ELECTRON NUMBER DENSITY IN A SLIGHTLY IONIZED-GAS (ARGON INDUCTIVELY-COUPLED PLASMA)

An equation defining the electron number density, n(e), in an argon in ductively coupled plasma (ICP) regarded as a slightly ionized gas, is derived in terms of the thermodynamic temperature and the electronic c hemical potential of the parent species in the ionization. The ICP is not regarded as being in a state of local thermodynamic equilibrium, b ut instead is considered to be an example of a thermodynamic steady st ate. The derivation requires nothing more advanced than elementary sta tistical thermodynamics, and the result is compared in detail with the Saha relation. It is shown that the new equation requires thermodynam ic temperatures much lower than those from the Saha relation, and othe r areas of atomic emission spectroscopy to which the basic formulation is applicable are indicated.