the physics of space plasmas and identify the aspects of these problems that can potentially be tackled in laboratory experiments. Several past successes in laboratory space physics provide concrete examples of how complementary experiments can contribute to our understanding of physical processes at play in the solar corona, solar wind, planetary magnetospheres, and outer boundary of the heliosphere. I present developments on the horizon of laboratory space physics, identifying velocity space as a key new frontier, highlighting new and enhanced experimental facilities, and showcasing anticipated developments to produce improved diagnostics and innovative analysis methods. A strategy for future laboratory space physics investigations will be outlined, with explicit connections to specific fundamental plasma phenomena of interest.

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The Alfvénic nature of energy transfer mediation in localized, strongly nonlinear Alfvén wavepacket collisions

Cited by 12 publications

References 42 publications

Nonlinear energy transfer and current sheet development in localized Alfvén wavepacket collisions in the strong turbulence limit

Nonlinear energy transfer and current sheet development in localized Alfvén wavepacket collisions in the strong turbulence limit

Spatially localized particle energization by Landau damping in current sheets produced by strong Alfvén wave collisions

Laboratory space physics: Investigating the physics of space plasmas in the laboratory

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