Spacecraft Potential Control by the Plasma Source Instrument on the POLAR Satellite

摘要

Observations clearly demonstrate that the PSI has had the desired effect on the TIDE measurements: Low-energy ions that would otherwise be unobservable are seen. Equally clear is that the PSI modifies the sheath structure around the POLAR spacecraft in ways that also affect measurements made by other instruments, such as the PWI and the EFI. This implies that it will also have quantitative consequences for the TIDE observations. The EFI observations suggest that the TIDE core ion measurements will not be significantly affected unless ion energies are much less than 5 eV. Core electrons are more affected by the PSI sheath, and at lower outflow speeds the ions will also be influenced, requiring a better understanding of the sheath. A physical model has been presented that explains qualitatively the origin of the anisotropy found in observations with the PSI operating. This model can be used to guide the development of a detailed and accurate numerical model, which in turn can be used to develop modifications to the analysis to compensate for the PSI effects. The best understanding of the PSI sheath will come from synoptic operations of the PSI and dedicated analysis of the complete POLAR plasma data set.