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  1. Plasma A Basic Introduction & Some Cool Stuff Matthew WanPHYS 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

  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

  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

  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

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

  7. 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

  8. CoolWhere Can I Find Cold Plasma? • Fluorescent Lights • Strobe Lights • Experimental Fusion Research Devices

  9. 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

  10. ScorchingWhere Can I Find Hot Plasma? • In Nature, actually • The Sun and other stars • Lightning • The Aurora Borealis

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

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

  13. 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

  14. 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

  15. The Power Supply:

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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.