The Role of Excited Atoms on the Non-Equilibrium of Partially Ionized Plasma: Use of the Klein Effect

Realization of effective non-equilibrium ionization in low-temperature and partially- ionized plasma is one of the most important problems in direct energy conversion systems. The Klein effect, a new method of direct energy conversion to electricity, shows that collisions of the second kind, between electrons and excited atoms and molecules present in plasma, are vital in keeping the electron temperature much higher than the corresponding neutral particle and ion temperature in the working gas. This is of interest with direct energy conversion where fission reactors are the heat source, as excited atoms or molecules are produced by the various radiations and fission fragments. A closed cycle system, using either mercury vapour or argon was used for investigation of the fundamental aspects of the Klein effect, especially as it affects behaviour in the nozzle and in the regions around the electrodes. Application of the Klein effect to non reactor-bound systems was also considered. The mercury vapour circuit consisted of a boiler and superheater, a duct section comprising a nozzle and the electrodes in a magnetic field, a condenser connected to a vacuum system, and the return feed to the boiler. The mercury vapour was ionized by using either an i.f. oscillator, a d.c. discharge or electron bombardment. The behaviour and relaxation lengths of excited atoms under various operating conditions and the dependence on the energy of the bombarding electron beam were investigated. The experiments with the argon plasma jet in a stainless steel duct involved measurements of the temperatures of the gas (modified resonance reversal method) and electrons (double probe method) to explain the behaviour of the excited atoms. Some anomalies were found. (author)