Aditya Solar wind Particle Experiment (ASPEX) onboard Aditya – L1:  The Solar Wind Ion Spectrometer (SWIS)

Abstract On-board India’s Aditya L1 spacecraft is the Solar Wind Ion Spectrometer (SWIS) instrument which is a part of the Aditya Solar Wind Particle Experiment (ASPEX), one of the three instruments carrying out in-situ measurements of solar wind. SWIS, comprising of two Top Hat Analyzers (THA-1 andTHA-2), is designed to measure the flux, the energy distribution and the angular distribution of primarily proton (H+ ions) and alpha (He2+ ions) particles in the energy range of 0.1–20 keV with 360◦ angular coverage in two planes, the ecliptic plane and in the plane perpendicular to it. Based on SWIS observations, it will be possible to address variations in the flux of protons and alpha particles in the ambient solar wind and in transient structures like Interplanetary Coronal Mass Ejections (ICME), Stream Interaction Regions (SIR) passing through the spacecraft location. Over the life of the mission the multi-directional observational capabilities of SWIS are expected to provide valuable data on the variations in the primary composition of solar wind, its velocity distribution and directional anisotropy. The SWIS instrument will also capture the low energy end of the suprathermal population in the solar wind. These measurements are expected to pave the way to better understand the relationship between the solar wind and suprathermal population in the solar wind under varying inter-planetary conditions. This article describes the design and calibration aspects of the instrument and reports preliminary observations from the SWIS instrument.