Plasma - Ms-Kelly

Plasma

What Is It?

•
A hot ionized gas

•
The ‘fourth state of matter’

–
Unlike gases, solids, or liquids, plasma does not
contain molecules

–
Instead, it is a gas that is composed of ions

•
Composes more than 99% of the known visible
universe

So What’s In It?


•
Some, or all, of the electrons in the outer
orbitals have been stripped away


•
The result is a collection of ions and
electrons, which are no longer bound
together


What Did That Mean?


•
Because the particles are not neutral:

–
Plasma behaves differently then regular
gases

–
For instance, in the presence of
electromagnetic fields

Who Found It?


•
First discovered by Sir William Crookes, in
1879


•
But it wasn’t called ‘plasma’ until 1928,
when Irving Langmuir coined the term

Characteristics:
Temperature

•
Defines two kinds of plasma:
Cold

and
Hot

•
Refers to the electron temperature

•
Ion temperature may be very different (lower)




•
Lightning

is an example of plasma present at
Earth's surface. Typically, lightning discharges
30,000 amperes, at up to 100 million volts, and
emits light, radio waves, X
-
rays and even
gamma rays.

Cold Plasma

•
Isn’t really cold

–
Typical electron temperatures for cold plasmas are in
the thousands of degrees

•
Only a small fraction of the gas molecules are
ionized (degree of ionization)

–
Usually on the order of 1%

•
Often created using strong electric fields

Cool

Where Can I Find Cold Plasma?


•
Fluorescent Lights


•
Strobe Lights


•
Experimental Fusion
Research Devices

Hot Plasma

•
Really hot

–
Like the Sun (15,000,000
°

C at the core)

•
The molecules are nearly if not fully
ionized

•
Created by heating the molecules to
extremely high temperatures

Scorching

Where Can I Find Hot Plasma?

•
In Nature, actually

–
The Sun and other stars

–
Lightning

–
The Aurora Borealis

Characteristics:
Potentials

•
Plasmas are excellent conductors

•
Simple view:

–
Due to the above, the electric fields in
plasmas tend to be very small

•
Quasineutrality:

–
On the one hand, we can assume that
densities of positive and negative charges are
equal

–
However, we can assume that electric fields
exist as needed for the physics at hand

An Application:

Let’s Get Hands On (sort of)

•
Plasma Globes

–
An electrode sitting inside a vessel containing
some kind of inert gas

–
The electrode is energized by a high
-
voltage,
high
-
frequency power supply

–
This globe uses voltages around 10 000 volts,
and frequencies ranging from a few kilohertz
to a few 10’s of kilohertz