Michael Harrison Thomas Neukirch Michael Hesse 5th Cambridge Workshop on Magnetic Reconnection Bad Honnef August 17-22, 2008 A Comparison of 2D PIC simulations of Reconnection
Motivation • To compare the reconnection process using 2.5D PIC simulations starting from different initial conditions. • To investigate the morphology of the off-diagonal components of the electron pressure tensor as you go from weak to strong guide field using 2.5D PIC simulations to compare to previous results. • To investigate this transition using Vlasov-Maxwell equilibria resulting from distribution functions that extend beyond the Harris sheet. • To include in the investigation a comparison to the reconnection process starting from a self-consistent force-free Vlasov-Maxwell equilibria. • Currently we carry out our simulations with mass ratio = 1
The Structure of the Diffusion Region • The electron equation of motion • The y component of the electric field can be written as • Is found that the gradients of the off-diagonal terms of the pressure tensor are the dominant contributions to at the X-Point (Hesse 1999, 2001, Pritchett 2001, etc.).
Harris Sheet Cases Flux Normalised Reconnection Rate Reconnected Flux movies\harriscxz.mpg movies\harrisby05cxz.mpg movies\harrisby1cxz.mpg
Pressure Tensor Component Comparisons movies\harrisby05pxye.mp4 movies\harrispxye.mp4 movies\harrisby1pxye.mp4
Pressure Tensor Component Comparisons movies\harrispyze.mp4 movies\harrisby05pyze.mp4 movies\harrisby1pyze.mp4
Anisotropic Bi-Maxwellian Distribution Function • Have to find periodic solutions of the differential equations. • The case gives anti-parallel field configuration – • The case gives linear force-free equilibrium (Bobrova et al. 2001) • Can use the parameter to vary the shear field while keeping constant • Can investigate the transition from a pressure balanced equilibrium to a force-free equilibrium.
The Two Cases Numerical Solution
Anisotropic Bi-Maxwellian Cases Flux Normalised Reconnection Rate Reconnected Flux movies\onlypy2cxz.mpg movies\onlypy2by05cxz.mpg movies\onlypy2by1cxz.mpg movies\bobcxz.mpg
Pressure Tensor Component Comparisons movies\onlypy2pxye.mp4 movies\onlypy2by05pxye.mp4 Force-Free movies\onlypy2by1pxye.mp4 movies\bobpxye.mp4
Pressure Tensor Component Comparisons movies\onlypy2pyze.mp4 movies\onlypy2by05pyze.mp4 Force-Free movies\onlypy2by1pyze.mp4 movies\bobpyze.mp4
Conclusions • We have investigated the morphology of the off-diagonal components of the electron pressure tensor as you make the transition from an initial condition with a weak guide field through to a strong guide field including a linear force-free initial configuration. • In the initial stages of reconnection the structure of the electron pressure tensor components are similar for all initial conditions when compared to the previously known Harris sheet cases. • It can be seen that in the case of the periodic equilibria resulting from an anisotropic bi-Maxwellian distribution function the structure of the electron pressure tensor components are drastically changed in the latter stages due to interaction of the multiple current sheets. • The evolution of the periodic equilibria results in an almost complete change in the geometry of the field from initially having a structure to having a structure at the end.