Dr Louis Richard: Publications

Statistical Study of Betatron and Fermi Electron Acceleration at Dipolarization Fronts

Geophysical Research Letters American Geophysical Union (AGU) 53:15 (2026) e2026GL122885

Authors:

A Kolokotronis, DB Graham, Yu V Khotyaintsev, C Norgren, K Steinvall, L Richard

Abstract:

Abstract Magnetic reconnection jets in Earth's magnetotail are regions of electron heating and acceleration. They are often associated with dipolarization fronts (DFs), which are characterized by sharp increases in the northward magnetic field component . Electrons can be accelerated at DFs mainly through the betatron and Fermi mechanisms. We perform a statistical study of betatron and Fermi electron rate of energy change at Earthward‐propagating DFs observed by the Magnetospheric Multiscale (MMS) spacecraft. Our results show that betatron acceleration is dominant ahead of DFs, where suprathermal electron fluxes perpendicular to the magnetic field are detected. Up to ion inertial lengths inside the outflow, Fermi acceleration acts on the low‐density electron population, potentially driving them to high energies (∼100 ). Spatially in the magnetotail, betatron acceleration is statistically larger near the most probable X‐line location, while Fermi‐dominated events are observed closer to the Earth.

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Occurrence of Flat‐Top Electron Velocity Distributions in Magnetotail Plasma Jets

Geophysical Research Letters American Geophysical Union (AGU) 53:12 (2026) e2026GL123161

Authors:

L Richard, Yu V Khotyaintsev, C Norgren

Abstract:

Abstract Non‐Maxwellian electron velocity distributions (eVDFs) are ubiquitous in collisionless plasmas. For example, various types of non‐Maxwellian eVDFs exist in magnetic reconnection jets in the Earth's magnetotail. At thermal energies, eVDF can be flat‐topped due to electron trapping associated with magnetic reconnection. However, the occurrence of such eVDFs in magnetotail reconnection remains largely unconstrained. Here, we statistically investigate flat‐top eVDFs in fast plasma jets in the magnetotail using a new method for classifying eVDFs. We show that at least of the eVDFs in the jets are flat‐tops. In addition, we find that most jets exhibit flat‐top eVDFs, indicating that this signature of parallel acceleration and electron streaming is characteristic of the jets. We find that these flat‐top eVDFs are localized within an ion‐inertial‐length‐scale region near the edges of the current sheet and the ion diffusion region. Our results highlight the importance of flat‐top eVDFs in non‐local thermodynamic equilibrium collisionless plasmas.

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Ion Anisotropy in Earth's Magnetotail: Importance of High‐Energy Ions

Journal of Geophysical Research: Space Physics American Geophysical Union (AGU) 131:6 (2026) e2026JA035223

Authors:

Xiaofei Shi, Vassilis Angelopoulos, Louis Richard, Anton Artemyev

Abstract:

Abstract The reconfiguration of the magnetotail current sheet during substorms often includes the formation of a thin current sheet (TCS) with a strong magnetic field line tension force. This force cannot be balanced by isotropic plasma pressure gradients, and force balance in such a TCS requires ion anisotropy and/or agyrotropy of plasma pressure. A statistical investigation of these plasma properties in the magnetotail is challenging because a significant contribution to ion anisotropy or agyrotropy stems from the suprathermal ion population, which often has energies beyond the upper limit of electrostatic analyzer measurements. In this study, we compare ion measurements from Cluster, MMS, and THEMIS to investigate the ion anisotropy in the magnetotail current sheet. We show that the central region of the magnetotail is characterized by transverse anisotropy of suprathermal ions, whereas subthermal field‐aligned anisotropic ions populate the magnetotail current sheet boundaries. Our results indicate that different ion populations (subthermal, thermal, and suprathermal ions) exhibit distinct behaviors within the current sheet, showing that different combinations of these populations contribute differently to the stability of current sheets.

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Finding Local Parallel Electric Fields in Magnetotail Reconnection Using a Two‐Spacecraft Method

Geophysical Research Letters American Geophysical Union (AGU) 53:6 (2026) e2025GL119588

Authors:

JD White, Yu V Khotyaintsev, C Norgren, DB Graham, L Richard

Abstract:

Abstract We investigate the use of a novel two‐spacecraft Liouville‐mapping method using data from the Magnetospheric Multiscale mission to determine local magnetic‐field‐aligned (parallel) electric fields in the Earth's magnetotail. The method detects the presence of local acceleration potentials by mapping phase‐space density between electron velocity distribution functions from two field‐aligned spacecraft upstream and downstream of acceleration regions. Applying the method to a magnetic reconnection event, we find that local parallel electric fields near the current sheet (CS) center are, on average, directed away from the center, resulting from the need to maintain quasi‐neutrality across the CS. Despite significant measurement uncertainties, we find that the local acceleration potentials are smaller than the total acceleration potential, typically 1%–2% on average and up to 9% for individual measurements. This indicates that many potential drops, over distances much larger than the spacecraft separations, contribute to the net work done on electrons by parallel electric fields.

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Statistical study of Field-Aligned Currents in the Ionosphere associated with Bursty Bulk Flows Events

(2026)

Authors:

Vanina Lanabere, Andrew P Dimmock, Adrian Blagau, Stephan Christoph Buchert, Octav Marghitu, Louis Richard

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Dr Louis Richard

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Statistical Study of Betatron and Fermi Electron Acceleration at Dipolarization Fronts

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Abstract:

Occurrence of Flat‐Top Electron Velocity Distributions in Magnetotail Plasma Jets

Authors:

Abstract:

Ion Anisotropy in Earth's Magnetotail: Importance of High‐Energy Ions

Authors:

Abstract:

Finding Local Parallel Electric Fields in Magnetotail Reconnection Using a Two‐Spacecraft Method

Authors:

Abstract:

Statistical study of Field-Aligned Currents in the Ionosphere associated with Bursty Bulk Flows Events

Authors:

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Dr Louis Richard

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Statistical Study of Betatron and Fermi Electron Acceleration at Dipolarization Fronts

Authors:

Abstract:

Occurrence of Flat‐Top Electron Velocity Distributions in Magnetotail Plasma Jets

Authors:

Abstract:

Ion Anisotropy in Earth's Magnetotail: Importance of High‐Energy Ions

Authors:

Abstract:

Finding Local Parallel Electric Fields in Magnetotail Reconnection Using a Two‐Spacecraft Method

Authors:

Abstract:

Statistical study of Field-Aligned Currents in the Ionosphere associated with Bursty Bulk Flows Events

Authors: