In-flight performance and preliminary observational results of Solar Wind Ion Detectors (SWIDs) on ChangʹE-1

SWIDs (Solar Wind Ion Detectors, SWID-A and SWID-B) are two of the scientific instruments on ChangʹE-1, the first Chinese lunar mission. SWIDs utilize top-hat electrostatic analyzer to measure the low energy (<20 keV/q) ion distribution of solar wind and the plasma environment around the Moon. SWIDs consist of two identical instruments with two perpendicular fan shaped field-of-views of 180°×6°. The preliminary observational results of SWIDs show that SWIDs were sufficient to measure the basic characteristics of the Moon-plasma interaction. A typical event about the Moon and solar wind interaction is discussed in this paper. Another new observational result near the Moon reported in this paper is the double proton beams coupled with a single alpha beam in solar wind. This is the first double ion beams event reported near the Moon. The double ion beams appeared having relatively anisotropic characteristics due to the interaction between solar wind and the Moon.