1 / 22

Plasma

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

royce
Télécharger la présentation

Plasma

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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.

More Related