Nonequilibrium Characteristics of the Working Plasmas for Magnetoplasmadynamic (MPD) Generators

抄録

The possible nonequilibrium ionization in an MPD generator is theoretically described. A generalized Saha equation is derived and found to be different from that based on the electron temperature, when the electron temperature is slightly higher than the gas temperature. The effective elastic collision loss factor is larger than 2, due to the de-excitational radiation at lower electron temperatures or due to the recombinational radiation at higher temperatures. The theory reasonably explains the current-electric field characteristic and other nonequilibrium characteristics experimentally obtained. The value of the peak in the electric field appearing in the above characteristic is determined; this peak does not appear in the atmospheric helium seeded with cesium, at gas temperatures ≥1500°K or at initial electron densities \gtrsim10¹⁶ m³. It is given why the nonequilibrium ionization is not produced when the generators are operated at low gas temperature.