Lower-Hybrid Drift Instability (LHDI)

Summary and Simulation Results

x y

BJ=μ0

-1 rot B

x-z: reconnection plane

z

y-z: current sheet plane

Summary of LHDI

Magnetic Reconnectionand instabilities in current sheet

• The LHDI is driven by the diamagnetic current in the presence of inhomogeneities in the density and magnetic field

• Fastest growing modes

2 2 1/ 2

2

0, 1, ,

/(1 / ) ,

, ( / ) 1, .

y e y i lh lh

lh pi pe ce

pe ce lh ce ci

k B k k U

Given

Summary of LHDI

• Historically, LHDI has attracted much attention in as a source of anomalously large resistivity observed in laboratory device.

• Subsequently and quite naturally, LHDI was suggested as a source of anomalous resistivity in the magnetotail.

Summary of LHDI

• Nonlinear phase of instabilities in the current sheet and their contribution to the reconnection cannot fully understood except by means of simulations.

• However, …

Simulation of LHDI Early Results

Current computer simulations face many practical hurdles indealing with realistic situation, e.g. The difficulty of implementingthe realistic proton-to-electron mass ratio. Besides, it is difficultto use the simulations carried out under highly idealized situationsand extrapolate to the real situations.

Simulation of LHDI Early Results

Winske [Phys. Fluids 1981] describe a longer wavelength EM mode which develops in the central region after the saturation of fastest growing LHDI. Characteristic wave vector:

Tanaka [J. Geophys. Res. 1981]

0.85y i ek

/ 0.6y ik U

• Despite earlier suggestion that LHDI may play a key role in magnetotail reconnection physics, it was soon realized that LHDI is stabilized as a result of increasing local beta.

• However, efforts were made to show that LHDI is not completely stabilized near the neutral sheet in a magnetotail-like geometry.

Summary of LHDI

Daughton 2003 Phys. Plasmas

1. Fastest growing modes:

ES waves are confined to the edge of sheet 0.5<|x/L|<3.5.

Bzw 0.5 <|x/L|<2..5

Note: For a given wavelength, there are actually multiple unstable lower-hybrid modes.

Simulation of LHDI Recent Results

Daughton [Phys. Plasmas 2003]/ 2, / 512,

/ 5, / 1i i e

pe ce i e

L m m

T T

/ 1i L

Daughton 2003 Phys. Plasmas

2. Long wavelength modes

ES waves are still confined to the edge

EM waves are localized about the center. γ/Ωci=0.84

Note: For a given wavelength, there are actually multiple unstable lower-hybrid modes.

Simulation of LHDI Recent Results

Simulation of LHDI Recent Results

Fastest growing LHDI have saturatedES waves are confined to the edge of sheet.Bz 0.5<|x/L|<1.0Ey 0.5<|x/L|<4.0

Simulation of LHDI Recent Results

USTC School of Earth and Space Sci.

• 对电流剖面的影响：对不同厚度的电流片，可形成中心增强的电流片以及双峰电流片。

• 对电子的加热：低混杂漂移不稳定性加热电子，并造成温度各项异性，垂直磁场方向温度大于平行电场温度。

0.915i

L

1.828i

L

Ricci 2005 Phys. Plasmas

1.828i

L

0.915i

L

Simulation of LHDI Recent Results

USTC School of Earth and Space Sci.

/y s y s yp m v q A c

Daughton 2004 PRL

vy

vz

U i

ky

U i

2

Noncrossing

Crossing

Crossing

Example of scattering

Lower-hybrid fluctuations

0 ln[cosh( / )]yA B L z L

2 2crossing / 2 , noncrossing / 2y s y sp m p m 21

( )2 2

y z

ths ths

v v

v v

( / ) ln[cosh( / )]sL z L

2 2( ) / 2s z ym v v

Simulation of LHDI Recent Results

LHDI(electron scale)

1y ek

CSKI(hybrid scale)

1y i ek

1y ik

KHI(MHD scale)

Shinohara 2001.

D=1.0c/ωpi

Ti/Te=8 (ion carry most current)

Electron E×B drift and generate electron vortices

The ion flow pattern in the current sheet is globally modulated by KHI, nonlinear evolution of KHI can permit LHDI to be unstable at the edge of KH vortexes.

No electric field right at the neutral can be found.

Simulation of LHDI Recent Results

USTC School of Earth and Space Sci.

•与三维磁重联的耦合 包含低混杂漂移不稳定 性的三维全粒子模拟可 在短时间内快速触发磁 重联。

Scholer 2003 Phys. Plasmas

Simulation of LHDI Recent Results

Simulation of LHDI Recent Results

Simulation of LHDI Recent Results