Newsgroups: sci.physics.fusion
Subject: Early Plasmoid Article
From: jim@netlink.cts.com (Jim Bowery)
Date: Mon, 05 Oct 92 09:52:39 PDT
Organization: NetLink Online Communications, San Diego CA

Audit:  sci.physics.fusion,JBowery,2
 
Here's another Scientific American article from the 60's.  Someone
got to the article before I did and put circles around certain key
sections.  I've delimited those sections with < text >:
 
PLASMOIDS
 
These little pieces of plasma(a gas of electrons and ions)
are created in the laboratory with an electrical gun.  They
have an unexpected capacity for maintaining their identity.
 
by Winston H. Bostick
 
In physics laboratories of several countries -- notably the US, 
Great Britain and the USSR -- man is feeling his way gingerly toward
harnessing thermonuclear power.  The studies are centered on small
"bottles" of hot gas which correspond to tiny samples of the sun
(though they are not nearly so hot or dense).  The gas is called a
plasma.  It is a collection of electrons and ions (electrically
charged atoms).  The behavior of this assemblage of particles is at
once very simple and very complex.  It challenges all the mathematical
and experimental ingenuity of modern physics, and it has ushered us
into a world of unexpected and exciting phenomena.  This article is an
account of some recent experiments which have generated remarkable
bodies that we call plasmoids.
 
The properties of these bodies stem basically from two familiar
phenomena of nature, both of which, oddly enough, go back to the same
discoverer -- William Gilbert, Queen Elizabeth's physician, who will
forever be a great name in physics.  In 1600 this imaginative
experimenter placed an electrically charged knob of metal close to a
flame and found that the metal lost its charge:  the heated air had
carried it away.  Thus Gilbert discovered that a gas (an ionized gas,
as we know now) can conduct electricity.  The other physical
phenomenon that governs the behavior of plasmoids is magnetism -- a
field in which Gilbert was also the first experimenter.  Ionization
and magnetism combine to produce what have recently become known as
magnetohydrodynamic effects, and plasmoids are magnetohydrodynamic
phenomenon [see "Electricity in Space," by Hannes Alfven: Sci Am May,
1952].
 
The late Irving Langmuir of the General Electric Company began to
study plasmas as long ago as 1921.  Plasmas, of course, are nothing
new:  whenever we look at a neon sign we see a plasma.  It is produced
by an electric discharge which knocks electrons fro the gas atoms in
the tube; the released electrons collide with other atoms and produce
more ions.  This process continues until there are enough liberated
electrons to make the gas a good electrical conductor.
 
Langmuir was interested in learning, among other things, the energy of
agitation, or "temperature," of the electrons.  The wall of the neon
tube is cool, and so are the ions and gas atoms in the tube, because
comparitively few atoms are ionized and the ions quickly distribute
their energy among the neutral atoms.  But the electrons are so much
lighter that they lose little energy in rebounding from the more
massive atoms or the tube wall.  By ingenious experiments Langmuir
measured the electrons' temperature and found that it amounted to
about 20,000 degrees Fahrenheit -- about twice as hot as the sun's
surface.
 
This high figure explains the interest in plasmas on the part of
physicists who are now studying the possibilities for achieving
controlled thermonuclear fusion.  To fuse atoms of deuterium 
(heavyhydrogen) on a large scale requires temperatures of about 300 
million
degrees centigrade.  Such a temperature is far beyond our reach in the
laboratory, nor could a dense gas at this temperature be contained by
any method we know at present.  But for exploratory experiments it
should at least be possible to reaise a plasma to a temperature of
scores ofthousands of degrees, and the plasma can be contained if its
density is sufficiently low.
 
The difficulty is that ina low-density gas, energized ions and
electrons do not collide with one another often enough to raise the
temperature greatly; instead they lose their energy in collisions with
the walls of the container.  But as everyone who has followed events
knows, a beautiful solution to this problem has been found.  It is the
magnetic "bottle."  Within a magnetic field, which swings the
electrified particles in circular orbits, the plasma can temporarily
be held in thrall as tightly as by any material container.  The
electrons and atoms collide only with one another, and the plasma
becomes fully ionized.
 
In the University of California Radiation Laboratory at Livermore and
at the Stevens Institute of Technology we have been studying
magnetically confined plasmas with the help of a special plasma gun. 
It generates a plasma of deuterium, the potential fuel of
thermonuclear fusion.  There are two electrodes, made of titanium with
deuterium atoms absorbed in them.  A pulsed arc current of several
thousand amperes, each pulse lasting about half a microsecond, is
passed across the gap between the electrodes.  This high current
evaporates electrons and ions from the two electrodes.  It also
generates a magnetic field which, like a girdle, pinches the plasma
into a slender column.  The special feature of our gun is that the
plasma emerging from the two "mouths" is bent ito a loop, and it fires
doughnut-shapped blobs of plasma.  Just as, when a spring is bent, the
turns of the wire are crowded closer on the inside of the loop than on
the outside, so the magnetic field lines of the loop of plasma
emerging from our gun are more crowded on the inside than on the
outside.  The strong magnetic pressure on the inside of the loop blows
the plasma forward at high speed -- up to 120 miles per second! 
Considering that the gun smaller than a thimble and that the driving
energy stored in the capacitor is only six joules -- no more than is
needed to light a six-watt bulb for one second -- this is a truly
remarkable performance.  A velocity of 120 miles per second for
deuterium ions represents a temperature of four million degrees.  <It
suggests that with larger plasma guns of this kind we might begin to
approach thermonuclear termperatures.
 
The velocities of the plasma bodies shot from our gun are comparable
to the speed of stars in galaxies and of flares shooting out from the
sun.  It seemed worthwhile to follow up the analogy.  Would the 
highspeed plasma serve as a kind of laboratory model to throw light on 
the
magnetohydrodynamic processes operating in the universe?  We have
studied it from this point of view, with what seem to me interesting
and significant results.>
 
Let us see first what happens when we fire a piece of plasma into a
vacuum under an external magnetic field (that is a field applied from
outside the plasma itself, which is bottled within its own selfexcited 
field).  Although the plasma darts through our chamber at a
speed in the neighborhood of 120 miles a second, fortunately it leaves
a luminous wake which can be photographed with a high speed camera, so
that we can see its track.  Now we would expect the electrons and ions
in the plasma to be thrown into circular orbits as soon as they enter
the externally applied magnetic field, so that the plasma would not
move more than a very short distance from the gun.  But the camera
discloses the somewhat shocking fact that thte plasma crosses the
magnetic field with ease!  How does it get through the field?
 
To follow our explanation the reader is advised to consult the
accompanying diagrams. [jb: sorry folks -- go get the original].  As
the plasma starts to move across the magnetic field, the electrons
move upward and the positive ions downward.  This effect essentially
produces an electromotive force, <just as copper wirs moving across a
magnetic field do in anordinary dynamo.  An electromotive force can be
thought of as the electric pressure exerted by an electric pump.  If
there is no outlet (such as an electric toaster) for the pump, no
curent will flow.  Similarly this little piece of plasma has no outlet
in the vacuum chamber and no current can flow.  Its pump pushes aainst
closed valves, so to speak, and merely creates an electrical pressure
opposing that of the pump.  Within the plasma frame of reference the
direct and opposing electric fields cancel each other, and the
magnetic field swings the electrons and ions in perfectly circular
orbits.  But from our outside point of view we can see that the
opposing electric field (E2), in conjunction with the magnetic field,
moves the orbits, so that the plasma travels across the magnetic
field.  The particle orbits trace a track such as a marker at one
point on the edge of a merry-go-round would leave the ground if the
merry-go-round were dragged along by a tractor while it was turning.
 
Apparently some ions and electrons in the plasma, escaping the full
effect of electric field E2, stay behind in stationary circular
orbits.  These ions and electrons recombine and give off light.  Their
luminous tracks are in a manner of speaking, the funeral pyres of the
particles which were sacrificed in laying down the electric field E2
so that the main body of the plasma might pass across the magnetic
field.
 
We can actually draw current from the primary electric field produced
by the little dynamo contained in this plasma.  If we put two small
stationary probes connected by a resistance in the chamber (equivalent
to plugging in a toaster), we get a pulse of current of about one
ampere as the two regions of the plasma pass simultaneously over the
probes.
 
Further measurements with probes show that the plasma forms an ever
elongating hollow cylinder as it proceeds across the magnetic field
[see upper diagram at left].  It is to this type of plasma -- a 
selfgenerating, shaped body -- that we have given the name plasmoid.  
And
plasmoids, under laboratory manipulation, display some fascinating
behavior.
 
 
What will happen if we fire two plasmoids at each other from opposite
directions?  We might suppose that when they meet their transverse
electric fields will cancel each other so that both plasmoids stop
dead.  But in fact they bounce off each other like billiard balls! 
Apparently each dynamo acts as an outlet or short-circuit for the
other, and a substantial current (several amperes) flows briefly.  The
current gives rise to a "cushion" of high magnetic-field pressure
between the two plasmoids which pushes them away from each other.
 
Occasionally two plasmoids crashing head on break into fragments, but
even these fragments seem to behave as entities.  In other words, we
appear to be dealing with bodies which have strong powers of 
selforganization and preservation.  We find these powers still more
strikingly demonstrated when we go on to further experiments.  
 
Suppose we fire a plasmoid not into a vacuum but into a thin gas.  We
introduce into the chamber a little deuterium gas, amounting to a
pressure of about one micron.  Now when a plasmoid is fired into the
chamber through a magnetic field, the gas, which becomes somewhat
ionized by the firing, allows current to flow.  The current slows the
movement of the plasmoid and also twists its path and its shape.  When
we fire four (or eight) plasmoids at one another from different
directions, upon meeting near the center they whirl and form a ring
with spiral arms [see photogrph above].  The formation looks
strinkingly like a photograph of a spiral galaxy.  If we fire two
plasmoids at each other head on, they form an S-shaped figure
resembling a "barrel" spiral galaxy [see photograph below].
 
Just how are these interesting shapes formed?  We can explain them on
the basis of complicated interactions between the plasmoids and the
magnetic field, which are diagrammed here for readers versed in
electricity and magnetism who may be interested in the mechanism [see
diagrams on page 91].
 
A barrel spiral, it appears, may be formed by plasmoids joining head
to head; a ring spiral, by plasmoids joining head to tail.  When the
ring is oval shapped, part of it flips over and forms a figure eight.
 
Photographs of plasmoids in three diensions show that as a plasmoid
moves across the magnetic field it is twisted into the shape of a
left-handed screw [see diagram at top of page 91].  It is amusing to
speculate on the possible relation of this fact to the recent
breakdown of the parity principle, when it was found by particle
experiments that the matter of our universe has a preferred lefthanded 
spin [see "The Overthrow of Parity", by Philip Morrison;
Scientific American, April].  If we reversed the poles of the magnetic
field and the sign of the curren tin our plasma gun, our plasmoids
would be right-handed instead of left-handed.  The tempting
speculation is that the matter of our galaxies may have been formed
under the influence of vast galactic magnetic fields of one
predominant orientation, which gave our matter a left-handed bias.
 
 
Under certain conditions our plasmoids form a pair of rings, which do
not stay in the center of the chamber but move away from each other in
opposite directions [see diagrams at left].  We believe that these
rings are basically similar to magnetohydrodynamic whirls which,
according to Alfven, are apparently formed in pairs in the interior of
the sun and may be responsible for sunspots.  However, our plasma
rings are not whirls in a flud but are sparate, independent "bodies." 
As such they represent a form of ordred organization by nature of
which we have not been fully aware until now.  Here is a case of
electrons and ions collaborating with a magnetic field to form bodies
which, though inanimate, assume orderly, characteristic shapes and
possess a firm integrity.
 
<We can look upon the combination of plasma and magnetic field as a
kind of self-shaping putty.  Perhaps study of the forms assumed by
this putty may help us to u nderstand configurations such as the stars
and galaxies.  It may also through light, at the other end of the
scale, on the construction of fundamental particles such as the
electron, the proton, mesons and neutrinos.  They too may be made of a
self-organizating putty:  a putty composed of the electromagnetic
field and its own gravitational forces, which, working togeher, create
the bodies we know as particles.>