Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh22a..08m&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #SH22A-08
Other
7839 Nonlinear Phenomena, 7843 Numerical Simulation Studies, 7851 Shock Waves, 2139 Interplanetary Shocks, 2154 Planetary Bow Shocks
Scientific paper
The electron dynamics within a shock ramp is investigated with the help of computer simulations. We consider a perpendicular geometry, where \hat x points into the shock, \hat z is the magnetic field direction, and the electric fields' structure is E=(Ex,E_y,0) with the motional field Ey= const. The magnetic ramp Bz(x) is modeled. In order to analyse the electron behaviour in this cross field structure, we first study test particle motion assuming an adhoc electrostatic potential φ (x) ~ Bz(x) with φ (x)=-∫ 0x Ex dx. In most cases, the electrons lose the kinetic energy they acquire by progressing in x as they Ex x Bz drift in the \hat y direction; their only gain results from the ∇ B component of their drift, which corresponds to conservation of the magnetic moment and adiabatic heating. On the other hand, we also recover the ``superadiabatic heating'' described by previous authors [Balikhin and Gedalin (1994); Ball and Galloway (1998)] for extreme cases where the gradient of the potential is so strong that electrons are accelerated across a large fraction of the ramp during their first gyration after entering the ramp. The required potential depends upon the ratio of electron cyclotron to plasma frequencies, namely eφ ~ D2 mc2 (Ω ce}/ω {pe)2 where D is the ramp's half width expressed in electron inertia length. We then turn to highly inhomogeneous PIC simulations of the ramp, and investigate the electron response to a potential generated selfconsistently through the partial decoupling of ions and electrons which takes place in a shock ramp. The incoming electrons, slowing down in the rising magnetic ramp, hold back the ions via the electrostatic field. Now, if the electrons are allowed to slip through, the ions are less contained and the whole ramp structure slides further. This questions the superadiabatic regime. We will discuss the interpretation of our simulations and will support it by means of several diagnostics.
Muschietti L.
Roth Ilan
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