Plasma Physics (which is synonomous with Plasma
Engineering) is the study of matter in the plasma state. The so-called fourth
state of Matter, a Plasma is basically an ionized Gas in combination with Free Electrons,
where the source of those Electrons are the Atoms/Molecules of that Gas that have had
one or more of their outer Electrons striped away. The resulting soup is a set of
interpenetrating Fluids of Free Electrons and the left-over Ions. Since Electrons
and Ions are electrically charged Particles, they create and are influenced by Electric
and Magnetic Fields. The Equations prescribe the behavior of those Fluids as
they interact with the Electromagnetic Fields. The reason why Space Physicists and
Astrophysicists are interested in Plasmas arises from the observation that more than
99% of all the observable Matter in the Universe exists in the Plasma state (that
includes interplanetary, interstellar, and intergalactic Space, in addition to Stars).
This set of Equations was selected for the background to establish the perspective that
all that we are (as members and participants in the Universe) and can observe
(of that Universe) is by virtue of electromagnetic phenomena. Electromagnetism is
running all the time in the background of the Universe at all temporal and spatial
Scales. The Speed of Light is placed at the vertex of the Triangle and at the bottom
since it is the ultimate speed limit and ties together all things electromagnetic.
Of course, on the truly cosmological scale, Gravity is the final arbiter,
as moderated by Quantum Mechanics.
For those of you who are die-hards, the following is a more detailed but very brief description
of the Equations. Alright, all in one sentence: The equation set consists of the Boltzmann
Equation [top line], which controls the time evolution of the Particle Distribution Functions
fn for each separate Fluid Species n of
electrical particle in six-dimensional Phase Space (Electrons, Ions, and neutral Atoms); four
coupled vector Partial Differential Equations (collectively called Maxwell's Equations)
[second line and the first equations of the third and fourth line] that describe the
relationships between the Electric Fields (E and D) and
the Magnetic Fields (H and B) and their sources, the
Volume Charge Density ρ and the Electrical Volume Current
Density J; two Constituent Equations [second equations of
the third and fourth lines] describing the relationship (1) between the Electric
Field E, the Displacement Field D, and the local
Polarization P of Matter (if any), and (2) between the Magnetic
Field Intensity H, the Magnetic Flux Density B, and
the local Magnetization M of Matter (if any); and one result
[bottom equation], the Speed of Light in vacuum c in terms
of the Permitivity of Free Space εo
and the Permeability of Free Space μo
(This is the natural result mentioned earlier that comes out of Maxwell's
Equations, which indicates that light is an Electromagnetic Wave.*).
Whew! The study of Plasma Physics requires first a year's worth of study of Electromagnetic
Fields and Waves (as a Junior or Senior), and an introduction to the theory of
Fluid Mechanics, which is frequently combined with the introductory courses in
Plasma Physics.
*This natural result marks the first time in the history of Science that a theoretical
prediction came first and the experimental verification came second. As James Clerk
Maxwell constructed what is now known as modern Electromagnetic Theory in the 1860's
from what was experimentally known up to that time about Electric and Magnetic Fields,
there had been no suspicion that Electric and Magnetic Fields had anything to
do with Light. Maxwell intended simply to put all the collective (experimental)
knowledge about such Fields on a solid mathematical basis. (He invented Vector
Calculus and its notation as part of that effort.) One unexpected conclusion
that arose from his mathematical theory was the existence of electric waves
coupled with magnetic waves. These coupled Electromagnetic Waves
are required to propagate at a very specific Velocity, equal to the inverse
of the square root of the product of the Permitivity ε
o and Permeability μ
o of free space. The values of the Permitivity and
Permeability were well known experimentally, but thought to be of significance
only for electric and magnetic Forces. When Maxwell inserted the
numerical values into the propagation velocity Equation (i.e., the bottom
Equation of the triangle of Equations), out popped a value very
close to the known Speed of Light, measured by completely different
techniques than those for the Permitivity and Permeability. Although
Light was well known by then to be a Wave, no one knew of what
Light Waves could be constructed! (Water Waves are Perturbations
of the surface height of a lake, and Sound Waves are Perturbations
of the air pressure, for example, but no one had a clue of what
Light Waves could be a Perturbation.) This strongly implied that
Light is an Electromagnetic Wave. Further, Maxwell's theory
predicted electromagnetic Waves of widely different frequencies, leading
to the discovery Radio Waves, for example. Unfortunately,
Maxwell did not live to learn of experimental verifications of
his predictions, first performed by Heinrich Hertz in 1886.
James Clerk (the e in Clerk is pronounced as a long a, as in the word
care) Maxwell ranks with Isaac Newton and Albert Einstein as one the best,
brightest, and most influential Physicists of the past 450 years. Einstein constructed
his Special Theory of Relativity from Maxwell's Electromagnetic Theory: Special
Relativity is in fact buried in its entirety inside Maxwell's theory.
© 2002 Stevens F. Johnson and Dept. of Physics/Science, Bemidji State University.
All rights are reserved unless explicitly stated otherwise.
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