Electron Cyclotron Waves in the Foot of a Supercritical Shock: Parametric Analysis
Abstract
Recent simulations of supercritical perpendicular shock [1] have evidenced an electron cyclotron drift instability (ECDI) within the shock's foot, which is excited by the relative drift between the beam of reflected ions and the incoming electrons. Herein that work is extended to a more realistic parameter regime (higher mass ratio and higher plasma to cyclotron frequency ratio) by means of 1D PIC simulations restricted to the foot. The much higher spatial resolution afforded by the present simulations enables us to study in exquisite detail the development of the instability. Main features are: (i) Cyclotron harmonics with high k ρe values and frequencies near the upper hybrid are excited in the linear stage, in good agreement with linear dispersion properties. (ii) As the orbits of the beam's ions in Cerenkov resonance with the waves become nonlinear, the high k modes are quenched letting lower harmonics grow. (iii) The resulting ion phase mixing, whereby the same ions resonate with different wavelengths, leads to a spectral shift from high to low k modes in a timescale on the order of the trapping time. That dynamics (which is distinct from vortex coalescence related to the inverse cascade process) leads to an accumulation of spectral power near the lowest cyclotron harmonics and a significant heating of the electrons. The dynamics is analysed for different ion beam drifts that represents different supercritical yet moderate Mach number regimes of shocks. [1] Muschietti L. and B. Lembege, Adv. Space Res. 37, 483 (2006)
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMSM51A1619M
- Keywords:
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- 7829 Kinetic waves and instabilities;
- 7839 Nonlinear phenomena (4400;
- 6944);
- 7851 Shock waves (4455);
- 7867 Wave/particle interactions (2483;
- 6984)