Observation of field emission behavior on cathode surface

A field emission from metal surface is known to play a dominant role of a breakdown in vacuum. We observed the field emission electrons and its emission sites on the cathode surface by using a micro channel plate (MCP) with a luminescent screen under the high vacuum condition. A CCD camera observed location of emission sites and its change with time. By using a computer analysis, the change of emission sites with time at each 16 m second could be observed. As a result, it was found that appearance and disappearance of emission sites was repeated in a short time less than 0.1 s, however, the number of emission sites counted in an observation was kept constant. It was seemed that the fluctuation of emission current was related to the disappearance of emission sites. This observation of field emission revealed that almost emission sites could sustain an electron emission for no longer than 0.1 sec. It was estimated that the chemical or geometrical changes were occurred at emission site by electron emission