Plasma

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Plasma

• A Basic Introduction
• Some Cool Stuff

Matthew WanPHYS 420
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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

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So Whats 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

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What Did That Mean?

• Because the particles are not neutral
• Plasma behaves differently then regular gases
• For instance, in the presence of electromagnetic
  fields

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Who Found It?

• First discovered by Sir William Crookes, in 1879
• But it wasnt called plasma until 1928, when
  Irving Langmuir coined the term

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Characteristics Temperature

• Defines two kinds of plasma Cold and Hot
• Refers to the electron temperature
• Ion temperature may be very different (lower)

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Cold Plasma

• Isnt 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

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CoolWhere Can I Find Cold Plasma?

• Fluorescent Lights
• Strobe Lights
• Experimental Fusion Research Devices

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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

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ScorchingWhere Can I Find Hot Plasma?

• In Nature, actually
• The Sun and other stars
• Lightning
• The Aurora Borealis

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Characteristics Density

• Plasma (electron) density
• The number of free electrons per unit volume
• Ion density
• Related to above by the average charge state

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Density

• Neutral Density
• In hot plasmas, this quantity is very small, but
  may still determine important physics
• The degree of ionization is given by

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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

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An ApplicationLets 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
  10s of kilohertz

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The Power Supply
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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

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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

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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

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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

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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

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BE CAREFUL

• The currents and voltages in this project are
  extremely dangerous
• Touching the wrong part could seriously harm you
• Ive already zapped myself. It hurt.