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Split Process of Low‐Pressure Arc Cathode Spots on SS400(Fe + C) Surface with Oxide Layer

A remarkable characteristic of a cathode spot of a low‐pressure arc is that the cathode spot moves around on the metal surface. A cathode spot can remove an oxide layer. Cathode spots of low‐pressure arcs have been used for cleaning metal oxide surfaces. However, the influence of an oxide layer on the cathode spot movement remains unclear. As described herein, the cathode spot movements on the oxide layer surface and on the metal surface were measured to determine the cathode spot movement. Experiments were performed using an SS400 cathode and a cylindrical copper anode. A high‐speed video camera recorded the cathode spot movement. Then the obtained images were analyzed using plasma image processing. The cathode spot movement was generated mainly on the boundary layer, but sometimes on the processed surface. The first spot remains at the boundary when the cathode spot splits; the second spot moves on the bulk surface and reappears at a different boundary. Therefore, the cathode spot does not appear suddenly; instead, it moves continuously during the splitting process. The oxide layer serves an important role for cathode spot existence because of oxide layer vaporization. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.