| Abstract: |
The transport of positive and negative ions plays an important role in the initiation and behavior of discharges in gaseous dielectrics. In many cases, the identities, intensities, and kinetic energies of ions are determined by ion-molecule collisions experienced by ions as they are accelerated through the discharge. To help delineate the role of various collisional processes, such as charge-exchange collisions, collisional detachment, and ion conversion, we have measured the kinetic-energy distributions (KEDs) of positive and negative ions formed in dc Townsend discharges generated in O2 and SF6 at high electric field-to-gas density ratios (E/N). The relative abundances and mean energies of the ions are obtained from these measurements, and the effective cross sections for the ion-molecule reactions, in some cases, may be calculated. The availability of ion-molecule collision cross sections for the negative ions formed in O2 and SF6 enable a reasonable understanding of the KED data. However, for these two molecules, attempts to analyze the KED data for these two gases highlight the lack of fundamental ion-molecule cross section data for positive ions formed in these discharges. |
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