1. A Basic Introduction & Some Cool Stuff
Plasma
A Basic Introduction
&
Some Cool Stuff
Only a basic explanation; the physics is upper level university.
Who has ever heard of plasma?
Matthew Wan PHYS 420

2. 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
Hot is relative; explained later

3. 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
Atoms have a nucleus, with electrons orbiting at different levels (acknowledge that this is greatly simplified)
These particles are charged

4. What Did That Mean? Because the particles are not neutral:
Plasma behaves differently then regular gases
For instance, in the presence of electromagnetic fields
i.e.: can use magnets to manipulate plasma, such as in a fusion reaction
Magnetohydrodynamics

5. 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
Little bit of history:
Crookes called it ‘radiant matter’

6. Characteristics: Temperature
Defines two kinds of plasma: Cold and Hot
Refers to the electron temperature
Ion temperature may be very different (lower)
Three major characteristics: temperature, density, potentials, in order of importance

8. 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
Relative temperatures, as stated on first slide
Also known as technological plasmas

9. Cool Where Can I Find Cold Plasma?
Fluorescent Lights
Strobe Lights
Experimental Fusion Research Devices
Generally ‘man-made’

10. Hot Plasma Really hot The molecules are nearly if not fully ionized
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
Degree of ionization is close to 100%
Usually natural processes as opposed to man-made

11. Scorching Where Can I Find Hot Plasma?
In Nature, actually
The Sun and other stars
Lightning
The Aurora Borealis
Also in fire

12. Characteristics: Density
Plasma (electron) density
The number of free electrons per unit volume
Ion density
Related to above by the average charge state:
<Z> is the average charge state of the ions

13. Density Neutral Density The degree of ionization is given by:
In hot plasmas, this quantity is very small, but may still determine important physics
The degree of ionization is given by:
Because cold plasmas have a low degree of ionization, there are more neutral particles in the plasma, thus the neutral density is higher

14. 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
So they allow us to make the needed approximations
Navier-Stokes equations and Maxwell’s equations combine to describe electrically conducting fluids. Plasmas fit this description.
These differential equations must be solved simultaneously; in all but the most trivial cases, symbolic (algebraic) solutions are impossible.
Super computers have been used to find numerical solutions

15. 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 volts, and frequencies ranging from a few kilohertz to a few 10’s of kilohertz

16. The Power Supply:

17. How It Works The IC sends out pulses which trigger a transistor
This causes a pulse of voltage to pass through the coil
This induces a large burst of voltage on the secondary of the coil

18. Which Does?
The large voltage produced by the coil can be harnessed to produce a cold plasma
The light bulb contains an inert gas that is relatively easy to ionize
With any gas, a small fraction of the particles are always ionized

19. Cosmic
Cosmic rays that are constantly bombarding the Earth ionize some of the particles
The voltage and current from the power supply accelerate these particles
As they move around the vessel, they ionize other particles

20. Exciting The other particles are excited into a higher energy state
As they come back down to their ground state, they release the extra energy:
Light, in the form of photons
Because particles have unique wavelengths, the colour of the plasma depends on the gas inside the vessel

21. Pressure The gas vessel is at a reduced pressure
As a result, the particles are spaced out
This gives them time to accelerate
If the particles were tightly packed, they would not build up enough energy to initiate a cascade effect

22. BE CAREFUL
The currents and voltages in this project are extremely dangerous
Touching the wrong part could seriously harm you
I’ve already zapped myself. It hurt.