Validity conditions for complete and partial local thermodynamic equilibrium of nonhydrogenic level systems and their application to copper vapor arcs in vacuum

Validity conditions for complete and partial local thermodynamic equilibrium (CLTE and PLTE) of homogeneous, time-dependent, and optically thin plasmas are derived. For Cu I, electron densities of n/sub e/>or=(5*10/sup 22/-5*10/sup 23/) m/sup -3/ are required for the establishment of CLTE. For Cu I and Cu II, n/sub e/>or=(5*10/sup 21/-5*10/sup 21/-5*10/sup 22/) m/sup -3/ is necessary for PLTE (for electron temperatures of 1-2 eV). Application to low-current copper vapor arcs in vacuum shows that CLTE can be expected for r<200-600 mu m (r=distance from the cathode spot). A further limitation follows for temperatures of 2 eV or higher if diffusion effects are taken into consideration. Consequently, the use of the LTE formulas in plasma spectroscopy of low-current vacuum arcs is very limited.<
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