What is Plasma
Low detail definition:
Plasma is the 4th state of matter, beyond solid, liquid and gas.
A plasma is a quasineutral gas containing positively, negatively
and neutrally charged particles. The motions of these particles also depend
on the local conditions and also on the plasma conditions away from
the region concerned.
When an ionized gas is quasineutral, we mean that the number
of electrons is approximately equal to the number of ions (ne ~= ni ~=
n, where n is a common density). That is to say that the plasma is almost
neutral enough to take this limit, but not neutral enough to remove all
the electromagnetic forces.
A plasma is a very hot gas, where some or all of the atoms are separated
into ions & electrons. As the negative and positive charges are free
to move, plasma is an excellent conductor and is influenced by magnetic
and electric fields. Most space plasmas have a very low density, for example
the Solar Wind which averages only 10 particles per cubic-cm. Inter-particle
collisions are unlikely - hence these plasmas are termed collisionless.
Examples of solar system plasmas include:
- The Sun's interior plasma (collisional - fusion ) - Fuel and product of
solar nuclear fusion.
- Solar Wind (collisionless) - A stream of particles from the hot solar corona
which flows throught the solar system at 400 km/s on average.
Cometary Plasma (collisionless at distance from comet) - Outgassing neutral
particles are ionized by solar ultraviolet and collisions with the solar
Planetary Magnetospheric Plasma (collisionless) - See below
- Ionospheric Plasma (collisional) - Exterior layer of the atmosphere.