We have reviewed the vacuum arc literature with particular emphasis on current interruption modeling. We have also set up a current counterpulse circuit, and have made preliminary measurements of plasma conditions prior to and following current zero. Finally, we have initiated analysis of both the Westinghouse data, and the data of other investigators. With respect to the literature review, we have noted the limiting models described as ''static sheath'' and ''ion matrix,'' and the intermediate models developed by Holmes and Yanabu and Childs and Greenwood. We have also noted that previous authors have had to assume an ion speed, following interruption, which is significantly less than the ion speed during steady state arcing. In order to provide additional data on plasma conditions, both prior to and following a current counterpulse, we have measured shield currents and post arc currents using a vacuum interrupter equipped with CLR electrodes. We have confirmed high post arc currents approaching 100A following the interruption of high current arcs of several thousand amperes. Furthermore, the magnitude of both the post arc current, and the total charge collected, increase significantly when the vapor condensation shield is electrically connected to the shield during the post arc period. Wemore » have related the charge collected by the electrodes, following interruption, to both the steady state current and the time for that current to reach zero.« less

Previous measurements of post-arc currents for copper-chrome electrodes have been interpreted using a model based on ion velocity changes due to momentum transfer to evaporated atoms, with subsequent collection of those ions at the new cathode. This model also takes into account the diminishing production of ions at the cathode spots during the current counterpulse. The model is consistent with present concepts of the ion flux magnitude as a fraction of the total arc current, and the ion velocity during steady state arcing. As one approach to investigating reignition, we have measured some of the parameters associated with cathode spot formation on a negatively biased shield (''cathode'') during arcing. Preliminary results indicate that input powers of approx.1 MW are associated with arcing to the shield, but it is not clear whether this breakdown is associated with thermal or electric field phenomena.