Solar Orbiter's Energetic Particle Detector (EPD) - LET
SupraThermal Ion Spectrograph (SIS) identifies particles by time-of-flight (TOF) mass spectrometry. It covers the energy range from ~0.008 MeV/nucleon to 10 MeV/nucleon for He to Fe. SIS consists of two units, each with one particle telescope (sunward and antisunward) located near a single electronics box with power and data interface to the ICU. Particles are detected when they pass through the entrance foil and trigger one of the solid state detectors (SSDs) in the array in the back. Secondary electrons emitted when the ion passes through the entrance-, mid-, and detector foils are accelerated to ~1 kV and directed via isochronous mirrors onto micro-channel plates (MCPs). Fast signals from the MCPs provide Start-1, Start-2, and STOP signals that are analyzed to obtain the time-of-flight measurements for the ions. The SSD measures the residual energy of the ion. By combining the two parameters, and the known flight path of the telescope, the mass of the ion can be identified individually. SIS’s high-mass resolution (m/sm ~ 50) allows us to identify 3He/4He ratios down to <1 %. SIS is now being developed under our European lead in collaboration with Spain's SENER and the Johns Hopkins University Applied Physics Laboratory(JHU/APL).