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| Titel |
Electron heating via microturbulence occurring in the front of supercritical quasiperpendicular shocks |
| VerfasserIn |
L. Muschietti, B. Lembège |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063769
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| Zusammenfassung |
| In supercritical shocks, as well known, a certain fraction of the incoming ions are reflected at
the steep magnetic ramp, stream across the magnetic field and accumulate to form the foot.
The simultaneous presence of beams of incoming and reflected ions, and incoming
electrons leads to a microturbulence driven by their relative drifts. The waves easiest to
excite are in the electron cyclotron frequency range and generated by the electron
cyclotron drift instability [1]. Several Bernstein harmonics can be unstable, their
number being directly proportional to the drift of the reflected ion beam versus the
electrons. The number of harmonics and their level of intensity is limited, however,
linearly by the ion beam’s temperature and nonlinearly by resonance broadening
[2].
Electromagnetic PIC simulations restricted to the foot region are performed to investigate
the nonlinear characteristics of this microturbulence. The simulations, which are designed to
provide a high spatial resolution, are characterized by a large mass ratio value and a large
ratio of electron plasma to cyclotron frequency. While first, high cyclotron harmonics
develop in good agreement with linear dispersion properties, subsequently a nonlinear
dynamics similar to the inverse cascade takes place whereby the spectral power shifts
toward lower k-modes to eventually accumulate on the first harmonic branch with
frequency Ωce. We discuss the role played by resonance broadening in this inverse
cascade and show that the latter phase is characterized by the development of a
magnetic component to the spectrum and exhibits a significant energy transfer from the
reflected ion beam to the electrons, which experience a marked increase in their
temperature.
[1] L. Muschietti and B. Lembège, “Electron cyclotron microinstability in the foot of a
perpendicular shock: A self-consistent PIC simulation”, Adv. Space Res., 37, 2006, pp.
483–493.
[2] M. Lampe, W.M. Mannheimer, J.B. McBride, J.H. Orens, K. Papadopoulos, R.
Shanny, and R.N. Sudan, “Theory and Simulation of the Beam Cyclotron Instability”, Phys.
Fluids, 15, 1972, pp. 662–675. |
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