Reflecting the physics problems and the mix of presumptions of electrostatics with electrodynamics described in the preceding chapter, there may be questions as to what extent the earlier definition of plasma is still valid: Plasma is a physical state of high electrical conductivity and mostly gaseous mechanical properties at high temperature.
This is to be compared with the usual definition that “plasma is the fourth state of matter: solid, liquid, gas, and plasma.” This latter definition conflicts with the fact that the plasma state is possible in solids and liquids (metals and semiconductors). This brings us back to the physics before the middle of the 19th century, especially before Maxwell’s theory. The theory of electricity was then based on electrostatics [Coulomb’s law, electric fields (definition of force E or through the quantity of charge density D) and the connection to magnetic fields H or B given by Ampère’s and Faraday’s laws]. The media were polarizable bodies (solid, liquid, or gas) used in condensers or in electrophoresis. Metals were strange: one needed metals to show the Ampère current that produced the magnetic field H around the conductor, or in Faraday’s closed wire loop within which the temporal change of the enclosed magnetic field B produced a voltage. But what was the dielectric constant of a metal? In electrostatics, one could not define this easily. A metal between two condenser plates discharged the plates, and no polarization appeared from the dielectric insulators.
Online access to SPIE eBooks is limited to subscribing institutions.