Presheath formation and area design limit satellite-based Langmuir probes

Abstract

In this article, the effect of 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 works have discussed electron sheath/presheath formation and the electron Bohm criterion along with their implications on the satellite-based Langmuir probes. The effects predicted by the latest theory of electron Bohm criterion were not experimentally observed and the experimental result remains supportive of a critical area ratio (AL/AS)crit = (mi/(2.3me))1/2 between the probe area AS and the satellite area AL 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 (AL/AS)crit and a Langmuir probe’s signal quality by giving additional electron current to AL. With these results, a series of limitations of maximum probe area are derived when designing satellite-based Langmuir probes, with consideration of both mission what the satellite aims and plasma where the satellite-based probe works. This series of proposed measures is 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.