1 / 34

The Structure of Thin Current Sheets Associated with Reconnection X-lines

The Structure of Thin Current Sheets Associated with Reconnection X-lines. Marc Swisdak The Second Workshop on Thin Current Sheets April 20, 2004. Collaborators. U. of Maryland. J. Drake M. Shay J. McIlhargey B. Rogers A. Zeiler. UMBC. Dartmouth College. MPP-Garching. z. y. x.

clare-bennett
Download Presentation

The Structure of Thin Current Sheets Associated with Reconnection X-lines

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Structure of Thin Current Sheets Associated with Reconnection X-lines Marc Swisdak The Second Workshop on Thin Current Sheets April 20, 2004

  2. Collaborators U. of Maryland • J. Drake • M. Shay • J. McIlhargey • B. Rogers • A. Zeiler UMBC Dartmouth College MPP-Garching

  3. z y x Simulation: J Bguide Breconn Reconnecting field: x Inflow velocity: y Guide field/Current: z

  4. p3d Details • Also: • 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

  5. The Point Q: At what strength does the guide field become important? A: Bg  0.1 B0

  6. No Guide Field: Overview

  7. Development of Bifurcation

  8. Temperature

  9. Velocity Distributions @ x-line: Beams are due to Speiser figure-8 orbits @ bifurcation: Multiple peaks from two beams

  10. Balancing the Reconnection Electric Field Ideal MHD Pressure tensor Electron Inertia

  11. Balancing the Reconnection Electric Field

  12. Guide Field: Bg=1B0 • Current sheet not bifurcated • Electrons magnetized at the x-line • Canted separtrices • E|| interacting with Bg

  13. Temperature, Bg=1

  14. Balancing the Reconnection Electric Field

  15. Guide Field Criterion • What is the minimum Bg so that the e- excursions are less than de? Reconnection Rate:

  16. X-line Structure: Bg = 0, 0.2, 1

  17. Temperature, Bg=0.2

  18. Off-Diagonal Pressure Tensor, Pyz

  19. X-line Distribution Functions Why is this important? Development of x-line turbulence. Why does it happen? Bg means longer acceleration times.

  20. 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

  21. Cut Through the X-line

  22. Reconnection Rate & Guide Field Reconnected Flux Time

  23. Tinit Tfinal Why the difference? Anti-parallel reconnection Within the diffusion region electrons are unmagnetized & execute wandering orbits. Guide field reconnection Electrons are always magnetized and are not heated.

  24. Generalized Ohm’s Law What terms does MHD neglect? The final three terms become important at different scales: di =c/wpi s, bedide Ideal MHD Hall term Electron Inertia Resistive MHD Pressure tensor

  25. 3D Reconnection with Guide Field

  26. ~J Electrons Ions Buneman Instability • Electron-ion two-stream instability. If the distribution functions do not (roughly) overlap then the system is unstable.

  27. 3D Reconnection w/o Guide Field early • Initial turbulence (LHDI) disappears as reconnection strengthens. • X-line shows no sign of instability at late times. late

  28. Temperature

  29. Temperature, Bg=0.2

  30. Temperature, Bg=1

  31. Dissipation mechanism • What balances Ep during guide field reconnection? • Scaling with electron Larmor scale suggests the non-gyrotropic pressure can balance Ep (Hesse, et al, 2002). Bz=0 Bz=1.0 y y

  32. Transition from anti-parallel to guide field reconnection • Structure of non-gyrotropic part of the pressure tensor, Pyz • Remove gyrotropic portion • Significant changes for Bz0=0.1 Bz0=0 Bz0=0.1 Bz0=1.0

More Related