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University of Nevada, Reno Collisionless Plasma Flow in External Magnetic Field

Collisionless Plasma Flow in External Magnetic Field

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Collisionless Plasma Flow in External Magnetic Field. University of Nevada, Reno. 1D-PIC SIMULATION PARAMETER. Plasma fully ionized hydrogen plasma length : 4 mm collision frequency : ν ce = 2x 10 8 1/sec flow velocity u sw =4x10 7 cm/s External Magnetic Field profile : - PowerPoint PPT Presentation

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Page 1: Collisionless Plasma Flow in External Magnetic Field

University of Nevada, Reno

Collisionless Plasma Flow in External Magnetic Field

Page 2: Collisionless Plasma Flow in External Magnetic Field

Plasmafully ionized hydrogenplasma length : 4 mmcollision frequency : νce = 2x 108 1/sec

flow velocity usw=4x107 cm/s

External Magnetic Fieldprofile : electron gyrofrequency : ωce = 1.76 x 1011 rad/sec @ B =

10 kGelectron gyroradius : re = 16 μm @ B = 10 kG

ion gyroradius : ri = usw/ωci = 0.42cm @ B = 10 kG

Bex0 /(1cm x);7kG@x 0 65kG@x 1cm

Bex0 /(1cm x);7kG@x 0 65kG@x 1cm

Computational Parametermesh size : Δx = 1.426 μmtime step : Δt = 4.65 fstotal simulation time : 20 ns

1D-PIC SIMULATION PARAMETER

x D re ri

x D re ri

t 1/ pe 1/ ce 1/ ci ~1ns < 20ns

t 1/ pe 1/ ce 1/ ci ~1ns < 20ns

Page 3: Collisionless Plasma Flow in External Magnetic Field

TIME EVOLUTION OF ION DENSITY

Page 4: Collisionless Plasma Flow in External Magnetic Field

MAGNETIC FIELD IS PARTIALLY NEUTRALIZED BY SELF-INDUCED FIELD

Negative B-field is excited by electrons circular motion at the plasma expansion front.

Page 5: Collisionless Plasma Flow in External Magnetic Field

NEGATIVE ELECTROSTATIC FIELD IS EXCITED AT PLASMA FRONT

Ion Expansion Front

Since electrons are magnetized, ions go ahead and make a negative sheath field at the plasma

front.

Page 6: Collisionless Plasma Flow in External Magnetic Field

Figure : Electron phase plot X-px (left) & X-py (right) at t=9.3ns

ELECTRONS ARE ACCELERATED BY NEGATIVE SHEATH FIELD AND DO CIRCULAR MOTION

Page 7: Collisionless Plasma Flow in External Magnetic Field

Figure : Ion phase plot X-Px at 4.6 ns (left) and 9.3 ns (right).

IONS ARE DECELERATED BY NEGATIVE SHEATH FIELD

Page 8: Collisionless Plasma Flow in External Magnetic Field

Figure : Energy spectrum at t=9.3ns.

Te~1.2keV (Initial Te ~ 400eV)

ENERGY SPECTRA SHOW IONS LOSE ENERGY AND ELECTRONS ARE HEATED

~ Flow velocity

Low energy ions increases.

Page 9: Collisionless Plasma Flow in External Magnetic Field

Ex u ec

Bnet

Ex u ec

Bnet

i ~ eExs

i ~ eExs

Ions are stopped when they transfer half of their own energy to the electrons

i eu ec

Bnet re

eu ec

Bnet p ec

eBnet

u e p e ~ 2e

i eu ec

Bnet re

eu ec

Bnet p ec

eBnet

u e p e ~ 2e

SUMMARY OF WHAT’S GOING ON

(Assumed the effective collision frequency is the electron cyclotron frequency )

(Assumed the ion energy equals to the sheath potential )

Y. Sentoku, K. Mima, P. Kaw, and K. Nishikawa, Phys. Rev. Lett. 90 (2003) 155001

Page 10: Collisionless Plasma Flow in External Magnetic Field

IONS START FLOWING BACKWARD AFTER 10 NSEC

Page 11: Collisionless Plasma Flow in External Magnetic Field

ne=2x1016 ccm

Te=5keV

usw=8x108 (0.0267c)

Plasma = 1.8mm x 0.72mm

External B-field (Z-direction)100kG@x=0 - 500kG@x=5.4mmωce=1.8x1012 rad/sec @B=100kG

re=20μm@B=100kG

Δx=3.6μmLx=7.1mm, Ly=1.8mm

2D-PIC PARAMETERS

Density is normalized by n0=2x1016 ccm

200kG

Page 12: Collisionless Plasma Flow in External Magnetic Field

t=120 ps

t=360 ps

t=240 ps

TIME EVOLUTION OF ION DENSITY

Page 13: Collisionless Plasma Flow in External Magnetic Field

TIME EVOLUTION OF ELECTRON DENSITY

t=120 ps

t=360 ps

t=240 ps

Page 14: Collisionless Plasma Flow in External Magnetic Field

Ex @ t=60ps

Ey @ t=60ps

Bz @ t=60ps

FIELD STRUCTURE AT T=60ps

Bz = 0.0002~20kG

Ex = 0.0002~5.8 V/m

Page 15: Collisionless Plasma Flow in External Magnetic Field

FIELD STRUCTURE AT T=175ps

Ex @ t=175ps

Ey @ t=175ps

Bz @ t=175ps