High-Spatial-resolution electron density measurements using the needle Langmuir system on different space platforms

Abstract

Electron density measurements in space and in laboratory using the multi-needle Langmuir probe (m-NLP) system have been assessed. The instrument was developed by the University of Oslo to explore multi-scale physical processes that are causing rapid variations of measured phase of satellite signals at high latitudes. This PhD project has focused on identifying and evaluating the most severe issues, e.g., spacecraft charging and wakes, that need to be accounted for in further development of the instrument including the data analysis. The m-NLP system has been demonstrated to be capable of continuously resolving small-scale plasma structures as well as monitoring the platform potential on NorSat-1. Additionally, the m-NLP system developed for the QB50 satellites has been successfully verified in the plasma chamber. Laboratory and in-situ data have validated operations of a miniaturized thermionic electron emitter, which has been previously developed to alleviate spacecraft charging effects. For small spacecraft such as the daughter payloads of the 4DSpace module, a possible solution to reduce the risk of inter-probe sheath coupling is to deploy a single fixed-bias needle probe with a high bias voltage. Besides, analysis also showed that for a needle probe as small as the m-NLP probes, the effect of surface contamination is insignificant as the probe is operating in the electron saturation region. Finally, two data analysis techniques have been studied concluding that the two approaches have advantages and disadvantages with respect to the current m-NLP implementation, and both can be applied to derive the plasma parameters.