A theory of a cathode region of atmospheric-pressure arcs

Summary form only given. Investigations on the theory of current transfer to cathodes in high-pressure arcs may be divided into two groups, depending on the approach employed. The first group comprises studies that combine some or other model of the near-cathode plasma layer with a model of heat transfer in the cathode body. This group includes early theories and also some recent investigations. Although most of these studies were incomplete (in particular, they were unable to predict the radius of the cathode spot without using empirical parameters or rather arbitrary theoretical suppositions such as a "principle" of minimum voltage), it was believed that this approach provided a basic understanding of the relevant physics. Note that this approach is similar in its physical essence to the macroscopic approach in the theory of cathode spots in vacuum arcs. The second group comprises recent investigations in which current transfer to a cathode in a high-pressure arcs is calculated in the course of numerical modeling of the entire system arc-cathode, including the arc column, the near-cathode plasma layer and the cathode body. In the present paper the same method is employed in the framework of the first above-mentioned approach in the theory of atmospheric pressure arc spots. Physics of the near-cathode plasma layer is reconsidered with account of the above-mentioned recent contradictions. In particular, the question of a role of the near cathode space-charge sheath is discussed. It is shown that models disregarding the sheath encounter problems with electric current balance and with the energy balance. A model of the near-cathode plasma layer is discussed.