The rate of reconnection characterizes how quickly flux and mass can move into and out of the rec... more The rate of reconnection characterizes how quickly flux and mass can move into and out of the reconnection region. In the Terrestrial Reconnection EXperiment (TREX), the rate at which the antiparallel asymmetric reconnection occurs is modulated by the presence of a shock and a region of flux pileup in the high-density inflow. Simulations utilizing a generalized Harris-sheet geometry have tentatively shown agreement with TREX's measured reconnection rate scaling relative to system size, which is indicative of the transition from ion-coupled toward electron-only reconnection. Here, we present simulations tailored to reproduce the specific TREX geometry, which confirm both the reconnection rate scale and the shock jump conditions previously characterized experimentally in TREX. The simulations also establish an interplay between the reconnection layer and the Alfvénic expansions of the background plasma associated with the energization of the TREX drive coils; this interplay has no...
• The structure of the electron diffusion region is important to reconnection in space plasma • T... more • The structure of the electron diffusion region is important to reconnection in space plasma • The widths of laboratory electron reconnection layers match those of kinetic simulations • Kinetic simulations show that the electron pressure tensor breaks the electron frozen flux condition
Bulletin of the American Physical Society, Oct 25, 2017
Wisconsin-Madison-Kinetic effects are expected to dominate the collisionless reconnection regime,... more Wisconsin-Madison-Kinetic effects are expected to dominate the collisionless reconnection regime, where the mean free path is large enough that the anisotropic electron pressure can develop without being damped away by collisional pitch angle scattering. In simulations, the anisotropic pressure drives the formation of outflow jets [1]. These jets are expected to play a role in the reconnection layer at the Earth's magnetopause, which is currently being explored by Magnetospheric Multiscale Mission (MMS) [2]. Until recently, this regime of anisotropic pressure was inaccessible by laboratory experiments, but new data from the Terrestrial Reconnection Experiment (TREX) shows that fully collisionless reconnection can now be achieved in the laboratory. Future runs at TREX will delve deeper into this collisionless regime in both the antiparallel and guide-field cases. [1] Le, A. et al. JPP, 81(1).
layer formation [1]. A multi-tip version of the M-probe of Shadman [2], containing 32 Langmuir pr... more layer formation [1]. A multi-tip version of the M-probe of Shadman [2], containing 32 Langmuir probe tips and two magnetic coils, measures this anisotropy. Each tip is biased to a different potential, simultaneously measuring discrete parts of the I-V characteristic. Pulsing the coil locally increases the magnetic field near the tips, inducing a magnetic mirror force to reflect electrons with large values of v ⊥ /v. The change in velocity modifies the I-V characteristic and can be used to infer p ∥ /p ⊥. Results and analysis from the probe are presented. [1] J. Egedal et al., Nature Phys. (2012). [2] K. Shadman, Phys. Plasmas (2004).
Submitted for the DPP15 Meeting of The American Physical Society Accessing the new collisionless ... more Submitted for the DPP15 Meeting of The American Physical Society Accessing the new collisionless reconnection regime in laboratory experiment 1 JOSEPH OLSON, JAN EGEDAL, SAMUEL GREESS, JOHN WALLACE, MICHAEL CLARK, CARY FOREST, UW-Madison-The Terrestrial Reconnection Experiment (TREX), the largest dedicated reconnection experiment to date, is currently in operation at the Wisconsin Plasma Astrophysics Laboratory (WiPAL). In its inaugural run, TREX demonstrated its ability to operate in what has traditionally been called the collisionless reconnection regime by observing the out-of-plane magnetic field characteristic of Hall reconnection. Additionally, TREX is projected to access even more collisionless parameters in which electron pressure anisotropy develops, greatly influencing the dynamics of the reconnection process beyond two fluid effects [1]. For example, spacecraft observations [2] and kinetic simulations [3] show that large-scale current layers are driven by this pressure anisotropy. In the last year, TREX has undergone upgrades to its plasma heating, reconnection drive, and diagnostic suite in order to study these features exclusive to truly collisionless reconnection. Preliminary results from the newly optimized experimental runs will be presented.
