Particle pitch angle diffusion due to nonadiabatic effects in the plasma sheet

Gray, P. C.; Lee, L. C.

doi:10.1029/ja087ia09p07445

Cited by 69 publications

(39 citation statements)

References 22 publications

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“…On the contrary, ions in the supra-thermal energy regime are expected to behave in a non-adiabatic manner and hence their pitch angle distribution looses its anisotropic features. This follows from the fact that ions are subjected to a continuous isotropization because of random changes in the magnetic moment each time they cross the middle of the plasma sheet, experiencing a spatial variation of the magnetic field on the order of their gyroradius (collisionless pitch angle scattering) (Gray and Lee, 1982). The above mechanism further forces energetic ions to execute Speiser orbits and as a result, the ions return to the current sheet in a location much closer to the Earth than the one from which they were ejected.…”

Section: Particle Energization and Non-adiabaticitymentioning

confidence: 99%

Two distinct energetic electron populations of different origin in the Earth's magnetotail: a Cluster case study

et al. 2006

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Abstract. Energetic electrons (E≥30 keV) travelling along and perpendicular to the magnetic field lines have been observed in the magnetotail at L∼17:00 and 22:00 MLT during the recovery phase of a storm-time substorm on 7 October 2002. Three-dimensional electron distributions of the full unit sphere obtained from the IES/RAPID sensor system demonstrated a rather complicated and random behavior of the energetic electrons. Occasionally these electrons were appearing to travel parallel, perpendicular, or in both directions, relative to the magnetic field direction, forming in this way bi-directional, perpendicular-peaked, and mixed distributions. The electron enhancements occurred while the Cluster spacecraft were on closed field lines in the central plasma sheet approaching the neutral sheet from the northern tail lobe. Magnetic field and energetic particle measurements have been used from geosynchronous and Cluster satellites, in order to describe the general context of the event and then give a possible interpretation regarding the occurrence of the electron anisotropies observed by the IES/RAPID spectrometer on board Cluster. According to geosynchronous measurements an electron dispersionless ejection is very well correlated with a dipolar re-configuration of the magnetic field. The latter fact supports the idea that electrons and, in general, particle ejections at geosynchronous altitude are directly related to electric fields arising from field dipolarization caused by current disruption. Also, having as a main objective the understanding of the way 3-D electron distributions are formed, we have analyzed electron energy spectra along and perpendicular to the magnetic field direction, demonstrating the fact that the electron population consists of two distinct components acting independently and in a random manner relative to each other. This leads to the conclusion that these two electron populations along and perpendicular to the field are generated at different remote locations at Correspondence to: I. I. Vogiatzis (ivogiatz@ee.duth.gr) different rates. The main conclusion of the present paper is that the perpendicular-peaked electron enhancements (electrons with pitch angle around 90 degrees, subjected mainly to curvature drift) observed by Cluster are produced in a remote location duskward of the satellite location, due to the longitudinal and tailward expansion of a current disruption region, and subsequently transported to the Cluster location by means of curvature drift. On the other hand, bi-directional electrons (electrons with pitch angle around 0 and 180 degrees, bouncing mainly along the field lines) are believed to be generated in the vicinity of the neutral sheet or around an X-type region, as suggested by a plethora of previous studies. Finally, in the Discussion section, we make an attempt to present in a more thorough way the substorm model developed by Vogiatzis et al. (2005), which is intimately related to the importance of X-line formation for the initiation of a substorm.

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Section: Particle Energization and Non-adiabaticitymentioning

confidence: 99%

Two distinct energetic electron populations of different origin in the Earth's magnetotail: a Cluster case study

et al. 2006

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“…7(a) and 7(b)). This irreversibility is due to the non-adiabaticity in the particle behavior: At the bottom panels of Figs the ratio, (particle gyroradius p)/(field curvature radius Rc) as a measure of non-adiabaticity (Gray and Lee, 1982). Since these ratios become of -1 after the type-I energization, the particle magnetic moments are not conserved.…”

Section: Traveling Of the Energized Particles Around A Plasmoidmentioning

confidence: 99%

“…These studies show the complexity and importance of the particle motion near the neutral sheet, where the adiabaticity of the particle motion is easily violated. Calculations of test particle trajectories in stationary neutral sheet were also studied by several authors (Speiser, 1965;Sonnerup, 1971;Wagner et al, 1979;Gray and Lee, 1982). Wagner et al have classified the particle orbits into adiabatic, transitional, and non-adiabatic case, according to the field geometry.…”

