PARTICLE-IN-CELL SIMULATIONS OF FAST MAGNETIC-FIELD PENETRATION INTO PLASMAS DUE TO THE HALL ELECTRIC-FIELD

Particle-in-cell (PIC) simulations are used to study the penetration o f magnetic field into plasmas in the electron-magnetohydrodynamic (EMH D) regime. These simulations represent the first definitive verificati on of EMHD with a PIC code. When ions are immobile, the PIC results re produce many aspects of fluid treatments of the problem. However, the PIC results show a speed of penetration that is between 10% and 50% sl ower than predicted by one-dimensional fluid treatments. In addition, the PIC simulations show the formation of vortices in the electron flo w behind the EMHD shock front. The size of these vortices is on the or der of the collisionless electron skin depth and is closely coupled to the effects of electron inertia. An energy analysis shows that one-ha lf the energy entering the plasma is stored as magnetic field energy w hile the other half is shared between internal plasma energy (thermal motion and electron vortices) and electron kinetic energy loss from th e volume to tile boundaries. The amount of internal plasma energy satu rates after an initial transient phase so that late in time tile rate that magnetic energy increases in the plasma is the same as the rate a t which kinetic energy flows out through the boundaries. When ions are mobile it is observed that axial magnetic field penetration is follow ed by localized thinning in the ion density. The density thinning is p roduced by the large electrostatic fields that exist inside the electr on vortices which act to reduce the space-charge imbalance necessary t o support the vortices. This mechanism may play a role during the open ing process of a plasma opening switch. (C) 1996 American Institute of Physics.