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Plasma Physics (Physics/ECE/NE 922) Seminars

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Events During the Week of September 13th through September 20th, 2020

Monday, September 14th, 2020

Electron Scattering by Low-frequency Whistler Waves at Earth’s Bow Shock
Time: 12:00 pm
Place: VIRTUAL
Speaker: Mitsuo Oka, Scientist at Space Sciences Laboratory, University of California, Berkeley, CA, USA
Abstract: Electrons are accelerated to nonthermal energies at shocks in space and astrophysical environments. While shock drift acceleration (SDA) has been considered a key process of electron acceleration at Earth’s bow shock, it has also been recognized that SDA needs to be combined with an additional stochastic process to explain the observed power-law energy spectra. Here, we show mildly energetic (∼0.5 keV) electrons are locally scattered (and accelerated while being confined) by magnetosonic-whistler waves within the shock transition layer, especially when the shock angle is large (θ_Bn > 70 degrees). When measured by the Magnetospheric Multiscale mission at a high cadence, ∼0.5 keV electron flux increased exponentially in the shock transition layer. However, the flux profile was not entirely smooth and the fluctuation showed temporal/spectral association with large-amplitude ((δB/B ~ 0.3), low-frequency (<~ 0.1Ωce where Ωce is the cyclotron frequency), obliquely propagating (θ_kB ~ 30 − 60 degrees where θ_kB is the angle between the wave vector and background magnetic field) whistler waves, indicating that the particles were interacting with the waves. Particle simulations demonstrate that, although linear cyclotron resonances with ∼0.5 keV electrons are unlikely due to the obliquity and low frequencies of the waves, the electrons are still scattered beyond 90° pitch angle by coupled nonlinear scattering processes.

*** recurring Zoom meeting for the 922 Seminar in Plasma Physics. This will be valid all semester. The link is

https://uwmadison.zoom.us/j/99156107574?pwd=RnA0ZnJHbDdlOHN1dkpFYUVYcWZpUT09

The ID and passcode are:

Meeting ID: 991 5610 7574
Passcode: 883688
Host: Paul Terry
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Tuesday, September 15th, 2020

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Wednesday, September 16th, 2020

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Thursday, September 17th, 2020

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Friday, September 18th, 2020

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