Plasma is the 4th state of matter. It is composed of mostly ionized particles and is often viewed as a gas, however exhibits various properties different to that of a typical gas. Although plasma isn't often seen on Earth (aside from lightning, fluorescent tubes, and the Aurora Borealis), some sources say that as much as 99% of the ordinary matter in the universe is plasma.[1] This estimate is based on the idea that all of the stars, gaseous nebulae and interstellar hydrogen are plasmas.

One reason plasma is not so common on Earth is due to the high temperatures required to keep a gas in the plasma state. At average temperatures on Earth there just isn't enough energy for atoms to remain ionized. However, at thousands to millions of degrees Kelvin these energies are available, and plasmas dominate.[1] The nearest example of plasma abundance is in the Sun, where extremely high temperatures rip the electrons from hydrogen and helium atoms.[6]


Since the particles of plasma have charge, it interacts strangely within itself. As the charges move around they can generate local concentrations of positive or negative charge giving rise to electric fields. As well, since the charged particles are moving, they generate currents which gives rise to magnetic fields within the plasma.[1] These fields affect the motion of other charged particles far away, so this system is extremely dynamic.

Because of this behaviour, plasma does not tend to conform to external influences, rather it behaves as if it had a mind of its own.[1] For a gas to be considered a plasma it must be dominated by electromagnetic forces rather than collisions with neutral atoms. Therefore plasmas are often considered to be highly ionized, rather than allowing for weakly ionized gases to fit into the category.

Applications of plasma physics

Plasmas are very useful due to them covering a wide range of configurations; their particle density ranges over 28 orders of magnitude from [math]10^6[/math] to [math]10^{34}[/math] particles per cubic meter, and their energy ranges over 7 orders of magnitude.[1] Some applications include:

  • Gas discharges - these are encountered in mercury rectifiers, ignitrons, spark gaps (ie. spark plugs), neon and fluorescent lights, and lightning.
  • Controlled fusion - the beginnings for controlled nuclear fusion occurred in the mid 1950's after hydrogen bomb's fusion abilities were already known. The basic reactions involve the use of deuterium and tritium atoms colliding at high enough energies in order to fuse together. Plasmas are necessary for this in order to maintain high enough energies, however the problem of heating and containing a plasma efficiently is still largely unresolved.[1]
  • Space and astrophysics - the study of the solar wind that constantly bombards the Earth, responsible for the phenomena of Aurora Borealis, concerns plasma because this wind is highly ionized particles interacting with the Earth's magnetic field. The study of stellar dynamics also concerns plasma.

For Further Reading

For further information please see the related pages below:


  1. 1.0 1.1 1.2 1.3 1.4 1.5 F. Chen, "Introduction," in Introduction to Plasma Physics and Controlled Fusion, 2nd ed., New York: Springer, 2006, ch.1
  2. Wikimedia Commons [Online], Available:
  3. Wikimedia Commons [Online], Available:
  4. Wikimedia Commons [Online], Available:
  5. Wikimedia Commons [Online], Available:
  6. Jefferson Labs. (Accessed October 18, 2015). What is plasma? [Online], Available: