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R B Torbert - One of the best experts on this subject based on the ideXlab platform.
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Electron crescent distributions as a manifestation of diamagnetic drift in an Electron scale current sheet magnetospheric multiscale observations using new 7 5 ms fast plasma investigation moments
Geophysical Research Letters, 2018Co-Authors: R B Torbert, J Dorelli, A C Rager, Daniel J Gershman, Vadim M Uritsky, L A AvanovAbstract:Author(s): Rager, AC; Dorelli, JC; Gershman, DJ; Uritsky, V; Avanov, LA; Torbert, RB; Burch, JL; Ergun, RE; Egedal, J; Schiff, C; Shuster, JR; Giles, BL; Paterson, WR; Pollock, CJ; Strangeway, RJ; Russell, CT; Lavraud, B; Coffey, VN; Saito, Y | Abstract: We report Magnetospheric Multiscale observations of Electron Pressure gradient electric fields near a magnetic reconnection diffusion region using a new technique for extracting 7.5 ms Electron moments from the Fast Plasma Investigation. We find that the deviation of the perpendicular Electron bulk velocity from E × B drift in the interval where the out-of-plane current density is increasing can be explained by the diamagnetic drift. In the interval where the out-of-plane current is transitioning to in-plane current, the Electron momentum equation is not satisfied at 7.5 ms resolution.
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Electron crescent distributions as a manifestation of diamagnetic drift in an Electron scale current sheet magnetospheric multiscale observations using new 7 5 ms fast plasma investigation moments
Geophysical Research Letters, 2018Co-Authors: R B Torbert, J Dorelli, A C Rager, Daniel J Gershman, Vadim M Uritsky, L A AvanovAbstract:We report Magnetospheric Multiscale observations of Electron Pressure gradient electric fields near a magnetic reconnection diffusion region using a new technique for extracting 7.5 ms Electron moments from the Fast Plasma Investigation. We find that the deviation of the perpendicular Electron bulk velocity from E × B drift in the interval where the out-of-plane current density is increasing can be explained by the diamagnetic drift. In the interval where the out-of-plane current is transitioning to in-plane current, the Electron momentum equation is not satisfied at 7.5 ms resolution.
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magnetospheric multiscale observations of the Electron diffusion region of large guide field magnetic reconnection
Physical Review Letters, 2016Co-Authors: S Eriksson, F D Wilder, S J Schwartz, P A Cassak, R B Torbert, T D Phan, R. E. Ergun, J. L. Burch, Lijen Chen, Benoit LavraudAbstract:We report observations from the Magnetospheric Multiscale (MMS) satellites of a large guide field magnetic reconnection event. The observations suggest that two of the four MMS spacecraft sampled the Electron diffusion region, whereas the other two spacecraft detected the exhaust jet from the event. The guide magnetic field amplitude is approximately 4 times that of the reconnecting field. The event is accompanied by a significant parallel electric field (E(sub parallel lines) that is larger than predicted by simulations. The high-speed (approximately 300 km/s) crossing of the Electron diffusion region limited the data set to one complete Electron distribution inside of the Electron diffusion region, which shows significant parallel heating. The data suggest that E(sub parallel lines) is balanced by a combination of Electron inertia and a parallel gradient of the gyrotropic Electron Pressure.
A C Rager - One of the best experts on this subject based on the ideXlab platform.
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Pressure tensor elements breaking the frozen in law during reconnection in earth s magnetotail
Physical Review Letters, 2019Co-Authors: J Egedal, William Daughton, Blake A Wetherton, J Dorelli, D J Gershman, A C RagerAbstract:Aided by fully kinetic simulations, spacecraft observations of magnetic reconnection in Earth's magnetotail are analyzed. The structure of the Electron diffusion region is in quantitative agreement with the numerical model. Of special interest, the spacecraft data reveal how reconnection is mediated by off-diagonal stress in the Electron Pressure tensor breaking the frozen-in law of the Electron fluid.
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Electron crescent distributions as a manifestation of diamagnetic drift in an Electron scale current sheet magnetospheric multiscale observations using new 7 5 ms fast plasma investigation moments
Geophysical Research Letters, 2018Co-Authors: R B Torbert, J Dorelli, A C Rager, Daniel J Gershman, Vadim M Uritsky, L A AvanovAbstract:We report Magnetospheric Multiscale observations of Electron Pressure gradient electric fields near a magnetic reconnection diffusion region using a new technique for extracting 7.5 ms Electron moments from the Fast Plasma Investigation. We find that the deviation of the perpendicular Electron bulk velocity from E × B drift in the interval where the out-of-plane current density is increasing can be explained by the diamagnetic drift. In the interval where the out-of-plane current is transitioning to in-plane current, the Electron momentum equation is not satisfied at 7.5 ms resolution.
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Electron crescent distributions as a manifestation of diamagnetic drift in an Electron scale current sheet magnetospheric multiscale observations using new 7 5 ms fast plasma investigation moments
Geophysical Research Letters, 2018Co-Authors: R B Torbert, J Dorelli, A C Rager, Daniel J Gershman, Vadim M Uritsky, L A AvanovAbstract:Author(s): Rager, AC; Dorelli, JC; Gershman, DJ; Uritsky, V; Avanov, LA; Torbert, RB; Burch, JL; Ergun, RE; Egedal, J; Schiff, C; Shuster, JR; Giles, BL; Paterson, WR; Pollock, CJ; Strangeway, RJ; Russell, CT; Lavraud, B; Coffey, VN; Saito, Y | Abstract: We report Magnetospheric Multiscale observations of Electron Pressure gradient electric fields near a magnetic reconnection diffusion region using a new technique for extracting 7.5 ms Electron moments from the Fast Plasma Investigation. We find that the deviation of the perpendicular Electron bulk velocity from E × B drift in the interval where the out-of-plane current density is increasing can be explained by the diamagnetic drift. In the interval where the out-of-plane current is transitioning to in-plane current, the Electron momentum equation is not satisfied at 7.5 ms resolution.
William Daughton - One of the best experts on this subject based on the ideXlab platform.
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Pressure tensor elements breaking the frozen in law during reconnection in earth s magnetotail
Physical Review Letters, 2019Co-Authors: J Egedal, William Daughton, Blake A Wetherton, J Dorelli, D J Gershman, A C RagerAbstract:Aided by fully kinetic simulations, spacecraft observations of magnetic reconnection in Earth's magnetotail are analyzed. The structure of the Electron diffusion region is in quantitative agreement with the numerical model. Of special interest, the spacecraft data reveal how reconnection is mediated by off-diagonal stress in the Electron Pressure tensor breaking the frozen-in law of the Electron fluid.
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double layer electric fields aiding the production of energetic flat top distributions and superthermal Electrons within magnetic reconnection exhausts
Physics of Plasmas, 2015Co-Authors: J Egedal, William Daughton, A L BorgAbstract:Using a kinetic simulation of magnetic reconnection, it was recently shown that magnetic-field-aligned electric fields (E∥) can be present over large spatial scales in reconnection exhausts. The largest values of E∥ are observed within double layers. The existence of double layers in the Earth's magnetosphere is well documented. In our simulation, their formation is triggered by large parallel streaming of Electrons into the reconnection region. These parallel Electron fluxes are required for maintaining quasi-neutrality of the reconnection region and increase with decreasing values of the normalized Electron Pressure upstream of the reconnection region, βe∞=2μ0ne∞Te∞/B∞2. A threshold (βe∞ < 0.02) is derived for strong double layers to develop. We also document how the Electron confinement, provided in part by the structure in E∥, allows sustained energization by perpendicular electric fields (E⊥). The energization is a consequence of the confined Electrons' chaotic orbital motion that includes drifts ali...
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bifurcated structure of the Electron diffusion region in three dimensional magnetic reconnection
Physical Review Letters, 2013Co-Authors: William Daughton, Homa Karimabadi, Vadim RoytershteynAbstract:Three-dimensional kinetic simulations of magnetic reconnection reveal that the Electron diffusion region is composed of two or more current sheets in regimes with weak magnetic shear angles $\ensuremath{\phi}\ensuremath{\lesssim}80\ifmmode^\circ\else\textdegree\fi{}$. This new morphology is explained by oblique tearing modes which produce flux ropes while simultaneously driving enhanced current at multiple resonance surfaces. This physics persists into the nonlinear regime leading to multiple Electron layers embedded within a larger Alfv\'enic inflow and outflow. Surprisingly, the thickness of these layers and the reconnection rate both remain comparable to two-dimensional models. The parallel electric fields are supported predominantly by the Electron Pressure tensor and Electron inertia, while turbulent dissipation remains small.
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a review of Pressure anisotropy caused by Electron trapping in collisionless plasma and its implications for magnetic reconnection
Physics of Plasmas, 2013Co-Authors: J Egedal, William DaughtonAbstract:From spacecraft data, it is evident that Electron Pressure anisotropy develops in collisionless plasmas. This is in contrast to the results of theoretical investigations, which suggest this anisotropy should be limited. Common for such theoretical studies is that the effects of Electron trapping are not included; simply speaking, Electron trapping is a non-linear effect and is, therefore, eliminated when utilizing the standard methods for linearizing the underlying kinetic equations. Here, we review our recent work on the anisotropy that develops when retaining the effects of Electron trapping. A general analytic model is derived for the Electron guiding center distribution f¯(v∥,v⊥) of an expanding flux tube. The model is consistent with anisotropic distributions observed by spacecraft, and is applied as a fluid closure yielding anisotropic equations of state for the parallel and perpendicular components (relative to the local magnetic field direction) of the Electron Pressure. In the context of reconnection, the new closure accounts for the strong Pressure anisotropy that develops in the reconnection regions. It is shown that for generic reconnection in a collisionless plasma nearly all thermal Electrons are trapped, and dominate the properties of the Electron fluid. A new numerical code is developed implementing the anisotropic closure within the standard two-fluid framework. The code accurately reproduces the detailed structure of the reconnection region observed in fully kinetic simulations. These results emphasize the important role of Pressure anisotropy for the reconnection process. In particular, for reconnection geometries characterized by small values of the normalized upstream Electron Pressure, βe∞, the Pressure anisotropy becomes large with p∥≫p⊥ and strong parallel electric fields develop in conjunction with this anisotropy. The parallel electric fields can be sustained over large spatial scales and, therefore, become important for Electron acceleration.
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regimes of the Electron diffusion region in magnetic reconnection
Physical Review Letters, 2013Co-Authors: A Le, J Egedal, O Ohia, Homa Karimabadi, William Daughton, V S LukinAbstract:: The Electron diffusion region during magnetic reconnection lies in different regimes depending on the Pressure anisotropy, which is regulated by the properties of thermal Electron orbits. In kinetic simulations at the weakest guide fields, pitch angle mixing in velocity space causes the outflow Electron Pressure to become nearly isotropic. Above a threshold guide field that depends on a range of parameters, including the normalized Electron Pressure and the ion-to-Electron mass ratio, Electron Pressure anisotropy develops in the exhaust and supports extended current layers. This new regime with Electron current sheets extending to the system size is also reproduced by fluid simulations with an anisotropic closure for the Electron Pressure. It offers an explanation for recent spacecraft observations.
J Egedal - One of the best experts on this subject based on the ideXlab platform.
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Pressure tensor elements breaking the frozen in law during reconnection in earth s magnetotail
Physical Review Letters, 2019Co-Authors: J Egedal, William Daughton, Blake A Wetherton, J Dorelli, D J Gershman, A C RagerAbstract:Aided by fully kinetic simulations, spacecraft observations of magnetic reconnection in Earth's magnetotail are analyzed. The structure of the Electron diffusion region is in quantitative agreement with the numerical model. Of special interest, the spacecraft data reveal how reconnection is mediated by off-diagonal stress in the Electron Pressure tensor breaking the frozen-in law of the Electron fluid.
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double layer electric fields aiding the production of energetic flat top distributions and superthermal Electrons within magnetic reconnection exhausts
Physics of Plasmas, 2015Co-Authors: J Egedal, William Daughton, A L BorgAbstract:Using a kinetic simulation of magnetic reconnection, it was recently shown that magnetic-field-aligned electric fields (E∥) can be present over large spatial scales in reconnection exhausts. The largest values of E∥ are observed within double layers. The existence of double layers in the Earth's magnetosphere is well documented. In our simulation, their formation is triggered by large parallel streaming of Electrons into the reconnection region. These parallel Electron fluxes are required for maintaining quasi-neutrality of the reconnection region and increase with decreasing values of the normalized Electron Pressure upstream of the reconnection region, βe∞=2μ0ne∞Te∞/B∞2. A threshold (βe∞ < 0.02) is derived for strong double layers to develop. We also document how the Electron confinement, provided in part by the structure in E∥, allows sustained energization by perpendicular electric fields (E⊥). The energization is a consequence of the confined Electrons' chaotic orbital motion that includes drifts ali...
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a review of Pressure anisotropy caused by Electron trapping in collisionless plasma and its implications for magnetic reconnection
Physics of Plasmas, 2013Co-Authors: J Egedal, William DaughtonAbstract:From spacecraft data, it is evident that Electron Pressure anisotropy develops in collisionless plasmas. This is in contrast to the results of theoretical investigations, which suggest this anisotropy should be limited. Common for such theoretical studies is that the effects of Electron trapping are not included; simply speaking, Electron trapping is a non-linear effect and is, therefore, eliminated when utilizing the standard methods for linearizing the underlying kinetic equations. Here, we review our recent work on the anisotropy that develops when retaining the effects of Electron trapping. A general analytic model is derived for the Electron guiding center distribution f¯(v∥,v⊥) of an expanding flux tube. The model is consistent with anisotropic distributions observed by spacecraft, and is applied as a fluid closure yielding anisotropic equations of state for the parallel and perpendicular components (relative to the local magnetic field direction) of the Electron Pressure. In the context of reconnection, the new closure accounts for the strong Pressure anisotropy that develops in the reconnection regions. It is shown that for generic reconnection in a collisionless plasma nearly all thermal Electrons are trapped, and dominate the properties of the Electron fluid. A new numerical code is developed implementing the anisotropic closure within the standard two-fluid framework. The code accurately reproduces the detailed structure of the reconnection region observed in fully kinetic simulations. These results emphasize the important role of Pressure anisotropy for the reconnection process. In particular, for reconnection geometries characterized by small values of the normalized upstream Electron Pressure, βe∞, the Pressure anisotropy becomes large with p∥≫p⊥ and strong parallel electric fields develop in conjunction with this anisotropy. The parallel electric fields can be sustained over large spatial scales and, therefore, become important for Electron acceleration.
