Influence of vacuum heat treatment to the breakdown characteristic and the field electron emission characteristic of oxygen-free copper electrodes after spark conditioning

Spark conditioning procedure is widely used to improve the hold-off performance of vacuum gaps, but there are still unknown points for the mechanism of spark conditioning. Previous studies showed that both anode and cathode surfaces were cleaned by the conditioning and the cathode surface was covered with melted layer caused by the arc occurrence. In addition the field electron emission from the conditioned cathode under dc field emission test was not observed by the ampere meter having 10^-12A of minimum current sensitivity. From these previous findings we expect that the melted layer play an important role to increase the hold-off voltage and to reduce the field electron emission current. In this experiment we investigated field electron emission characteristics of electrodes processed by spark conditioning. Furthermore treatment of these electrodes with in-vacuum heating was carried out to measure the change of the field electron emission characteristics. It was confirmed that field emission electrons from the cathode processed by spark conditioning couldn´t be observed and subsequent in-vacuum heat treatment of the spark conditioned cathode caused to activate field electron emission