Bulletin of the American Physical Society
57th Annual Meeting of the APS Division of Plasma Physics
Volume 60, Number 19
Monday–Friday, November 16–20, 2015; Savannah, Georgia
Session DI2: Reconnection from Lab to SpaceInvited
|
Hide Abstracts |
Chair: Paul Cassak, West Virginia University Room: Chatham Ballroom C |
Monday, November 16, 2015 3:00PM - 3:30PM |
DI2.00001: The Magnetospheric Multiscale Mission: New Data on Magnetic Reconnection Invited Speaker: James Burch The Magnetospheric Multiscale (MMS) mission was launched on March 12, 2015 into its Phase 1 elliptical orbit with apogee at 12 Earth radii (R$_{\mathrm{E}})$. The baseline science goal for MMS is to \textit{Understand the microphysics of magnetic reconnection by determining the kinetic processes occurring in the electron diffusion region that are responsible for collisionless magnetic reconnection, especially how reconnection is initiated. }In priority order, MMS will address three specific objectives: (1) Determine the role played by electron inertial effects and turbulent dissipation in driving magnetic reconnection in the electron diffusion region; (2) Determine the rate of magnetic reconnection and the parameters that control it. (3) Determine the role played by ion inertial effects in the physics of magnetic reconnection. During the six months of commissioning following launch, all of the instruments on the four spacecraft were made fully operational. Beginning on September 1, 2015 the spacecraft began their first scan of the dayside magnetopause in a tetrahedral formation with separations of 160 km. During Phase 1 the separation will be reduced in steps to 10 km and then adjusted to the separation that is judged to be optimum for reconnection studies. A second scan of the dayside magnetopause will be conducted at this optimum separation. Then apogee will be raised to 25 R$_{\mathrm{E}}$ for a scan of the magnetotail with separations variable from 30 km to 400 km. Throughout the mission the payload will be operated at its maximum data rate, which is sufficient to investigate reconnection down to approximately the electron diffusion length scale with full 3D plasma electron distributions obtained in 30 ms, ion distributions at 150 ms, and magnetic and electric fields at 1 ms resolution. 3D plasma and energetic ion composition an energetic electron measurements along with plasma waves will also be made. The spacecraft potential is maintained below $+$4V by an ion emitter. Because of the large amount of data and the downlink limitations, only a few per cent of data at the highest rates can be sent to the ground. An on-board data selection system, supplemented by a Scientist-in-the Loop (SITL) system will be used to obtain the best segments of high-rate data for reconnection studies. Results from the first three months of Phase 1 will be presented in this paper. [Preview Abstract] |
Monday, November 16, 2015 3:30PM - 4:00PM |
DI2.00002: Dynamics of a reconnection-driven runaway ion tail in a reversed field pinch plasma Invited Speaker: Jay Anderson Non-collisional heating and energization of ions is a powerful process in reversed-field pinch (RFP) plasmas and in many astrophysical settings. Tearing activity in the RFP (including linearly and nonlinearly driven modes which span the plasma column) saturates through dynamo-like feedback on the current density profile, rapidly releasing magnetic energy and inducing a strong impulsive, parallel-to-B electric field as poloidal magnetic flux is converted to toroidal flux. The global reconnection leads to strong ion heating with a known anisotropy in temperature ($T_\perp > T_{||}$), suggestive of a perpendicular bulk heating mechanism. In the subset of strongest reconnection events, multiple mechanisms combine to create a most interesting ion distribution. Runaway of the reduced-friction naturally-heated ions generates an asymmetric ion tail with $E_{||} >> E_\perp$. The tail is reinforced by a confinement asymmetry where runaway ions approach the limit of classical cross-field transport despite magnetic stochasticity from the broad spectrum of tearing modes. Confinement is lower in other regions of the $v_\perp/v_{||}$ plane and reduces to Rechester-Rosenbluth-like transport experienced by thermal particles. Experiments with neutral beam injection elegantly confirm the ion runaway process and fast ion confinement characteristics in MST. Neutral particle analyzers measure an unrestricted parallel acceleration of the fast test particle distribution during the reconnection event. The energy gain is larger for higher initial ion energy (reduced drag), and deceleration is observed with reversed electric field (counter-current injection) according to runaway dynamics and confirmed with Fokker-Planck modeling. Full orbit test particle tracing in the 3D time evolving electric and magnetic fields (from visco-resistive MHD simulations) corroborates the understanding of fast ion confinement. Work supported by by US DoE and NSF. [Preview Abstract] |
