Combined spatial and temporal measurements of ionization growth in nitrogen have enabled the secondary ionization effect due to N2(A3 Sigma u+) metastable molecule impact on the cathode to be separated from the overall ionization growth data. The residual data have been analysed by standard methods to give accurate values of the primary ionization coefficient alpha /N within the range E/N=140-3400 Td (1 Td identical to 10-17 V cm-2). This range has been extended down to 85 Td by application of an indirect procedure based on improved knowledge gained from the secondary ionization measurements in nitrogen and their dependences on E/N. The measurements have been able to separate the secondary ionization coefficient into a fast (photon and positive ion) component and a slow (metastable molecule) component.

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An expression is obtained for the first Townsend ionization coefficient in uniform crossed electric and magnetic fields, and shown to be in better agreement with observation than previous theoretical expressions. The" equivalent pressure" concept for the effect of a transverse magnetic field on this coefficient is shown to be a valid approach to the problem, although the value for the equivalent pressure obtained in this analysis differs from the values given by earlier authors.

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