Efflux of Atoms From Cathode Spots of Low-Pressure Mercury Arc

Abstract

A novel measuring technique was devised for the determination of the rate at which particles are ejected from the cathode spots of a low‐pressure arc. The measurements were performed with anchored spots in a low‐pressure steady‐state mercury discharge. During arc operation, the total efflux of mercury from the cathode is composed of (i) the atoms which evaporate from the spot‐free mercury surface and (ii) the particles which are ejected in connection with the cathode spots. The method applied permits a separation of these two contributions, thus yielding more accurate results than reported in the literature so far. From these measurements an electron ‐to‐atom emission ratio of 208±12 was derived for the contribution from the cathode spots, corresponding to a ratio of emitted mass to emitted charge of (9.99±0.06)×10⁻⁶ g/C.