Section: Introductionmentioning

confidence: 99%

“…no net energization) and the final pitch angle is close to the K. TSEH000HI and T. TERASAWA initial value, while non-adiabatic orbits undergo a net cross-tail displacement as they pass through the plasma sheet (gain energy), and initial and final pitch angles lose their relationship. Gray and Lee (1982) have shown that for a large value of p/Re the random change in the magnetic moment takes place as a particle passes the midplane of the plasma sheet. (R, is the characteristic length over which the field varies, here the radius of the curvature, and p the gyroradius of the particle.)…”

Section: Introductionmentioning

confidence: 99%

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The Energization of Cold Ions around a Plasmoid in the Magnetotail.

Tsubouchi

Terasawa

1995

J. geomagn. geoelec

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We study numerically the interaction of cold ionospheric ions in the tail lobe with a plasmoid propagating steadily in the tailward direction. We have found that significant energization of cold ions occurs at the encounter with a plasmoid, where three types of the interaction processes are taking place: First, ions show gradient and curvature drift motions as the plasmoid approaches. These ions are accelerated up to -1 keV by the cross-tail electric field accompanying with the plasmoid motion (type-I energization). Second, some of the ions get large pitch angles after the type-I acceleration, and then mirror reflected by the plasmoid. These ions are accelerated up to 10 keV after the reflection (type-II energization). Third, the motions of the ions near the plasmoid become highly non-adiabatic, because their gyroradii become comparable to the field-line curvature radius after the type-I energization. Consequently the energy distribution of these ions is broadened in the trailing side of the plasmoid (type-III energization). These theoretical results are successfully compared with the recent GEOTAIL observation showing the dynamic interaction of cold ions with a plasmoid and their subsequent energization.

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“…This simplification comes directly from our assumption about strong localization of a magnetic field perturbation, i.e., the scale is substantially smaller than the scale of dipole field inhomogeneity ∼ LR E . This model is widely used for investigations of charged particle scattering due to nonadiabatic motion [e.g., Gray and Lee, 1982;Birmingham, 1984;Delcourt et al, 1995]. The Hamiltonian of relativistic electrons with the rest mass m and the charge −e in this magnetic field has the following form:…”

Section: Model Of the Electron Scatteringmentioning

confidence: 99%

Butterfly pitch angle distribution of relativistic electrons in the outer radiation belt: Evidence of nonadiabatic scattering

et al. 2015

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In this paper we investigate the scattering of relativistic electrons in the nightside outer radiation belt (around the geostationary orbit). We consider the particular case of low geomagnetic activity (|D st | < 20 nT), quiet conditions in the solar wind, and absence of whistler wave emissions. For such conditions we find several events of Van Allen probe observations of butterfly pitch angle distributions of relativistic electrons (energies about 1-3 MeV). Many previous publications have described such pitch angle distributions over a wide energy range as due to the combined effect of outward radial diffusion and magnetopause shadowing. In this paper we discuss another mechanism that produces butterfly distributions over a limited range of electron energies. We suggest that such distributions can be shaped due to relativistic electron scattering in the equatorial plane of magnetic field lines that are locally deformed by currents of hot ions injected into the inner magnetosphere. Analytical estimates, test particle simulations, and observations of the AE index support this scenario. We conclude that even in the rather quiet magnetosphere, small scale (magnetic local time (MLT)-localized) injection of hot ions from the magnetotail can likely influence the relativistic electron scattering. Thus, observations of butterfly pitch angle distributions can serve as an indicator of magnetic field deformations in the nightside inner magnetosphere. We briefly discuss possible theoretical approaches and problems for modeling such nonadiabatic electron scattering.

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Particle pitch angle diffusion due to nonadiabatic effects in the plasma sheet

Cited by 69 publications

References 22 publications

Two distinct energetic electron populations of different origin in the Earth's magnetotail: a Cluster case study

Two distinct energetic electron populations of different origin in the Earth's magnetotail: a Cluster case study

The Energization of Cold Ions around a Plasmoid in the Magnetotail.

Butterfly pitch angle distribution of relativistic electrons in the outer radiation belt: Evidence of nonadiabatic scattering

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