Aditya Solar Wind Particle Experiment on Board Aditya–L1: The Supra-Thermal and Energetic Particle Spectrometer

Abstract

Aditya–L1, the first dedicated Indian solar mission, was launched on 02 September 2023 and has been placed in a halo orbit around the first Lagrange point (L1) of the Sun-Earth system on 06 January 2024. Aditya Solar wind Particle EXperiment (ASPEX) is one of the three in situ science experiments on board the Aditya–L1 mission that provides measurements of primarily protons and alpha particles in the solar wind, suprathermal, and energetic particles in the energy range from 100 eV to 6 MeV/nucleon. ASPEX consists of two independent spectrometers: the Solar Wind Ion Spectrometer (SWIS: 100 eV – 20 keV) and Supra Thermal and the Energetic Particle Spectrometer (STEPS: 20 keV/nucleon – 6 MeV/nucleon). In this article, we provide the details of the STEPS configuration, ground calibration, and in–flight performance. After the launch of Aditya–L1, two STEPS units were switched–on during the Earth-bound phase on 10 September 2023. STEPS has carried out measurements in the Earth-bound orbit for altitudes \(\gtrsim 8\) R_E, and also in the cruise phase from the Earth to the halo orbit, and has been continuously operational after insertion to the L1 orbit. The performance of STEPS is as expected during all the phases of the mission so far and all its observations are found to be consistent with similar measurements from other contemporary instruments at the L1 point.