E2.3-0012-06

Electron Heating Mechanism in the Plasma SheetLobe Boundary Region Associated withMagnetic Reconnection

Keizo Fujimoto1 and Shinobu Machida2
1. Department of Physics, University of Alberta, Canada
2. Department of Geophysics, Kyoto University, Japan

Introduction
 Reaveling plasma acceleration and heating mechanism isvery important in understanding energy transport processes
associated with magnetic reconnection.
 Recent in-situ observations in theEarth magnetotail have showedthat a flat-topped electron
distribution is formed in theplasma sheet-lobe boundary region
associated with magneticreconnection. [Saito et al., 1995;
Shinohara et al., 1998; Hoshino etal., 2001][Shinohara et al., 1998]~ A few keV
36th COSPAR Scientific AssemblyIntroduction
 Suggesting mechanisms for the electron heating are,z Slow-mode shock [Schwartz et al., 1987; Saito et al., 1995]z Lower hybrid drift instability (LHDI) [Huba et al., 1978;
Shinohara et al., 1998]z Buneman or Bump-on-tail instabilities [Hoshino et al., 2001;
Drake et al., 2003]

However, the nature of the instabilities is not yet specified
because of low space-time resolution of satellite observations
and limited computer resources.

36th COSPAR Scientific AssemblyElectromagnetic Particle Simulation with AMR Technique
AMR techniqueParticle splitting algorithm∆r = ∆L/N1/2

N: Number of particles in the cell.

x1,2 = x0 ± ∆r; x3,4 = x0
y1,2 = y0; y3,4 = y0 ± ∆r
V1,2,3,4 = V0;
q1,2,3,4 = q0/4;
m1,2,3,4 = m0/4

36th COSPAR Scientific AssemblyLarge-Scale Simulations of Magnetic Reconnection
System size：Lx×Lz = 122.9λi ×30.7λi (Maximum resolution： 8192× 2048)
Boundary conditions：Periodic boundaries in x, conducting walls in z.
ΔLB = 0.12λi, Δt = 0.0008 ωci-1
Number of layers: 4Refinement criteria： Electron Debye length （Δ > 2λDe ）,Electron bulk velocity （Vey > 2.0 VA）,
Electron current density（ (jex2+jez2)1/2 > 0.5 enpsVA ）[Initial conditions]Harris-type current sheet [Harris, 1962]
mi/me = 100, Ti,ps/Te,ps = 8, c/VA = 16.7
λ= 0.5 λi, nb = 0.04 nps,
Number of cells 〜 6.4×105, Number of particles 〜 2.1× 107

36th COSPAR Scientific AssemblyWave Activity in Lobe-Sheet Boundary Region

36th COSPAR Scientific AssemblyElectron Heating

Electrons arescattered bythe waves
along field line.

36th COSPAR Scientific AssemblyResponsible Instability ModeZ = -1.3 λiElectron2-Stream(nb/n0=0.4)

Buneman(nb/n0=0.3)

Electron two-stream instability
is responsible for the wave activity.
36th COSPAR Scientific AssemblyOrigin of the Electron Beam

Hot electrons
heated quite
near the X-line.

Cold electrons
in the opposite
side of theplasma sheet.

36th COSPAR Scientific AssemblyGeneration of ESW¾ Electrostatic Solitary Waves (ESW) havebeen often observed in the PSBL of theEarth magnetotail. [e.g., Matsumoto et al.,
1994; Kojima et al., 1994]¾ It is suggested that the ESW result from
nonlinear evolutions of the electron 2stream instability. [Matsumoto et al., 1994;
Omura et al., 1996] 。
¾ However, it is not clear how the intenseelectron beams are produced.
Our simulation results indicate that magnetic
reconnection can be a significant candidate toproduce the electron beams which areresponsible for the generation of ESW.

36th COSPAR Scientific AssemblySummary and Conclusions
We studied electron heating mechanism in the plasma sheet-lobe boundary
region associated with magnetic reconnection. We used a newly developed
electromagnetic full particle code with AMR technique.
We found that the electron 2-stream instability is excited between thebackground (lobe) cold electrons and the intense beam electrons with highperpendicular temperature. Electrons are scattered and heated along thefield line and the flat-topped electron distribution is formed.
We have also revealed that the ESW are evolved from the electron 2-stream
instability associated with magnetic reconnection.
Thus, the electron 2-stream instability is responsible not only for theformation of the flat-topped electron distribution, but also for the generationof the ESW associated with magnetic reconnection.
36th COSPAR Scientific AssemblyFurther Study
Heating due to Slow-mode Shock
We could not find any clear structure of the slow-mode shocks in thepresent simulations. Much larger-scale simulations lasting for longer time
would be necessary for generation of the slow-mode shocks. [e.g., Arznerand Scholer, 2001]。

Heating due to the LHDI
Growth rate of LHDI： γLH 〜 0.1 ωLH = (ωci ωce)1/2
Growth rate of electron 2-stream inst.： γTS 〜 0.1 ωpeThis leads to γLH 〜 (me/mi)1/2 γTS, so that the electron 2-stream instability
can be excited much easily and affect more the electron heating. It isnecessary to perform 3-D simulations to see this.

36th COSPAR Scientific Assembly