The factors of gradiental nonequilibrium in thermal plasmas

Electric arc plasmas are generally considered to be in local thermodynamic equilibrium (LTE) due to the high frequency of collisional processes. This point of view is predominant. For example it is typically agreed that the LTE-state takes place in the electric arc plasma in copper vapours. Nevertheless our experience has shown that this widely accepted assumption is often invalid. The state of plasma plays a key role in basic processes in an electric arc. It is very essential in the determination of the space distribution of plasma forming particles density in the arc from the results of emission spectroscopy measurements, too. That is why this paper deals with various cases of nonequilibrium due to the gradients of plasma parameters. The role of the diffusion and radiation transfer as the factors of nonequilibrium in an electric arc plasma have been investigated by spectroscopy and probe methods. The objects of study were the pulse plasma in argon and helium and the free-burning electric arc plasma between copper electrodes. Application of a pulse electric arc in a microsecond range much simplifies a problem of study, allowing division in time effects, essentially inseparable in stationary processes. The latter is to distinguish characteristic time of arc existence and the time of plasma recombination. It is well known that the properties of plasma in an electric arc between noncooling copper electrodes are determined by metallic vapours, arising from the electrodes. That is why investigation carried out is fully applicable to vacuum arcs