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.