HR: 0800h
AN: SM51C-0389    [Abstracts]
TI: Electron Cyclotron Microinstability in the Foot of a Perpendicular Shock: a Self-consistent PIC Simulation
AU: * Muschietti, L
EM: laurent@ssl.berkeley.edu
AF: Space Sciences Laboratory University of California, 7 Gauss Way, Berkeley, CA 94720-7450 United States
AU: Lemb\`ege, B
EM: Bertrand.Lembege@cetp.ipsl.fr
AF: CETP-CNRS-UVSQ, 10--12 Avenue de l'Europe, Velizy, F-78140 France
AB: A few decades ago it was argued that the ions which are reflected in perpendicular supercritical shocks might excite various plasma microinstabilities within the shock's foot. Only now, thanks to advances in computational power, are we able to investigate them in a truly self-consistent way, where the instabilities are embedded within the larger frame of an evolving shock structure. With the help of a newly developed Darwin PIC code, we have identified an electron cyclotron microinstability that occurs during the reformation phase of strictly perpendicular shocks at low $\beta_i$. The instability involves the beam of reflected ions and the ambient electrons. It takes place within the foot itself, exhibits a rapid growth, and propagates along the shock normal towards upstream. Its frequency is comparable to the electron cyclotron frequency and its wavelength shorter than the electron inertia length. The instability basically results from the coupling of electron Bernstein waves with an ion beam mode carried by the reflected ions, whereby we identify it as a variety of the electron cyclotron drift instability [e.g. {\it Forslund et al.}, 1970]. A dispersion analysis is presented. We discuss the effects of varying parameters, in particular as the fake ion-to-electron mass ratio used in the simulations converges to more realistic values. The connection with the Buneman instability reported in the much higher Mach simulations of [{\it Shimada and Hoshino}, 2000] is outlined.
DE: 7839 Nonlinear phenomena
DE: 7843 Numerical simulation studies
DE: 7851 Shock waves
DE: 7899 General or miscellaneous
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting