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2 -
Plasma -
The Fundamental State of Matter
Definitions
When one or more of the outer (valence) electrons are stripped away
from an atom we say the atom has become 'ionized'. It then exhibits
a net positive electrical charge, and is called a 'positive ion'. On
the other hand, if an extra electron is added onto a neutral atom,
the combination then carries a net negative charge and is referred
to as a 'negative ion'.
The electrical forces between dissimilar
ions are orders of magnitude stronger than any mechanical force such
as that produced by gravity. An electrical plasma is a cloud of ions
and electrons that, under the excitation of applied electrical and
magnetic fields, can sometimes light up and behave in some unusual
ways.
The most familiar examples of electrical plasmas are the neon
sign, lightning, and the electric arc welding machine. The
ionosphere of Earth is an example of a plasma that does not emit
visible light. Plasma permeates the space that contains our solar
system. The cloud of particles that constitutes the solar 'wind' is
a plasma. Our entire Milky Way galaxy consists mainly of plasma.
In
fact 99% of the entire universe is plasma!
History
During the late 1800's in Norway, physicist Kristian Birkeland
explained that the reason we could see the auroras was that they
were plasmas. Birkeland also discovered the twisted corkscrew shaped
paths taken by electric currents when they exist in plasmas.
Sometimes those twisted shapes are visible and sometimes not - it
depends on the strength of the current density being carried by the
plasma.
Today these streams of ions and electrons are called
Birkeland Currents. The mysterious
sprites, elves, and blue jets
associated with electrical storms on Earth are examples of Birkeland
currents in the plasma of our upper atmosphere.
In the early 20th century, Nobel laureat Irving Langmuir studied
electric plasmas in his laboratory at General Electric; he further
developed the body of knowledge Birkeland had initiated.
In fact it
was he who first used the name 'plasma' to describe the almost
lifelike, self-organizing behavior of these ionized gas clouds in
the presence of electrical currents and magnetic fields.
Basic Properties -
Modes of Operation
There are three distinctly different steady state modes in which a
plasma can operate:
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Dark Current Mode - The strength of the electrical current (flow of
charged particles) within the plasma is very low. The plasma does
not glow. It is essentially invisible. We would not know a plasma
was there at all unless we measured its electrical activity with
sensitive instruments. The present day magnetospheres of the planets
are examples of plasmas operating in the dark current mode.
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Normal Glow Mode - The strength of the electrical current (flow of
charged particles) is significant. The entire plasma glows. The
brightness of the glow depends on the intensity of the current in
the plasma. Examples: Any neon sign. Emission nebulae. The Sun's
corona.
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Arc Mode - The strength of the electrical current in the plasma is
very high. The plasma radiates brilliantly over a wide spectrum.
Current tends to form twisting filaments. Examples of this mode of
operation are: An electric arc welding machine. Lightning. The Sun's
photosphere.
In all three modes of operation, plasmas emit measurable
electromagnetic radiation (radio frequency noise). At any given
time, the current density (Amps per square meter) existing in the
plasma, determines which particular mode a plasma is operating in.
The atomic structure of the gas that became ionized to form the
plasma in the first place also is a factor in this.
Double Layers
One of the most important properties of any electrical plasma is its
ability to "self-organize" - that is, to electrically isolate one
section of itself from another.
The isolating wall is called a
double layer (DL). When a plasma is studied in the lab, it is
usually contained in a closed cylindrical glass tube. Electrodes are
inserted into the ends of the tube - one electrode (called the
anode) is maintained at a higher voltage than the electrode at the
other end (the cathode).
If such a voltage difference is applied,
then ionization will be initiated and current will start to flow
through the plasma. Positive ions (atoms with one or more electrons
stripped off) will migrate away from the anode, and negative ions
(atoms carrying one or more extra electrons) will move toward the
anode. The mathematical sum of these two oppositely directed flows
constitutes the total current in the plasma.
If the voltage difference from one electrode to the other becomes
large enough, a DL will form in a narrow cross-section somewhere in
the middle of the tube. Almost all the voltage drop that is applied
across the electrodes will fall across this DL. The plasma on one
side of the DL (the side toward the anode) will have approximately
the same voltage as the anode.
The plasma on the cathode side of the
DL will have essentially the same voltage as the cathode. The two
halves of the plasma are then electrically isolated from one another
by the DL. No electrostatic force is felt by particles on one side
of the DL due to charges on the other side of the DL. The total
electric current, however, is the same throughout the plasma (on
both sides of the DL).
Plasmas are excellent conductors and,
therefore, there will not be a significant voltage drop across them
while they are carrying current - thus the need for the presence of
the DL that 'takes' most of any externally applied voltage. In other
words, the DL is where the strongest electric fields in the plasma
will be found.
If a foreign object is inserted into a plasma, a DL will form around
it, shielding it from the main plasma. This effect makes it
difficult to insert voltage sensing probes into a plasma in order to
measure the electric potential at a specific location. This is a
well known property of plasmas. Various methods have been developed
in the laboratory to overcome it.
In space, it is impossible to send a spacecraft to measure the
voltage of the solar plasma at some point. Voltage is a relative
measure (like velocity, for example); it must be measured with
respect to some datum. A spacecraft will start out having the same
voltage as the surface of Earth. As it penetrates the plasmasphere
and enters the solar plasma it will slowly accumulate charge and
thus alter its voltage.
The strength of an electric field, however,
can be measured in space.
The Z-Pinch
Electric current, passing through a plasma, will take on the
corkscrew (spiral) shape discovered by Birkeland. These Birkeland
currents most often occur in pairs. There is a tendency for these
pairs to compress between them any material (ionized or not) in the
plasma. This is called the "z-pinch" effect.
The ability of Birkeland currents to accrete and compress even non-ionized material
is called "Marklund convection".
Hannes Alfven and the 'Frozen-in Magnetic Fields'
For years it was assumed that plasmas were perfect conductors and,
as such, a magnetic field in any plasma would have to be 'frozen'
inside it.
The technical explanation is as follows: One of Maxwell's equations
is that the curl of E is equal to -dB/dt. Consequently, if the
electric field, E, in a region is everywhere zero valued, then any
magnetic field in that region must be time invariant (have a
constant value).
So if all plasmas are ideal conductors (and so
cannot have electric fields - that is to say, voltage differences -
inside them), then any magnetic fields inside a plasma must be
frozen - i.e., cannot move or change in any way.
Now we know that there can be slight voltage differences between
different points in plasmas. Plasma engineer Hannes Alfvén pointed
out this fact in his acceptance speech while receiving the Nobel
Prize for physics in 1970. The electrical conductivity of any
material, including plasma, is determined by two factors: the
density of the population of available charge carriers (the ions) in
the material, and the mobility of these carriers.
In any plasma, the
mobility of the ions is extremely high. Electrons and ions can move
around very freely in space. But the concentration (number per unit
volume) of ions available to carry charge may not be at all high if
the plasma is a very low pressure (diffuse) one. So, although
plasmas are excellent conductors, they are not perfect conductors.
Weak electric fields can exist inside plasmas.
Therefore, magnetic
fields are not frozen inside them.
Currents in Cosmic Sized Plasmas
Because plasmas are good (but not perfect) conductors, they are
equivalent to wires in their ability to carry electrical current. It
is well known that if any conductor cuts through a magnetic field, a
current will be caused to flow in that conductor. This is how
electric generators and alternators work. Therefore, if there is any
relative motion between a cosmic plasma, say in the arm of a galaxy,
and a magnetic field in that same location, Birkeland currents will
flow in the plasma. These currents will, in turn, produce their own
magnetic fields.
Plasma phenomena are scalable. That is to say, their electrical and
physical properties remain the same, independent of the size of the
plasma. Of course dynamic phenomena take much less time to occur in
a small laboratory plasma than they do in a plasma the size, say, of
a galaxy. But the phenomena are identical in that they obey the same
laws of physics. So we can make accurate models of cosmic sized
plasmas in the lab - and generate effects exactly like those seen in
space.
In fact, electric currents, flowing in plasmas, have been
shown to produce most of the observed astronomical phenomena that
are inexplicable if we assume that the only forces at work in the
cosmos are magnetism and gravity.
Why Do Astrophysicists Ignore Electrical Phenomena?
When such a firm foundation has been laid for continued work in the
electrical properties of the universe,
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Why do "mainstream"
astrophysicists continue to ignore this field of study and, instead,
patch up their failing "gravity only" models with more and more
arcane, invented theoretical fictions?
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Why do conventional
astronomers and cosmologists systematically exclude electric fields
and currents from not only their consideration, but from their
curricula?
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Why do they intentionally ignore the fact that many
here-to-fore "unexplained" phenomena are quite simply explained by
recognizing the existence of electric fields and currents in solar
and galactic plasma?
The answer is this:
Magnetism was known to exist in the middle ages. They knew, even
back then, that a piece of iron could act on another - at a
distance.
But, the early astronomers (like their modern brethern) were simply
unaware of electrical phenomena. Johannes Kepler (1571-1630) had
already mathematically explained the shape of the orbits of the
planets when Isaac Newton published his treatise on gravity in 1687.
Once that occurred, nothing more was needed to explain and predict
the planetary motions that could be observed in those days.
Everything was solved.
This, of course, was all long before Benjamin Franklin (1706-1790)
flew his kite in a thunder storm or James Clerk Maxwell (1831-1879)
developed his equations relating magnetic and electric fields. But,
electric fields were difficult to measure. And astronomers didn't
know they needed to know about them. So, they never got included in
the "accepted" model of how the solar system or the cosmos works.
That is why, to this day, most astrophysicists have never taken
courses in electromagnetic field theory or experimental plasma
discharges. They attempt to describe the actions of plasma by means
of equations that are applicable only to fluids like water - and
magnetic effects. This is what Alfven called
'magneto-hydrodynamics'. They do not realize, as he did, that the
prefix 'magneto' implies 'electro'.
And that, in turn, explains why
astrophysicists blithely talk about stellar winds, vortex trails,
and bow shocks instead of electrical currents in plasmas, electrical
fields, z-pinches, and double layers.
It also explains why they make
wrong claims about how magnetic fields must pile-up, merge, and
recombine - they are simply uneducated in, and therefore
understandably mystified by, this now well known area of engineering
science.
Recent Development!
The American Institute of Physics has just recently announced that
they will now officially recognize the Plasma Universe as an
official field of study in physics! Eighty years late!
But better
late than never.
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