Abstract:
The Solar Wind Ion Spectrometer (SWIS) instrument is a part of the Aditya Solar Wind Particle Experiment (ASPEX), one of the three in situ observation instruments on board India’s Aditya-L1 spacecraft. SWIS comprises two Top-Hat analysers (THA-1 and THA-2), which have a 360∘ angular coverage in the ecliptic plane and in the plane perpendicular to the ecliptic plane, respectively, with opening angles of . Both are electrostatic scanning instruments designed to measure the flux, the energy distribution and the angular distribution of the solar wind particles, covering the energy range of 0.1 – 20.0 keV with a 5 s cadence and 8% energy resolution. THA-1 has an additional species separation capability, based on a magnetic mass analyser (MMA) primarily designed to separate H+ and He2+, giving us the ability to measure the energy-, angle-, and time-dependent variation of the all-important helium abundance ratio in the ambient solar wind and in transient structures like interplanetary coronal mass ejections (ICME), stream interaction regions (SIR) passing through the location of the spacecraft. Over the life of the mission, the multidirectional observational capabilities of SWIS are expected to provide valuable data on the variations in the primary composition of solar wind, its velocity distribution, and its directional anisotropy. The SWIS instrument will also capture the low-energy end of the supra-thermal population in the solar wind. A special feature of the instrument is its user-level configurability for specific studies. The instrument will generate detailed information on helium abundance, its variability, and its connection to the solar wind speed.