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P: Fachverband Plasmaphysik
P 17: Astrophysical Plasmas
P 17.5: Talk
Thursday, March 31, 2022, 15:00–15:15, P-H11
Pre-acceleration in the Electron Foreshock: Electron Acoustic Waves — •Paul Morris1, Artem Bohdan1, Martin Weidl3, and Martin Pohl1,2 — 1Deutsches Elektronen-Synchrotron DESY, Platanenallee 6, 15738 Zeuthen, Germany — 2Institute of Physics and Astronomy, University of Potsdam, D-14476 Potsdam, Germany — 3Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, DE-85748 Garching, Germany
To undergo diffusive shock acceleration, electrons need to be pre-accelerated to increase their energies by several orders of magnitude, else their gyro-radii are smaller than the finite width of the shock. In oblique shocks, electrons can escape to the shock upstream, creating a region called the electron foreshock. To determine the pre-acceleration in this region, we undertake PIC simulations of oblique shocks while varying the obliquity angle. We show that while the proportion of reflected electrons is negligible for θBn = 74.3∘, it increases to R ∼ 3% for θBn = 30∘, and that these electrons power electrostatic waves upstream with a wavelength around 2.5 λse, where λse is the electron skin length. While the initial reflection mechanism is a combination of shock surfing acceleration and magnetic mirroring, once the electrostatic waves have been generated upstream they themselves can increase the momenta of upstream electrons parallel to the magnetic field. In 1% of cases, upstream electrons are turned away from the shock and never injected downstream. In contrast, a similar fraction are re-directed back towards the shock after reflection and cross into the downstream.