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A Clash of Clusters Provides New Clue to Dark Matter
Special ACKS Seminar: Dragan Huterer
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ACKS Seminar: James Drake (University of Maryland; UC Berkeley)
| What | ACKS |
|---|---|
| When |
04 October 07 from 04:00 pm to 05:00 pm |
| Where | CAMPUS: Phys & Astrophys Bldg., 1st fl., conf rm (102/103) |
| Contact Name | Lukasz Stawarz |
| Contact Email | stawarz@slac.stanford.edu |
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Magnetic Reconnection and Particle Acceleration in Space and Astrophysics
Magnetic fields play a fundamental role in the dynamics of plasma systems, ranging from the solar corona to astrophysical accretion discs and jets. Observations indicate that the dissipation or release of magnetic energy occurs in explosive events, examples being solar and stellar flares, substorms in the Earth's magnetosphere, and disruptions in laboratory fusion experiments. The energy release occurs through magnetic reconnection, in which regions of oppositely directed magnetic field self-annihilate, converting magnetic free energy into high velocity flows, thermal energy and energetic particles. A suprisingly large fraction of the released energy appears in the form of energetic electrons -- up to 50% or more during solar flares. The mechanism for energetic electron and ion production during magnetic reconnection has remained a mystery. I will discuss the basic physics of reconnection before presenting new models of particle acceleration during reconnection. Observations and simulations suggest that magnetic energy dissipation during reconnection occurs in bath of contracting magnetic islands rather than in a single large-scale x-line. Electrons are efficiently accelerated through Fermi reflection in these islands. Ions gain energy through a pickup process in the high-speed outflow jets that result from reconnection. Solutions for energy spectra suggest that magnetic reconnection may be able to compete with high mach number shocks as an accelerator of cosmic rays. The talk will review key observational data and emphasize basic physical principles to introduce the topic to the non-specialist.
MASS: Lance Simms