Solar probe fast imaging plasma spectrometer

Abstract

We describe an instrument which maps charged particles of the solar wind plasma onto the entrance plane of a carbon-foil time-of-flight mass spectrometer. The field of view of the instrument is almost 2π. The entrance system is designed to resolve energy-per-charge ratios of electrons, protons, He 2+ and other solar wind ions with 5% resolution up to more than 20 keV/e. Applying position sensing micro-channelplate detectors at the beginning and at the end of the time-of-flight section allows a complete measurement of the angular distribution of the plasma flow for both electrons and ions with a time resolution of one second. The micro channel-plates are also used to generate start and stop signals. An acceleration path between the entrance system and the time-of-flight section assures a high sensitivity of the time-of-flight sensor. The sensitive parts of the instrument are protected against ultraviolet and particle radiation from the sun by both the spacecraft shield and by shields in front of the energy analyzer. The charged particles pass these shields through collimators. The instrument is budgeted to a weight of only 2 kg and a power consumption of less than 2 W. Simulations of the instrument response based on experiences with similar time-of-flight mass spectrometers (ACE, SOHO, ULYSSES, WIND) are presented.