Helium breakdown near the critical state

Recent statistical analyses of DC breakdown data under very controlled laboratory conditions suggest that more than one breakdown mechanism may occur in liquid helium. The background of the statistical analyses and the resulting conclusions are discussed. It is shown that the splitting of the breakdown probability distributions into two collectives may indicate a real physical background. Only the low-stress collective seems to be consistent with the ideas of bubble breakdown. Low stress breakdown may be determining under technical conditions. The high-stress breakdown collectives are determined by the liquid density but not by the pressure. The tendency is similar to that found in high-density gas, with a pronounced second increase after a plateaulike region. Bubble breakdown seems not to be consistent with such a characteristic.<
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