ParticleinCell Simulations of Magnetic Reconnection in Collisionless ForceFree Current Sheets
Magnetic reconnection is one of the most fundamental physical processes in plasmas. It is especially important for activity processes in space and astrophysical plasmas. We investigate magnetic reconnection in collisionless plasmas, focussing on current sheet configurations for which the current density is parallel to the magnetic field, i.e. forcefree current sheets.
We study the stability and dynamics of the forcefree Harris sheet, for which an exact equilibrium distribution function is known
(Harrison and Neukirch, 2009  below). The forcefree Harris sheet has fundamentally different physical properties than the standard Harris sheet with or without guide field. In particular, for the forcefree Harris sheet the plasma density and pressure are constant, whereas the mean velocity of the particle species varies with position. Furthermore, it has been shown that the distribution function of the forcefree Harris sheet can have unusual structures in velocity space
(Neukirch et al., 2009  below). We use particleincell (PIC) simulations to study the nonlinear evolution of the forcefree Harris sheet when it undergoes magnetic reconnection
(see Figure 1  below). We intend to study in particular the transition between guidefield reconnection and antiparallel reconnection, which is expected to happen during the reconnection process of the forcefree Harris sheet. We plan to compare the results for the forcefree Harris sheet with simulations of the normal Harris sheet with guide field.
Figure 1: Snapshots of a PIC simulation of magnetic reconnection in a forcefree Harris sheet. The figures show the magnetic field lines projected onto the xzplane (white) and the ycomponent of the current density (colour contours). This particular simulation uses a total of 1.5 x 10^{9} particles, with a proton to electron mass ratio of 4. The times shown are in units of the (inverse) ion cyclotron frequency and the length scales are in units of the ion inertial length.
References:
 M. G. Harrison and
T. Neukirch,
A onedimensional VlasovMaxwell equilibrium for the forcefree Harris sheet,
Physical Review Letters,
102, 1350031  1350034 (2009).

T. Neukirch, F. Wilson and M. G. Harrison,
A detailed investigation of the properties of a VlasovMaxwell equilibrium for the forcefree Harris sheet,
Physics of Plasmas,
16, 1221021  12210210 (2009).