Monday, November 16, 2015 4:00PM - 4:30PM |
DI2.00003: Nonthermal Particle Acceleration and Radiation in Relativistic Magnetic Reconnection Invited Speaker: Gregory Werner Many spectacular and violent phenomena in the high-energy universe exhibit nonthermal radiation spectra, from which we infer power-law energy distributions of the radiating particles. Relativistic magnetic reconnection, recognized as a leading mechanism of nonthermal particle acceleration, can efficiently transfer magnetic energy to energetic particles. We present a comprehensive particle-in-cell study of particle acceleration in 2D relativistic reconnection in both electron-ion and pair plasmas without guide field. We map out the power-law index $\alpha$ and the high-energy cutoff of the electron energy spectrum as functions of three key parameters: the system size (and initial layer length)$~L$, the ambient plasma magnetization$~\sigma$, and the ion/electron mass ratio (from 1 to 1836). We identify the transition between small- and large-system regimes: for small$~L$, the system size affects the slope and extent of the high-energy spectrum, while for large enough$~L$, $\alpha$ and the cutoff energy are independent of $L$. We compare high energy particle spectra and radiative (synchrotron and inverse Compton) signatures of the electrons, for pair and electron-ion reconnection. The latter cases maintain highly relativistic electrons, but include a range of different magnetizations yielding sub- to highly-relativistic ions. Finally, we show how nonthermal acceleration and radiative signatures alter when the radiation back-reaction becomes important. These results have important implications for assessing the promise and the limitations of relativistic reconnection as an astrophysically-important particle acceleration mechanism. [Preview Abstract] |
Monday, November 16, 2015 4:30PM - 5:00PM |
DI2.00004: Magnetic Reconnection: A Powerful Cosmic Particle Accelerator Invited Speaker: Fan Guo Astrophysical magnetic reconnection sites have long been expected to be sources of high-energy particles. Recent observations of high-energy gamma-ray flares from the Crab nebula and hard X-ray emission from solar flares have motivated us to better understand magnetic reconnection and its associated particle acceleration in plasma conditions where the magnetic energy is dominant. We will present fully kinetic particle-in-cell simulations of anti-parallel magnetic reconnection in the highly magnetized regime (the magnetization parameter sigma \textgreater \textgreater 1 or plasma beta \textless \textless 1). The magnetic energy is converted efficiently into kinetic energy of nonthermal relativistic particles in a power-law spectrum.~For a sufficiently large system and strong magnetic field, the power-law index approaches ``-1''.~The dominant acceleration mechanism is a first-order Fermi process accomplished through the curvature drift motion of particles in magnetic flux tubes along the electric field induced by fast plasma flows. We will show simulations in three dimensions and with open boundary conditions. We will present an analytical model for the formation of power-law distribution and show the nonthermal distribution may be a common feature of magnetically dominated reconnection. Collaborators: Hui Li, William Daughton, Yi-Hsin Liu, Xiaocan Li References: Fan Guo, Hui Li, William Daughton, Yi-Hsin Liu (2014)~Formation of Hard Power-laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection, Physical Review Letters, 113, 155005 Yi-Hsin Liu, Fan Guo, William Daughton, Hui Li, Michael Hesse (2015)~Scaling of Magnetic Reconnection in Relativistic Collisionless Plasmas, Physical Review Letters, 114, 095002 Fan Guo, Yi-Hsin Liu, William Daughton, Hui Li (2015)~Particle Acceleration and Plasma Dynamics during Magnetic Reconnection in the Magnetically-dominated Regime, Astrophysical Journal 806, 167 Xiaocan Li, Fan Guo, Hui Li, Gang Li (2015) Nonthermally Dominated Electron Acceleration during Magnetic Reconnection in a Low-beta Plasma, ArXiv: 1505.02166 [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700