Laboratory Observations of Electron Heating and Non-Maxwellian Distributions at the Kinetic Scale during Electron-Only Magnetic Reconnection

Direct observations of pure electron outflow in magnetic reconnection

“…These processes include the formation of electron current sheets and outflows within an electron dissipation region [12][13][14] , and electron temperature anisotropy excitation of whistler waves 15,16,18 . The magnetic reconnection without coupling to ions is observed in the magnetosheath because of tiny spatial and temporal scales of turbulent plasmas 14 .The basic properties of "electron-only reconnection", which can lead to Sweet-Parker reconnection in magnetohydrodynamics (MHD) limit, have been investigated 7,[19][20][21] ; numerical simulations show that the electron-only reconnection starts to transit to ion-coupled (MHD) reconnection at the spatial scale of 10d i , where d i is the ion skin depth 19 . The electron outflows close to the electron Alfvén velocity are observed 7,14,20,21 .…”

“…The magnetic reconnection without coupling to ions is observed in the magnetosheath because of tiny spatial and temporal scales of turbulent plasmas 14 .The basic properties of "electron-only reconnection", which can lead to Sweet-Parker reconnection in magnetohydrodynamics (MHD) limit, have been investigated 7,[19][20][21] ; numerical simulations show that the electron-only reconnection starts to transit to ion-coupled (MHD) reconnection at the spatial scale of 10d i , where d i is the ion skin depth 19 . The electron outflows close to the electron Alfvén velocity are observed 7,14,20,21 . These fast magnetic reconnection processes can be expressed as standing whistler waves (or standing kinetic Alfvén waves in the presence of a guide field), as MHD phenomena can be treated as a superposition of Alfvén waves [22][23][24][25] .…”

Electron-scale reconnection in three-dimensional shock turbulence

“…This differs from the standard picture of collisionless reconnection (Ishizawa et al, 2004;Malyshkin, 2008;Yamada, 2011), where the reconnection region consists of an electron-scale layer within a wider ion-scale diffusion region. These electron-only reconnection regions have been observed in the Earth's magnetosheath and shock transition region (Phan et al, 2018;Gingell et al, 2020), foreshock (Wang et al, 2020;Liu et al, 2020), magnetotail (S. Lu et al, 2020) and laboratory experiments (Shi et al, 2022).…”

Electron‐Scale Reconnection in Three‐Dimensional Shock Turbulence

“…This differs from the standard picture of collisionless reconnection (Ishizawa et al., 2004; Malyshkin, 2008; Yamada, 2011), where the reconnection region consists of an electron‐scale layer within a wider ion‐scale diffusion region. These electron‐only reconnection regions have been observed in the Earth's magnetosheath and shock transition region (Gingell et al., 2019, 2020, 2021; Phan et al., 2018; Stawarz et al., 2022; Wang et al., 2019), foreshock (Liu et al., 2020; Wang et al., 2020), magnetotail (S. Lu et al., 2020) and laboratory experiments (Shi et al., 2022).…”