Non-linear Alfvén wave interaction leading to resonant excitation of an acoustic mode in the laboratorya)

Dorfman, S.; Carter, Troy

doi:10.1063/1.4919275

Cited by 7 publications

(4 citation statements)

References 32 publications

(45 reference statements)

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“…Alfvén waves are also routinely launched in laboratory experiments at the LArge Plasma device (LAPD), which is a cylindrical device that produces a 16.5m-long column of quiescent, magnetized plasma 13 . Waves with various parameters can be launched using antennae placed at the ends of the column; there have been extensive experiments performed using LAPD on the linear [14][15][16][17] and nonlinear [18][19][20][21][22][23] properties of AW. The plasma regime in which these waves are launched may be similar to smallscale waves present in the solar corona and Earth's aurora:…”

Section: Introductionmentioning

confidence: 99%

Nonlinear dynamics of small-scale Alfvén waves

Mallet¹,

Dorfman²,

Abler³

et al. 2023

Preprint

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We study the nonlinear evolution of very oblique small-scale Alfvén waves with k ⊥ d i > ∼ 1. At these scales, the waves become significantly compressive, unlike in MHD, due to the Hall term in the equations. We demonstrate that when frequencies are small compared to the ion gyrofrequency and amplitudes small compared to unity, no new nonlinear interaction appears due to the Hall term alone at the lowest non-trivial order, even when k ⊥ d i ∼ 1. However, at the second non-trivial order, we discover that the Hall physics leads to a slow but resonant nonlinear interaction between co-propagating Alfvén waves, an inherently 3D effect. Including the effects of finite temperature, finite frequency, and electron inertia, the two-fluid Alfvén wave also becomes dispersive once one or more of k ⊥ ρ s , k ⊥ d e , or k d i becomes significant: for oblique waves at low β as studied here, this can be at a much smaller scale than d i . We show that the timescale for one-dimensional steepening of two-fluid Alfven waves is only significant at these smaller dispersive scales, and also derive an expression for the amplitude of driven harmonics of a primary wave. Importantly, both new effects are absent in gyrokinetics and other commonly used reduced two-fluid models. Our calculations have relevance for the interpretation of laboratory Alfvén wave experiments, as well as shedding light on the physics of turbulence in the solar corona and inner solar wind, where the dominant nonlinear interaction between counter-propagating waves is suppressed, allowing these new effects to become important.

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Section: Introductionmentioning

confidence: 99%

Nonlinear dynamics of small-scale Alfvén waves

Mallet¹,

Dorfman²,

Abler³

et al. 2023

Preprint

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“…Extensive prior work has focused on the properties of linear Alfvén waves [5,[28][29][30]. Studies of the nonlinear properties of Alfvén waves have also been performed on the LAPD; in these experiments, two launched Alfvén waves nonlinearly interact to drive a nonresonant mode [31], a drift wave [32], an acoustic mode [33,34], or an Alfvén wave [35].…”

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confidence: 99%

Observation of an Alfvén Wave Parametric Instability in a Laboratory Plasma

Dorfman

Carter

2016

Phys. Rev. Lett.

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A shear Alfvén wave parametric instability is observed for the first time in the laboratory. When a single finite ω/Ωi kinetic Alfvén wave (KAW) is launched in the Large Plasma Device above a threshold amplitude, three daughter modes are produced. These daughter modes have frequencies and parallel wave numbers that are consistent with copropagating KAW sidebands and a low frequency nonresonant mode. The observed process is parametric in nature, with the frequency of the daughter modes varying as a function of pump wave amplitude. The daughter modes are spatially localized on a gradient of the pump wave magnetic field amplitude in the plane perpendicular to the background field, suggesting that perpendicular nonlinear forces (and therefore k ⊥ of the pump wave) play an important role in the instability process. Despite this, modulational instability theory with k ⊥ = 0 has several features in common with the observed nonresonant mode and Alfvén wave sidebands.PACS numbers: 52.35. Mw, 52.35.Bj Alfvén waves, a fundamental mode of magnetized plasmas, are ubiquitous in space, astrophysical, and laboratory plasmas. While the linear behavior of these waves has been extensively studied [1][2][3][4][5], nonlinear effects are important in many real systems, including the solar wind and solar corona. Theoretical predictions show that these Alfvén waves may be unstable to various parametric instabilities (e.g., Refs. [6-8]) even at very low amplitudes (δB/B < 10 −3 ). Parametric instabilities could contribute to coronal heating [9], the observed spectrum and cross-helicity of solar wind turbulence [10][11][12], and damping of fast magnetosonic waves in fusion plasmas [13,14].An abundance of theoretical work [6,7,[15][16][17][18][19] has found three types of parametric instabilities for a k ⊥ = 0 Alfvén wave: decay, modulational, and beat. The decay instability is the most widely known and involves the decay of a forward propagating Alfvén wave into a backward propagating Alfvén wave and a forward propagating sound wave. By contrast, the modulational instability results in forward propagating upper and lower Alfvénic sidebands as well as well as a nonresonant acoustic mode at the sideband separation frequency. To allow the forward propagating waves to interact, the pump wave must be dispersive-therefore the modulational instability at k ⊥ = 0 requires finite ω/Ω i through inclusion of Hall effects [7]. Ponderomotive coupling between the pump and sideband Alfvén modes self-consistently drives the nonresonant density perturbation parallel to the background magnetic field. In this context, "nonresonant" means that the mode does not satisfy a dispersion relation in the absence of the instability drive; this is also called a quasimode in the fusion community [20,21].Both shear Alfvén wave decay and modulational instabilities have been produced in numerical simulations [11,[22][23][24][25], but observational evidence is limited. Observations in the ion foreshock region upstream of the bow shock in the Earth's magnetosphere have...

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“…302,303 Recent experimental work in the Large Plasma Device at UCLA has focused on exploring the physics of parametric instabilities. Initial experiments demonstrated the resonant excitation of acoustic modes by large-amplitude Alfvén waves, 304,305 followed by the successful measurement of an Alfvén wave parametric instability in the laboratory. 306 Finally, a number of other important instabilities in space and astrophysical plasmas are susceptible to investigation in the laboratory, including the magnetic buoyancy instabilities 307 that play a key role in the solar dynamo and drive space weather eruptions, the gradient drift coupling (GDC) instability that can potentially enhance magnetic reconnection in astrophysical plasmas, 308,309 and current-driven instabilities of coronal arches.…”

Section: E Kinetic and Fluid Instabilitiesmentioning

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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Non-linear Alfvén wave interaction leading to resonant excitation of an acoustic mode in the laboratorya)

Cited by 7 publications

References 32 publications

Nonlinear dynamics of small-scale Alfvén waves

Nonlinear dynamics of small-scale Alfvén waves

Observation of an Alfvén Wave Parametric Instability in a Laboratory Plasma

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

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