HR: 17:25h
AN: SH22C-06    [PDF]
TI: Electron Dynamics in Perpendicular Shocks
AU: * Muschietti, L
EM: laurent@ssl.berkeley.edu
AF: Space Sciences Laboratory\\ UC Berkeley, 7 Gauss Way, Berkeley, CA 94720-7450 United States
AU: Roth, I
EM: ilan@ssl.berkeley.edu
AF: Space Sciences Laboratory\\ UC Berkeley, 7 Gauss Way, Berkeley, CA 94720-7450 United States
AB: A full particle electromagnetic code in the Darwin approximation is used to investigate the dynamics of the electrons in a fast magnetosonic shock. We assume a perpendicular geometry where x points into the shock and the electromagnetic field structure is ${\bf E}=(E_x,E_y,0)$ and ${\bf B}=(0,0,B_z)$. The 1D3V code has open boundaries with upstream and downstream particles traversing the left and right boundaries, respectively, while the shock structure remains in the simulation box. Two shock strengths are considered, including a near critical shock with alfvenic Mach number $M_a\sim 2$ and a supercritical shock with $M_a\sim 3$--$4$. The simulation is initiated by loading the particles according to profiles modeled from conservation laws (Rankine-Hugoniot). Particles and fields are then left to evolve and, once the ion dynamics develops, a self-consistent shock structure forms. Importantly, due to the partial decoupling of ions and electrons which occurs in the magnetic ramp, the electrostatic field $E_x$ builds up a large spike whose role is to slow down the ions. In the supercritical case a significant fraction of ions are reflected and accumulate in the foot, which leads to the process of cyclical shock reformation. We record the trajectories of selected electrons in order to analyse their behavior in the cross field structure of the ramp. We specially look for a possible ``superadiabatic heating'', a process described by previous authors [Balikhin and Gedalin (1994); Ball and Galloway (1998)]. The latter is expected to occur for extreme cases where the gradient of the electrostatic potential, which reflects the ions, is so strong that the electrons are accelerated across a large fraction of the ramp during one cyclotron gyration. The required potential difference across the ramp $\delta\phi^*$ depends upon its half width $\Delta$, namely ${e\delta\phi^*/mv_e^2}\approx (0.2/\beta_e)~(\Delta/\lambda_e)^2(r+1)^2$. Here, $\lambda_e$ is the electron inertia length $c/\omega_{pe}$ and $r$ is the compression ratio. Our study improves upon the above mentioned works in the sense that we use profiles of the electromagnetic fields that are self-consistently built instead of just adhoc profiles.
DE: 2154 Planetary bow shocks
DE: 7843 Numerical simulation studies
DE: 7851 Shock waves
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting