The Use of Numerical Simulation in the Design of the Cluster/PEACE "Top Hat" Analyzer Electron Optics

Abstract

The four-spacecraft Cluster mission was to be the first to attempt to measure space plasma gradients in three dimensions. The required accuracy of these gradient measurements poses a unique challenge to the accuracy with which the individual measurements must be carried out. In designing the electron analyzers of the PEACE(Plasma Electron And Current Experiment) instrument a design target of 1% relative accuracy between the eight electron analyzers, two on each spacecraft was set. These analyzers are of the Top Hat type of hemispherical electrostatic energy analyzer with a potential 360° field of view. To optimize the analyzer electron optics and investigate the required accuracy of fabrication it was necessary to develop a new computer simulation package. A full 3D simulation was needed to study the effects of finite manufacturing tolerances since they are not in general symmetric. Also in order to meet the scientific requirements for the performance of the analyzer it was necessary to study design parameters outside the range covered by the initial study of such analyzers by Carlson et al (1983). To achieve the accuracy with a practical use of computing time required the development of a faster computational method which is described. The comparison with laboratory calibration data shows that the desired accuracy has been achieved both in the simulation method and in the relative accuracy of the analyzers.