Deviation from local thermal equilibrium in an atmospheric argon arc plasma

The electron temperature T/sub e/ is obtained from five optically non-thin Ar I line-transitions. It is possible to measure T/sub e/ without any knowledge of transition probabilities. The electron density N/sub e/ can be calculated from measured excited level densities using the partial LTE model. It appears that there is a functional dependence of N/sub e/ on T/sub e/, suggesting that transport processes are of only minor importance. The deviations from LTE can be described by assuming a N/sub e/-dependent overpopulation of the ground level of Ar I. This overpopulation factor varies from 1.9 for N/sub e/=2*10/sup 16/ cm/sup -3/ to 1.25 for N/sub e/=2*10/sup 17/ cm/sup -3

Unipolar arc model

A three-dimensional description of an axisymmetric unipolar arc discharge is given. Both sheath and plasma ball effects are taken into account. The analysis is based on the simultaneous solution of Ohm's law, Maxwell equations, and the boundary conditions for the electric potential at the plasma-sheath interface. These boundary conditions are dictated by the sheath effects. The potential distribution, current distribution, and magnetic fields in the plasma have been determined for a given electron density profile. These calculations show that the unipolar arc arises as a natural consequence of the pressure force

Continuous emission, lowering of the ionization potential and total excitation cross-sections of an atmospheric thermal plasma

The authors present a Partial LTE (PLTE) model in which the ground state is overpopulated with respect to the other excited states. The relative overpopulation of the ground state as a function of the electron temperature, T/sub e/, is fairly sensitive to small variations in both the transition probability, A, and the value for the lowering of the ionisation potential, Delta chi /sub 0/. The total cross-section for excitation from the neutral ground state was derived from the measured degree of overpopulation. The authors calculated the emissivity of the free-bound UV recombination radiation, which proved to be quite large in the 70-80 nm spectral range. Some results for the continuum radiation and for the Stark parameters at lambda approximately=700 nm were also give