Astrophysical Plasma - Space Plasma Characteristics

Space Plasma Characteristics

Space plasma pioneers Hannes Alfvén and Carl-Gunne Fälthammar divided the plasmas in the solar system into three different categories:

Classification of Magnetic Cosmic Plasmas

Characteristic Space plasma density categories
(Note that density does not refer to only particle density)		 Ideal comparison
High density Medium Density Low Density
Criterion λ << ρ λ << ρ << lc lc << λ lc << λD
Examples Stellar interior
Solar photosphere		 Solar chromosphere/corona
Interstellar/intergalactic space
Ionosphere above 70 km		 Magnetosphere during
magnetic disturbance.
Interplanetary space		 Single charges
in a high vacuum
Diffusion Isotropic Anisotropic Anisotropic and small No diffusion
Conductivity Isotropic Anisotropic Not defined Not defined
Electric field parallel to B
in completely ionized gas		 Small Small Any value Any value
Particle motion in plane
perpendicular to B		 Almost straight path
between collisions		 Circle
between collisions		 Circle Circle
Path of guiding centre
parallel to B		 Straight path
between collisions		 Straight path
between collisions		 Oscillations
(e.g. between mirror points)		 Oscillations
(e.g. between mirror points)
Debye Distance λD λD << lc λD << lc λD << lc λD >> lc
Magnetohydrodynamics
suitability		 Yes Approximately No No

λ=Mean free path. ρ= Larmor radius (gyroradius) of electron. λD=Debye length. lc=Characteristic length

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