The rate of reconnection characterizes how quickly flux and mass can move into and out of the rec... more The rate of reconnection characterizes how quickly flux and mass can move into and out of the reconnection region. In the Terrestrial Reconnection EXperiment (TREX), the rate at which the antiparallel asymmetric reconnection occurs is modulated by the presence of a shock and a region of flux pileup in the high-density inflow. Simulations utilizing a generalized Harris-sheet geometry have tentatively shown agreement with TREX's measured reconnection rate scaling relative to system size, which is indicative of the transition from ion-coupled toward electron-only reconnection. Here, we present simulations tailored to reproduce the specific TREX geometry, which confirm both the reconnection rate scale and the shock jump conditions previously characterized experimentally in TREX. The simulations also establish an interplay between the reconnection layer and the Alfvénic expansions of the background plasma associated with the energization of the TREX drive coils; this interplay has no...
• The structure of the electron diffusion region is important to reconnection in space plasma • T... more • The structure of the electron diffusion region is important to reconnection in space plasma • The widths of laboratory electron reconnection layers match those of kinetic simulations • Kinetic simulations show that the electron pressure tensor breaks the electron frozen flux condition
Bulletin of the American Physical Society, Oct 25, 2017
Wisconsin-Madison-Kinetic effects are expected to dominate the collisionless reconnection regime,... more Wisconsin-Madison-Kinetic effects are expected to dominate the collisionless reconnection regime, where the mean free path is large enough that the anisotropic electron pressure can develop without being damped away by collisional pitch angle scattering. In simulations, the anisotropic pressure drives the formation of outflow jets [1]. These jets are expected to play a role in the reconnection layer at the Earth's magnetopause, which is currently being explored by Magnetospheric Multiscale Mission (MMS) [2]. Until recently, this regime of anisotropic pressure was inaccessible by laboratory experiments, but new data from the Terrestrial Reconnection Experiment (TREX) shows that fully collisionless reconnection can now be achieved in the laboratory. Future runs at TREX will delve deeper into this collisionless regime in both the antiparallel and guide-field cases. [1] Le, A. et al. JPP, 81(1).
layer formation [1]. A multi-tip version of the M-probe of Shadman [2], containing 32 Langmuir pr... more layer formation [1]. A multi-tip version of the M-probe of Shadman [2], containing 32 Langmuir probe tips and two magnetic coils, measures this anisotropy. Each tip is biased to a different potential, simultaneously measuring discrete parts of the I-V characteristic. Pulsing the coil locally increases the magnetic field near the tips, inducing a magnetic mirror force to reflect electrons with large values of v ⊥ /v. The change in velocity modifies the I-V characteristic and can be used to infer p ∥ /p ⊥. Results and analysis from the probe are presented. [1] J. Egedal et al., Nature Phys. (2012). [2] K. Shadman, Phys. Plasmas (2004).
Submitted for the DPP15 Meeting of The American Physical Society Accessing the new collisionless ... more Submitted for the DPP15 Meeting of The American Physical Society Accessing the new collisionless reconnection regime in laboratory experiment 1 JOSEPH OLSON, JAN EGEDAL, SAMUEL GREESS, JOHN WALLACE, MICHAEL CLARK, CARY FOREST, UW-Madison-The Terrestrial Reconnection Experiment (TREX), the largest dedicated reconnection experiment to date, is currently in operation at the Wisconsin Plasma Astrophysics Laboratory (WiPAL). In its inaugural run, TREX demonstrated its ability to operate in what has traditionally been called the collisionless reconnection regime by observing the out-of-plane magnetic field characteristic of Hall reconnection. Additionally, TREX is projected to access even more collisionless parameters in which electron pressure anisotropy develops, greatly influencing the dynamics of the reconnection process beyond two fluid effects [1]. For example, spacecraft observations [2] and kinetic simulations [3] show that large-scale current layers are driven by this pressure anisotropy. In the last year, TREX has undergone upgrades to its plasma heating, reconnection drive, and diagnostic suite in order to study these features exclusive to truly collisionless reconnection. Preliminary results from the newly optimized experimental runs will be presented.
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Papers by Samuel Greess