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regimes of the Electron diffusion region in magnetic reconnection
Physical Review Letters, 2013Co-Authors: A Le, J Egedal, O Ohia, Homa Karimabadi, William Daughton, V S LukinAbstract:: The Electron diffusion region during magnetic reconnection lies in different regimes depending on the Pressure anisotropy, which is regulated by the properties of thermal Electron orbits. In kinetic simulations at the weakest guide fields, pitch angle mixing in velocity space causes the outflow Electron Pressure to become nearly isotropic. Above a threshold guide field that depends on a range of parameters, including the normalized Electron Pressure and the ion-to-Electron mass ratio, Electron Pressure anisotropy develops in the exhaust and supports extended current layers. This new regime with Electron current sheets extending to the system size is also reproduced by fluid simulations with an anisotropic closure for the Electron Pressure. It offers an explanation for recent spacecraft observations.
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kinetic structure of the Electron diffusion region in antiparallel magnetic reconnection
Physical Review Letters, 2011Co-Authors: Jonathan Ng, J Egedal, A Le, William Daughton, L J ChenAbstract:Strong Electron Pressure anisotropy has been observed upstream of Electron diffusion regions during reconnection in Earth's magnetotail and kinetic simulations. For collisionless antiparallel reconnection, we find that the anisotropy drives the Electron current in the Electron diffusion region, and that this current is insensitive to the reconnection electric field. Reconstruction of the Electron distribution function within this region at enhanced resolutions reveals its highly structured nature and the mechanism by which the Pressure anisotropy sets the structure of the region.
Roderick Boswell - One of the best experts on this subject based on the ideXlab platform.
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Approaching the theoretical limit of diamagnetic-induced momentum in a rapidly diverging magnetic nozzle.
Physical review letters, 2013Co-Authors: Kazunori Takahashi, Christine Charles, Roderick BoswellAbstract:Cross-field diffusion and plasma expansion in a rapidly diverging magnetic nozzle are controlled while maintaining constant plasma production in a contiguously attached radio frequency plasma source. It is demonstrated that the measured Electron-diamagnetic-induced axial momentum increases with increasing magnetic field strength to approach the theoretical limit derived using an ideal nozzle approximation. The measured axial momentum exerted onto the axial and radial plasma source boundaries validate the prediction from a maximum Electron Pressure model on the back wall and from a zero net axial momentum model on the radial wall.
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direct thrust measurements and modelling of a radio frequency expanding plasma thruster
Physics of Plasmas, 2011Co-Authors: Trevor Lafleur, Kazunori Takahashi, Christine Charles, Roderick BoswellAbstract:It is shown analytically that the thrust from a simple plasma thruster (in the absence of a magnetic field) is given by the maximum upstream Electron Pressure, even if the plasma diverges downstream. Direct thrust measurements of a thruster are then performed using a pendulum thrust balance and a laser displacement sensor. A maximum thrust of about 2 mN is obtained at 700 W for a thruster length of 17.5 cm and a flow rate of 0.9 mg s−1, while a larger thrust of 4 mN is obtained at a similar power for a length of 9.5 cm and a flow rate of 1.65 mg s−1. The measured thrusts are in good agreement with the maximum upstream Electron Pressure found from measurements of the plasma parameters and in fair agreement with a simple global approach used to model the thruster.
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direct thrust measurement of a permanent magnet helicon double layer thruster
Applied Physics Letters, 2011Co-Authors: Kazunori Takahashi, Trevor Lafleur, P Alexander, Roderick Boswell, Marion Perren, Robert Laine, Sabrina Pottinger, Christine Charles, Vaios Lappas, Tania HarleAbstract:Direct thrust measurements of a permanent magnet helicon double layer thruster have been made using a pendulum thrust balance and a high sensitivity laser displacement sensor. At the low Pressures used (0.08 Pa) an ion beam is detected downstream of the thruster exit, and a maximum thrust force of about 3 mN is measured for argon with an rf input power of about 700 W. The measured thrust is proportional to the upstream plasma density and is in good agreement with the theoretical thrust based on the maximum upstream Electron Pressure.