Plasmas are a quasineutral gas of charged and neutral particles which exhibit collective behavior (F. Chen, Introduction to Plasma Physics, Plenum Press, 1974, 1984). Typically they consist of negatively charged electrons and positively charged ions, but may include negatively charged ions, negatively charged dust, positrons, etc. Plasmas encompass distinguishable scales ranging from the atomic to the galactic. Topical areas of plasma science are as rich and diverse as for any other state of matter although most applications have emerged only within the past two decades. For an excellent summary of plasma science and technology, see the U.S. National Academy of Sciences Plasma Science Report.
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