Woodliffe, Roger David; (1991) Design of space plasma analysers by computer simulation. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The Top Hat electron analysers on board the four spacecraft of the CLUSTER mission will break new ground in space plasma research by measuring plasma gradients between spacecraft and measuring very low energy electrons (~ 0.7eV). These mission aims require the analysers axe made as nearly exactly the same as possible to enable accurate gradient measurements and that the analysers be designed such that secondary electron contamination of the low energy measurements is kept to a minimum. In this thesis these analysers are designed and analysed using a variety of computer simulations. The basis of these simulations is a finite difference solution to the electric potential followed by trajectory tracing electrons through the analyser. Comparison of these simulations with experimental calibration data show a large difference between the results. Analysis of the manufacturing process reveals that there is a possibility of a large hemisphere non-concentricity due to a build up of tolerances from individual analyser components which may effect the analyser response. This effect on the response is proved using a 3-D non-concentric analyser simulation which explains the discrepancy observed and shows how accurately the analysers must be made so that the analysers can acquire sufficiently accurate data. It is proved using a hemispherical plate analyser that secondary electron emission poses a serious threat to low energy electron measurements by spherical plate type analysers. A 3-D secondary electron emission and trajectory tracing simulation is designed which enables the problem created by contamination of low energy measurements by secondary electrons to be greatly reduced. Utilising a prior knowledge of the underlying structure of the Top Hat response function a new method of determining the band-pass of Top Hat analysers is designed which is approximately an order of magnitude faster than conventional methods and allows such analysers to be characterised much more easily.

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