Subcritical Growth of Electron Phase-space Holes in Planetary Radiation Belts

Osmane, Adnane; Turner, D. L.; Wilson, L. B.; Dimmock, A. P.; Pulkkinen, Tuija

doi:10.3847/1538-4357/aa8367

Cited by 7 publications

(4 citation statements)

References 54 publications

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“…This property of nonlinear systems is well known among astrophysical and fluid turbulence research and underlies the assumption of critical balance, in which the transit time becomes comparable to the nonlinear interaction time (Goldreich & Sridhar 1995). 11 Observational evidence and theoretical studies of fast and nonlinear processes at the heart of the Earth's radiation belts have become substantial in the last 15 yr but are typically associated with electron-scale whistlers and chorus (Bortnik et al 2008;Cattell et al 2008;Cully et al 2008;Albert et al 2012;Artemyev et al 2012Artemyev et al , 2015Mozer et al 2013;Malaspina et al 2014;Santolík et al 2014;Agapitov et al 2015;Osmane et al 2016Osmane et al , 2017Tao et al 2020;Omura 2021) and ion-scale EMIC waves (Hendry et al 2019;Bortnik et al 2022;Grach et al 2022). With the exceptions of the numerical studies of Li et al ( , 2018, Degeling et al (2008), Hudson et al (2017), and extreme driving events such as the one reported by Kanekal et al (2016), fast and higher-order radial transport are rarely considered and have yet to be accounted for in global models.…”

Section: On the Need For A New Theoretical Framework Of Radial Transportmentioning

confidence: 99%

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Osmane,

Kilpua,

George

et al. 2023

ApJS

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Observational studies of the Earth’s radiation belts indicate that Alfvénic fluctuations in the frequency range of 2–25 mHz accelerate electrons to relativistic energies. For decades, statistical models of radiation belts have quantified the impact of Alfvénic waves in terms of quasi-linear diffusion. However, quasi-linear models are inadequate to quantify Alfvénic radial transport occurring on timescales comparable to the azimuthal drift period of 0.1–10 MeV electrons. With recent advances in observational methodologies offering coverage of the Earth’s radiation belts on fast timescales, a theoretical framework that distinguishes between fast and diffusive radial transport can be tested for the first time in situ. In this report, we present a drift-kinetic description of radial transport for planetary radiation belts. We characterize fast linear processes and determine the conditions under which higher-order effects become dynamically significant. In the linear regime, wave–particle interactions are categorized in terms of resonant and nonresonant responses. We demonstrate that the phenomenon of zebra stripes is nonresonant and can originate from injection events in the inner radiation belts. We derive a radial diffusion coefficient for a field model that satisfies Faraday’s law and that contains two terms: one scaling as L 10 independent of the azimuthal number m, and a second scaling as m 2 L 6. In the higher-order regime, azimuthally symmetric waves with properties consistent with in situ measurements can energize 10–100 keV electrons in less than a drift period. This process provides new evidence that acceleration by Alfvénic waves in radiation belts cannot be fully contained within diffusive models.

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Section: On the Need For A New Theoretical Framework Of Radial Transportmentioning

confidence: 99%

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Osmane,

Kilpua,

George

et al. 2023

ApJS

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“…The simplest nonlinear analytic approach to the experimentally and numerically observable class of excitations [15][16][17][18][19][20][21][22] works by invoking a fixed ionic background and a thermal Maxwellian approximation for equilibrium electron distribution in the Vlasov analysis, for example in all well known linear [? ? ]…”

Section: Introductionmentioning

confidence: 99%

Ultra slow electron holes in collisionless plasmas: Stability at high ion temperature

2020

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Numerical simulations recover ultra slow electron holes (EH) of electron-acoustic genre propagating stably well below the ion acoustic speed where the ion response disallows any known pure electron perturbation. The reason of stability of EH at high ion temperature (Ti > Te) is traced to the loss of neutralizing cold ion response. In a background of cold ions, θ = Te/Ti ≫ 1, they have an ion compression that accelerates to jump over a forbidden velocity gap and settle on the high velocity tail of the electron distribution fe, confirming to a recently identified limit of the nonlinear dispersion relation. For θ = Te/Ti ≤ 1, however, the warm ions begin to supplement the electron response transforming the ion compression to decompression at the hole location and triggering multiplicity of the scales in trapped electron population which prompts an immediate generalization of the basic EH theory.

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“…Subcritically driven turbulence of plasma state remains a less understood process, often presenting its strong signatures in nature [1,2], experiments [3][4][5] and in simulations [6][7][8][9][10][11] of collisionless hot plasmas. Underlying this are instabilities of nonlinear collective eigenmodes of nonthermal distributions rather than those of the normal linear eigenmodes of a thermalized distribution f 0 , recoverable by selecting the corresponding poles of dispersion function to perform the Landau integral, yielding f f v 0 0 ¢ º ¶ ¶ as a unique driver for the microinstabilites.…”

Section: Introductionmentioning

confidence: 99%

Electron hole instability as a primordial step towards sustained intermittent turbulence in linearly subcritical plasmas

2018

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Electron and ion holes are highly stable nonlinear structures met omnipresently in driven collisionless hot plasmas. A mechanism destabilizing small perturbations into holes is essential for an often witnessed but less understood subcritically driven intermittent plasma turbulence. In this paper we show how a tiny, eddy-like, non-topological electron seed fluctuation can trigger an unstable evolution deep in the linearly damped region, a process being controlled by the trapping nonlinearity and hence being beyond the realm of the Landau scenario. After a (transient) transition phase modes of the privileged spectrum of cnoidal electron and ion holes are excited which in the present case consist of a solitary electron hole (SEH), two counter-propagating 'Langmuir' modes (plasma oscillation), and an ion acoustic mode. A quantitative explanation involves a nonlinear dispersion relation with a forbidden regime and the negative energy character of the SEH, properties being inherent in Schamel's model of undamped Vlasov-Poisson structures identified here as lowest order trapped particle equilibria. An important role in the final adaption of nonlinear plasma eigenmodes is played by a deterministic response of trapped electrons which facilitates transfer of energy from electron thermal energy to an ion acoustic nonuniformity, accelerating the SEH and positioning it into the right place assigned by the theory.

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Subcritical Growth of Electron Phase-space Holes in Planetary Radiation Belts

Cited by 7 publications

References 54 publications

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Radial Transport in the Earth’s Radiation Belts: Linear, Quasi-linear, and Higher-order Processes

Ultra slow electron holes in collisionless plasmas: Stability at high ion temperature

Electron hole instability as a primordial step towards sustained intermittent turbulence in linearly subcritical plasmas

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