Presheath formation and area design limit satellite-based Langmuir probes

In this article, the effect of the finite conductive surface area of a satellite on the use of satellite-based Langmuir probes is reviewed in light of the basic theory of asymmetric double Langmuir probes (ADLPs). Recent theoretical and experimental studies have discussed electron sheath/presheath formation and the electron Bohm criterion along with their implications for satellite-based Langmuir probes. The effects predicted by the latest theory of the electron Bohm criterion were not experimentally observed and the experimental results remain supportive of a critical area ratio (A L/A S)crit = (m i/(2.3m e))1/2 between the probe area A S and the satellite area A L as conventionally believed. A satellite-based Langmuir probe must satisfy this criterion to physically act as a single Langmuir probe. However, experimental investigations also found that high-energy electrons adversely affect (A L/A S)crit and a Langmuir probe's signal quality by giving additional electron current to A L. Based on these results, a number of limitations of the maximum probe area are derived when designing satellite-based Langmuir probes, with consideration of both the aim of the satellite and the plasma where the satellite-based probe works. These proposed measures are expected to only partially alleviate the effect of the inadequate satellite surface area on the application of satellite-based Langmuir probes. Using a larger satellite to carry a Langmuir probe remains the most viable means to obtain precise space plasma parameters.

Automated summary

This article reviews the effect of the finite conductive surface area of a satellite on the use of satellite-based Langmuir probes. The theoretical and experimental studies discussed the formation of electron sheath/presheath and the electron Bohm criterion. The experimental results supported the conventional belief that the critical area ratio between the probe area and the satellite area must be satisfied for a satellite-based Langmuir probe to function properly. However, it was also found that high-energy electrons negatively affect this criterion and the signal quality of the Langmuir probe. Design limitations for satellite-based Langmuir probes are proposed based on these findings. Using a larger satellite remains the most viable option for obtaining precise space plasma parameters.