Low temperature plasma: fundamentals to commercial applications

Full text: This paper provides an overview of some selected aspects of low temperature plasmas that have been relevant to the wide variety of activities undertaken at Lucas Heights. Reference will be made to some early fundamental studies of weakly ionized plasmas. These investigations provided reliable, new and precise information about the spatial and temporal growth of ionization in both static electric fields and combined electric and magnetic fields. The ionization behaviour was determined essentially by electron, ion and photon processes in pure molecular gases but when investigations were extended to a study of the influence of trace impurities on the ionization behaviour, dramatic new influences were revealed. Removal of the impurities demonstrated the influence of excited neutral metastable particles. These are not influenced by electric or magnetic fields but are controlled by the process of diffusion and exert strong effects at metal surfaces. Studies of these metastable particle influences proved to be important in developing new lasers, e g. the high power excimer laser which operates in mixtures of inert gases. Most recently considerable interest has developed in the role played by similar metastable particles in plasmas established in molecular nitrogen. The role of metastable particles generated in pure nitrogen is now being examined exhaustively because strong evidence has emerged that they play an important role in commercial plasma nitriding. The latest developments emerging from the co-operative studies by ANSTO, AINSE and the University of New England have yielded new information and further investigations are continuing