Diffusive scattering of electrons by electron holes around injection fronts

Abstract

Van Allen Probes have detected nonlinear electrostatic spikes around injection fronts in the outer radiation belt. These spikes include electron holes (EH), double layers, and more complicated solitary waves. We show that EHs can efficiently scatter electrons due to their substantial transverse electric fields. Although the electron scattering driven by EHs is diffusive, it cannot be evaluated via the standard quasi‐linear theory. We derive analytical formulas describing local electron scattering by a single EH and verify them via test particle simulations. We show that the most efficiently scattered are gyroresonant electrons (crossing EH on a time scale comparable to the local electron gyroperiod). We compute bounce‐averaged diffusion coefficients and demonstrate their dependence on the EH spatial distribution (latitudinal extent and spatial filling factor) and individual EH parameters (amplitude of electrostatic potential, velocity, and spatial scales). We show that EHs can drive pitch angle scattering of ≲5 keV electrons at rates 10−2−10−4 s−1 and, hence, can contribute to electron losses and conjugated diffuse aurora brightenings. The momentum and pitch angle scattering rates can be comparable, so that EHs can also provide efficient electron heating. The scattering rates driven by EHs at L shells L ∼ 5–8 are comparable to those due to chorus waves and may exceed those due to electron cyclotron harmonics.

A Census of Plasma Waves and Structures Associated With an Injection Front in the Inner Magnetosphere

“…The properties of phase space holes observed by the Burst 1 data are now compared with phase space hole properties derived from Burst 2 observations, specifically with Vasko, Agapitov, Mozer, Artemyev, Drake, and Kuzichev (), where the amplitude, phase velocity, magnetic spike signature, parallel width, and potential depth of 100 electron phase space holes were examined using Burst 2 data. Vasko, Agapitov, Mozer, Artemyev, Krasnoselskikh, and Bonnell () used the Vasko, Agapitov, Mozer, Artemyev, Drake, and Kuzichev () results to define typical electron hole properties from which they derived diffusion coefficients describing the diffusive scattering of electrons by electron phase space holes. The diffusion coefficients computed by Vasko, Agapitov, Mozer, Artemyev, Krasnoselskikh, and Bonnell () were based on electron hole parameters as determined using amplitude‐biased Burst 2 data.…”

“…Using the Van Allen Probes high‐resolution electric and magnetic field time series data (burst data), researchers have demonstrated that this broadband power is due to waves and structures such as electron‐acoustic solitons (Agapitov et al, ; Mozer et al, ; Vasko, Agapitov, Mozer, Bonnell, et al, ), ion‐acoustic double layers (Malaspina et al, ), electron phase space holes (Malaspina et al, ; Vasko, Agapitov, Mozer, Artemyev et al, ; Vasko, Agapitov, Mozer, Artemyev, Krasnoselskikh, & Bonnell, ), nonlinear whistler mode waves (Gao et al, ; Mozer et al, ), and kinetic Alfvén waves (Chaston et al, , ; Malaspina, Claudepierre, et al, ).…”

“…Each kinetic structure type supports a unique set of wave‐particle interactions with the potential to cause significant particle acceleration and scattering (Artemyev et al, , ; Chaston et al, , ; Mozer et al, ; Osmane & Pulkkinen, ; Osmane et al, ; Vasko, Agapitov, Mozer, & Artemyev, ; Vasko, Agapitov, Mozer, Artemyev, Krasnoselskikh, & Bonnell, ). It was also shown that the occurrence of these kinetic structures in the inner magnetosphere is highly correlated with plasma boundaries such as injection fronts, the plasmapause, and the earthward edge of the plasma sheet (Malaspina, Wygant, et al, ).…”

Multispacecraft Analysis of Electron Holes

“…They play an important role in plasma dynamics (e.g., Hutchinson, 2017, and references therein); in particular, they provide a mechanism for scattering and heating of electrons (Vasko et al, 2017) and can increase the rate of magnetic reconnection (Drake et al, 2003). They play an important role in plasma dynamics (e.g., Hutchinson, 2017, and references therein); in particular, they provide a mechanism for scattering and heating of electrons (Vasko et al, 2017) and can increase the rate of magnetic reconnection (Drake et al, 2003).…”

Pulsating auroras produced by interactions of electrons and time domain structures

“…Theory [ Artemyev et al ., ; Vasko et al ., ; Vasko et al ., , ], earlier observations [ Mozer et al ., , , ], and the observations in this paper all show that TDSs accelerate and pitch angles scatter keV equatorial electrons to lower altitude mirror points where they either produce auroras or are further processed by lower altitude TDS to create auroras on field lines having the TDS. The typical speed of a TDS is ~5000 km/s, which is the speed of a 70 eV electron.…”