High velocity vapor stream in the vacuum arc

Blasts of vapor have been discovered in the last few years to issue at high velocity from the cathode region of a vacuum arc. The consideration of this subject is important in the study of the arc. Previous theories of the cathode of an arc which have not taken account of the vapor stream must be extended, for the vapor blast, as it now appears, is a part of the cathode phenomena and as such must be included in any satisfactory theory of the cathode of an arc. The energy carried away in the high velocity vapor stream, which is not an inconsiderable part of the total energy loss at the cathode, must be included in the heat balance at the cathode. This paper reviews the experimental evidence for the existence of the vapor blast, and discusses the theories proposed to explain its origin.