NEW UNDERSTANDINGS IN THE THEORY OF LIQUID-METAL ION SOURCES

This paper summarises some recent improvements in our theoretical unde rstanding of liquid-metal ion sources. (a) Some years ago it was shown how the standard formula for pressure difference across a charged con ducting liquid surface could be derived directly from the laws of ther modynamics. This is now proved equivalent to the minimisation of an un familiar form of generalised free energy. (b) A simpler derivation of Mair's formula for LMIS current/voltage characteristics can be obtaine d by applying Newton's Second Law to the motion of the liquid cone as a whole. (c) Results of modelling the effect of viscous drag on LMIS c urrent/voltage characteristics, by incorporating a negative base-press ure into the Forbes-Ljepojevic LMIS modelling program, are reported: t rends obtained are in qualitative agreement with experiment. (d) Initi al results are reported from research that aims to develop a full time -dependent treatment of LMIS electrohydrodynamics. It seems that, unde r the combined influence of gravitational and electrostatic forces, th e surface of a conducting liquid can develop into a highly disorganise d state.