2. physics of space plasma
TRANSCRIPT
2.PhysicsofSpacePlasma
LetUniformB,E=0,Binthezdirection
2.2 SINGLE-PARTICLE MOTION
Gyrofrequency,cyclotronfrequency
Gyroradius,cyclotronradius,Larmor radius
ExB driftNocurrent
Externalforce driftCurrent
GradientBdrift
Thefirstadiabaticinvariant
Themirrorpoint
Thethirdadiabaticinvariant
ThesecondadiabaticinvariantThefirstadiabaticinvariant
The total magnetic flux Φ enclosed by a drift surface is the third adiabatic invariant
• Characteristicsofplasma:Quasineutrality,collectivebehavior,goodconductor.
• Phasespace:3Ddisplacement+3Dvelocity• Thephase-spacedensityfunctionf(r,v,t)isalsocalledthesingle-particledistributionfunction.
• Volume=dv dr =dvx dvy dvz dxdy dz• Thedifferentialphase-spacevolume=f(r,v,t)dv dr
2.3 COLLECTIONS OF PARTICLES
Thezerothmomentofthedistribution
Thefirstmomentofthedistribution
Theaveragekineticenergyperparticleofstypeinaunitvolumeoftheplasma
Thehydrostaticpartialpressure
whereN isthenumberofindependentcomponentsofvelocity,Ps isinPascale(Pa),1Pa=1N/m2.
V t
IdealGasLaw:P=nKT
Forthesysteminequilibrium
Maxwellian distribution
V t
ForUs=0
2.4 THE PASMA STATE
DebyeShieldingPlasma Density
ne(m-3)Electron temperatureT(K)
Magnetic fieldB(T)
Debye lengthλD(m)
Gas discharge 1016 104 -- 10−4
Tokamak 1020 108 10 10−4
Ionosphere 1012 103 10−5 10−3
Magnetosphere 107 107 10−8 102
Solar core 1032 107 -- 10−11
Solar wind 106 105 10−9 10
Interstellar medium 105 104 10−10 10
Intergalactic medium
1 106 -- 105
Source:Chapter19:TheParticleKineticsofPlasmahttp://www.pma.caltech.edu/Courses/ph136/yr2002/
Spacecraft (satellite) potential
ND>1=>g<<<1(hightemperature,lowdensity)
characteristictime,characteristiclength,collisionfrequency,meanfreepath,gyrofrequency,gyroradius,plasmafrequency,Debyelength
Fp =9000N1/2,plasmafrequencyFp inHz,electrondensityNin#/cm3
Plasmafrequency
0eexnE e=
Gyro-motion
Gyro-radius
Gyro-frequency
Meanfreepath
http://abyss.uoregon.edu/
l>>rH (ν<<ω),Collisionlessplasmal<<rH (ν>>ω),Collisionplasma
Scaleheight
Height
Density,N
A
B
在溫度相同時,物種A的質量___物種B的質量
在質量相同時,物種A的溫度___物種B的溫度
在電漿中,同時考慮電子與質子兩種不同的物質
經過簡化後可得到標尺高為:
2.4 THE FLUID DESCRIPTION OF A PLASMA
Hydrodynamicsvs.Magnetohydrodynamics (MHD)Individualparticlemotionsvs.Propertiesofacollectionofmanyparticles
Frozen-influx
Frozeninmagneticfield
òò ×= sdB !!fMagneticflux
[ ]òò òòòòòòòòD
×+×´´Ñ=D
×+׶¶
=×=dtsdBsdBu
dtsdBsd
tBsdB
dtd
dtd )()()( !!!!!
!!!!
!!f
[ ] 0)()()()( =´×+×´=D
×+×´´Ñ= òòòò òò lduBldBudtsdBsdBu
dtd !!!!!!
!!!!!f
0=dtdf
Solarwind