Collisional and Radiative Processes in Optically Thin Plasmas

Most of our knowledge of the physical processes in distant plasmas is obtained through measurement of the radiation they produce. Here we provide an overview of the main collisional and radiative processes and examples of diagnostics relevant to the microphysical processes in the plasma. Many analyses assume a time-steady plasma with ion populations in equilibrium with the local temperature and Maxwellian distributions of particle velocities, but these assumptions are easily violated in many cases. We consider these departures from equilibrium and possible diagnostics in detail

RECENT PROGRESS IN LMIS THEORY

We report on progress towards developing an improved model of liquid-metal ion source behaviour. First, we have formulated a shape condition that takes shank viscous drag effects into account, and have shown that these may affect emitter shape modelling. Second, we have concluded that further progress with the Kingham-Swanson approach requires a new shape approximation in their program. Third, we have devised a rigorous variational proof of the standard formula for the pressure difference across a charged conducting liquid surface

New understandings in the theory of liquid-metal ion sources

This paper summarises some recent improvements in our theoretical understanding of liquid-metal ion sources. (a) Some years ago it was shown how the standard formula for pressure difference across a charged conducting liquid surface could be derived directly from the laws of thermodynamics. This is now proved equivalent to the minimisation of an unfamiliar form of generalised free energy. (b) A simpler derivation of Mair's formula for LMIS current / voltage characteristics can be obtained 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 current / voltage characteristics, by incorporating a negative base-pressure into the Forbes-Ljepojevic LMIS modelling program, are reported: trends obtained are in qualitative agreement with experiment. (d) Initial results are reported from research that aims to develop a full time-dependent treatment of LMIS electrohydrodynamics. It seems that, under the combined influence of gravitational and electrostatic forces, the surface of a conducting liquid can develop into a highly disorganised state. © 1995