Vacuum arc anode plasma. II. Collisional-radiative model and comparison with experiment

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Abstract
A one‐dimensional model describing the ionization and excitation of Al2+ ions in the anode plasma of a vacuum arc is developed using collisional‐radiative ionization and recombination coefficients. The model is constructed so that local thermodynamic equilibrium (LTE) is approached in the collision‐dominated limit; however, when the results of the model are compared with the experimental data, the anode plasma is shown not to be in LTE. The experimental and theoretical results are shown to be consistent for Ne?5×1020 m−3 and kTe/e?30 V within about 0.3 mm of the anode surface. At distances greater than 0.3 mm from the anode, kTe/eTe at Z=0.3 mm suggests that a potential ’’hump’’ exists in the anode plasma out to Z=0.3 mm. Theoretical Al2+ excited‐state densities are shown to be related by a Boltzmann factor with a ’’temperature’’ that is considerably less than and independent of the electron temperature in the plasma.

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