Marc Swisdak The Second Workshop on Thin Current Sheets April 20, 2004 The Structure of Thin Current Sheets Associated with Reconnection X-lines Marc Swisdak The Second Workshop on Thin Current Sheets April 20, 2004
Collaborators J. Drake U. of Maryland M. Shay J. McIlhargey B. Rogers A. Zeiler U. of Maryland UMBC Dartmouth College MPP-Garching
z y Simulation: x J Bguide Breconn Reconnecting field: x Inflow velocity: y Guide field/Current: z
p3d Details Also: Relativistic PIC code Double Harris sheet Periodic BCs Relativistic PIC code Boris algorithm for particles Trapezoidal leapfrog for fields Multigrid for Poisson’s equation MPI parallelization Biggest runs: 512x256x256 2048 processors ~109 particles How we cheat: me/mi large c/cA small
The Point Q: At what strength does the guide field become important? A: Bg 0.1 B0
No Guide Field: Overview
Development of Bifurcation
Temperature
Velocity Distributions @ x-line: Beams are due to Speiser figure-8 orbits @ bifurcation: Multiple peaks from two beams
Balancing the Reconnection Electric Field Ideal MHD Pressure tensor Electron Inertia
Balancing the Reconnection Electric Field
Guide Field: Bg=1B0 Current sheet not bifurcated Electrons magnetized at the x-line Canted separtrices E|| interacting with Bg
Temperature, Bg=1
Balancing the Reconnection Electric Field
Guide Field Criterion What is the minimum Bg so that the e- excursions are less than de? Reconnection Rate:
X-line Structure: Bg = 0, 0.2, 1
Temperature, Bg=0.2
Off-Diagonal Pressure Tensor, Pyz
X-line Distribution Functions Why is this important? Development of x-line turbulence. Why does it happen? Bg means longer acceleration times.
Conclusions Bg ~ 0.1B0 is enough to influence the structure of x-lines. Affects: Flow geometries, separatrices, particle orbits (temperatures), particle energization, development of turbulence (?) Doesn’t affect: Reconnection rate, breaking of frozen-in condition Implication: Anti-parallel reconnection is rare in real systems. Most reconnection is component reconnection