Re: PLASMA PHYSICS - A SHORT HISTORY

From: Dr. Jai Maharaj (usenet_at_mantra.com)
Date: 08/08/04 

Date: Sun, 08 Aug 2004 07:57:14 GMT

PLASMA PHYSICS - A SHORT HISTORY

Forwarded message

[ Subject: Plasma Physics -- (a short) History
[ From: sky watcher (scalarstatic@yahoo.com)
[ Date: 2003-07-07

http://www-spof.gsfc.nasa.gov/Education/whplasma.html

Plasma Physics -- History

When blood is cleared of its various corpuscles there
remains a clear liquid, named "plasma" by the great Czech
medical scientist, Johannes Purkinje (1787-1869). The use
of the term "plasma" for an ionized gas started in 1927
with Irving Langmuir (1881-1957), an American whose
achievements ranged from the chemistry of surfaces to
cloud seeding for promoting rain, and who in 1932 won the
Nobel prize for chemistry. Langmuir worked for the
General Electric Co., studying electronic devices based
on ionized gases, and the way the electrified fluid
carried high velocity electrons, ions and impurities
reminded him of the way blood plasma carried red and
white corpuscles and germs.

Irving Langmuir

As a result of those studies, carried out on relatively
cool and dense plasmas, scientists nowadays can talk of
"Langmuir waves" and fly "Langmuir probes" aboard
satellites. Gradually plasma research spread in other
directions, of which three were particularly significant.

First, the development of radio led to the discovery of
the ionosphere, the natural "plasma roof" above the
atmosphere, which bounces back radio waves and sometimes
absorbs them. Starting with the study of the propagation
of radio waves in the ionosphere, a wide variety of
plasma waves was identified, in general spreading
differently along magnetic field lines than perpendicular
to them.

Second, astrophysicists recognized that much of the
universe consisted of plasmas, and that understanding
astrophysical processes required a better grasp on plasma
physics. This was particularly true for the Sun, whose
intensely magnetic sunspots produced many intricate
plasma phenomena (e.g. solar flares).

Finally, the creation of the atomic bomb raised great
interest in nuclear energy as a possible source of power
for the future. The Sun releases its energy by combining
hydrogen nuclei to form helium, but this thermonuclear
fusion process needs enormous temperatures and pressures,
like those found at the center of the Sun. The process is
easier in a gas consisting of the heavy forms (isotopes)
of hydrogen, but even there, such enormous temperatures
are needed that no laboratory container could hold the
gas--either the container would vaporize, or (more
likely) it would cool the gas to where all nuclear fusion
stopped.

However, since gas at such a temperature becomes a
plasma, the idea arose to hold it trapped inside a
magnetic field, without it actually touching any material
walls. The effort to produce such "controlled
thermonuclear fusion" started with "Project Sherwood" of
the early 1950s and has grown into a great international
undertaking, with thousands of scientists and huge,
sophisticated machines. Gradually ways were found to foil
the different modes by which the magnetic field rapidly
spilled its plasma, and both the temperature and density
of the plasma were slowly increased. Recently a fusion
experiment managed to extract as much fusion energy as
was invested in the plasma, but we are still a long way
from commercial use of such energy.

When satellites discovered the radiation belt and began
exploring the magnetosphere, a fourth direction opened,
space plasma physics. From fusion research, space
scientists borrowed the theory of plasma trapping by a
magnetic field, and from ionospheric physics, the theory
of plasma waves. Astrophysics provided, among other
things, notions of magnetic processes for energy release
and particle acceleration. Today space plasma physics is
an active field, contributing to the understanding of not
just observations in space but also of plasmas in
general.

Further reading:Irving Langmuir's coining of "plasma" was
described by Harold M. Mott-Smith in a letter to Nature,
vol. 233, p. 219, 17 September 1971.

The founding of "Project Sherwood" is described on p.
217-220 of the autobiography of John Archibald Wheeler,
"Geons, Black Holes and Quantum Foam" (Norton and Co.,
1998). The book itself tells a fascinating and inspiring
story, the life of a scientist who was involved in many
frontier areas of physics.

End of forwarded message from "sky watcher" <scalarstatic@yahoo.com>

Jai Maharaj
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