Studies of total ionization in gases/mixtures of interest to pulsed power applications

摘要

The energy required to produce an electronhyphen;ion pair (i.p.),W, for the agr;hyphen;particle irradiated gases CF4, C2F6, C3F8, andnhyphen;C4F10has been measured and found to be 34.3, 34.5, 34.4, and 34.2 eV/ i.p., respectively. The large values ofWfor these perfluorocarbons (PFCs) are attributed to their large cross sections for electron impacthyphen;induced dissociation. The constancy ofWfor this group of molecules is discussed with respect to the constancy of the ratio (sim;0.68) of the respective (energy integrated) total ionization cross section to the total (energy integrated) inelastic scattering cross section.Wvalues are also reported for the binary gas mixtures Ar/CF4, Ar/C2F6, Ar/C3F8, and CH4/CF4which have conduction and insulation properties suitable for use in diffuse discharge opening switches. TheWvalues for these binary mixtures (and for C2H2/CF4, C2H2/C2F6, and C2H2/C3F8) increase with the amount of PFCs in the mixture and (contrary to the Ar/C2H2mixture) exhibit no Jesse effect. The ternary gas mixtures Ar/C2H2/PFC (=CF4, C2F6, C3F8) containing lsim;10percnt; PFC were found to exhibit a pronounced Jesse effect which is a function of the content of the PFC in the mixture and the electron scattering cross section of the PFC itself. Substantial increases in ionization can be achieved by adding to the Ar/PFC binaries 1ndash;3percnt; of C2H2. An analysis of theWdata yielded information on the partition of the agr; particlersquo;s energy among the gas components and indicated that the rate constant for energy transfer from excited argon atoms (Arast;) to the PFC is smaller than that from Arast; to C2H2; it showed, also, that the rate constant for energy transfer from Arast; to C2H2is sim;104larger than that for collisional deexcitation of Arast; by groundhyphen;state Ar atoms. The quantitative measurements reported herewith and the parameters deduced from a simple modeling of the data permit the tailoring of ternary gas mixtures with substantial current increases over those achieved in the binary Ar/PFC (=CF4, C2F6, C3F8) mixtures which possess the desirable conduction and insulation characteristics for pulsed power opening switches.