1. Role of trapped electrons in pic-code simulations of reconnection J Egedal, MIT, PSFC, Cambridge, MA Thanks to W Daughton & J F Drake

2. Fluid description Navier Stoke’s equations for the electron fluid  Generalized Ohms law:

3. Pic-code simulation (by Prof. W Daughton) Why is J || limited to this small region? Works, but no equation for j || !

4. Trapped electron in simulation by Prof. W Daughton

5. M. Øieroset et al. Nature 412, (2001) M. Øieroset et al. PRL 89, (2002) Wind spacecraft observations in distant magnetotail, 60R E Measurements within the ion diffusion region reveal: Strong anisotropy in f e.

6. Applying f(x 0,v 0 ) = f  (|v 1 |) to an X-line geometry consistent with the Wind measurements A potential,   needed for trapping at low energies Wind data  Thermal electrons trapped   ~ -300V   ~ -700V   ~ -1000V TheoryWind J. Egedal et al., (2005) Phys. Rev. Lett. 94, 025006 + + + + +

7. Numerical simulation (by Prof. J. Drake) EyEy x/d i z/d i 026 0 9 0 0.8 -0.8 JyJy x/d i z/d i 026 0 9 0 en 0 v th,e  xz (E xz = -  xz ) x/d i z/d i 026 0 9 1.5 (=6T e ) Mass ratio: 225, T e =T i =0.25, B g =0.5B 0 Why is Jy limited to this small region?

8. Numerical simulation (by Prof. J. Drake)  || (E || = -  || ) x/d i z/d i 026 0 9 1.5 (=6T e ) 0 EyEy x/d i z/d i 026 0 9 0 0.8 -0.8 JyJy x/d i z/d i 026 0 9 0 en 0 v th,e x/d i z/d i 026 0 9 1.5 (=6T e )  xz (E xz = -  xz ) Mass ratio: 225, T e =T i =0.25, B g =0.5B 0  || (E || = -  || ) x/d i z/d i 026 0 9 1.5 (=6T e ) 0 Escape Energy = 6 Te

9. x/d i z/d i 026 0 9 0 1.5 Trajectories of thermal electrons  || (E || = -  || ) Representative electron orbits J || is carried by shifting electron orbits. The shift is controlled by the ions, required for quasi neutrality.