Space plasma measurements with ion instruments

In this article we examine the factors which affect the determination of the plasma bulk parameters in space, with particular emphasis on the density determination. We make this assessment with reference to a particular instrument, the AMPTE‐UKS ion instrument, in order to be specific, but the issues raised here are likely to be encountered in the use of any space plasma instrument containing electrostatic energy analyzers or microchannel plate detectors. We have established a mathematical formalism for determining these parameters by relating the measured counts to the distribution function in terms of the geometric factor. The geometric factor is determined in the calibration of the instrument which is described in some detail. Among the factors we have considered are our calibration techniques, MCP efficiency, detector energy, and angular resolution, as well as the approximations used in our mathematical formalism. To establish confidence in our determination, we used a computer simulation to look for ...