Numerical Simulation of the Geometric Factor of a Cylindrical Electrostatic Analyzer to Monitor Electron Precipitation in the South Atlantic Magnetic Anomaly

Abstract

This paper simulates the performance of a cylindrical electrostatic analyzer specially devised to measure the energy spectra of electrons precipitating in the South Atlantic Magnetic Anomaly (SAMA). Unlike its counterparts built to operate in the auroral region, the dimensions of this analyzer were designed to maximize the geometric factor, and to be the first experiment dedicated to measure the much lower fluxes in the equatorial ionosphere. The geometric factor of the analyzer was calculated based on the numerical simulation of electron trajectories coming from a calibration beam using the package SIMION 8.0. Positive and negative voltages applied to the inner and outer plates were compared to examine the analyzer’s response, showing small but visible differences. Simulations at the lower and higher ends of the energy spectrum showed similar geometric factors [ $G$ ] as expected with $[G]/E_{\mathrm {peak}} \sim 2.9\times 10^{\mathrm {-3}}$ (cm $^{2}\cdot {\mathrm{ sr}}$ ) and $\Delta E/E_{\mathrm {peak}} \sim 0.29$ . These results are in good agreement with semianalytical and empirical estimates. Comparisons with two analyzers designed for measurements in the auroral region showed that the simulated geometric factors are about one order of magnitude larger. Flux estimates based on aeronomic effects over the SAMA indicate that the number of counts should be sufficiently above noise level with the present analyzer design.