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Plasma. A Basic Introduction & Some Cool Stuff. Matthew Wan PHYS 420. 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

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A Basic Introduction


Some Cool Stuff

Matthew WanPHYS 420

what is it
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
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
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
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
Characteristics: Temperature
  • Defines two kinds of plasma: Cold and Hot
  • Refers to the electron temperature
  • Ion temperature may be very different (lower)
cold plasma
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
CoolWhere Can I Find Cold Plasma?
  • Fluorescent Lights
  • Strobe Lights
  • Experimental Fusion Research Devices
hot plasma
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
ScorchingWhere Can I Find Hot Plasma?
  • In Nature, actually
    • The Sun and other stars
    • Lightning
    • The Aurora Borealis
characteristics density
Characteristics: Density
  • Plasma (electron) density
    • The number of free electrons per unit volume
  • Ion density
    • Related to above by the average charge state:
  • Neutral Density
    • In hot plasmas, this quantity is very small, but may still determine important physics
  • The degree of ionization is given by:
characteristics potentials
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
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
how it works
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
which does
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
  • 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
  • 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
  • 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
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.