Post on 15-Jan-2016
Role of trapped electrons in pic-code simulations of reconnection
J Egedal,
MIT, PSFC, Cambridge, MA
Thanks to W Daughton & J F Drake
Fluid descriptionNavier Stoke’s equations for the electron fluid
)()( eeeeee t
nmne
v
vvpj B vE
Generalized Ohms law:)( eii vvj, vv ne
)()(12 tne
mne
ee
j jvpBjj B vE
|||| jvbEb 2
1nem
pne
e
b
Pic-code simulation (by Prof. W Daughton)
Why is J|| limited to this small region?
|||| jvbEb 2
1nem
pne
e
Works, but no equation for j||!
Trapped electron in simulation by Prof. W Daughton
M. Øieroset et al. Nature 412, (2001)
M. Øieroset et al. PRL 89, (2002)
Wind spacecraft observations in distant magnetotail, 60RE
• Measurements within the ion diffusion region reveal: Strong anisotropy in fe.
• Applying f(x0,v0) = f(|v1|) 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
Theory Wind
J. Egedal et al., (2005) Phys. Rev. Lett. 94, 025006
+ ++ ++
Numerical simulation (by Prof. J. Drake)
Ey
x/di
z/di
0 260
9
0
0.8
-0.8
Jy
x/di
z/di
0 260
9
0
en0vth,e xz (Exz= -xz)
x/di
z/di
0 260
9 1.5 (=6Te)
-1.0
Mass ratio: 225, Te=Ti=0.25, Bg=0.5B0
Why is Jy limited to this small region?
Numerical simulation (by Prof. J. Drake)
|| (E||= -||)
x/di
z/di
0 260
9 1.5 (=6Te)
0
Ey
x/di
z/di
0 260
9
0
0.8
-0.8
Jy
x/di
z/di
0 260
9
0
en0vth,e
x/di
z/di
0 260
9 1.5 (=6Te)
-1.0
xz (Exz= -xz)
Mass ratio: 225, Te=Ti=0.25, Bg=0.5B0
|| (E||= -||)
x/di
z/di
0 26
0
91.5 (=6Te)
0
Escape Energy = 6 Te
x/di
z/di
0 26
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.