A FARADAY-CUP SOLAR WIND EXPERIMENT FOR SOLAR ORBITER

摘要

We propose a design for a Faraday Cup instrument that could perform rapid measurements of solar wind hydrogen and helium on Solar Orbiter. Considering the instrument requirements described in the straw man payload, a Faraday Cup has many virtues in comparison with other instrument designs. First, the Faraday Cup is not sensitive to contamination. Second, the detector (a metal collector plate) is insensitive to radiation and photons. This will be a very significant factor for Solar Orbiter. Experience with the Faraday Cup system onboard the Wind spacecraft has shown a drift in the absolute response of the instrument of less than 0.1% per decade. That stability is ideal for an instrument on a spacecraft operating alone in a harsh environment. Third, the Faraday Cup would have a wide-angular acceptance (45° half-angle cone). This would enable accurate measurements of Alfven wave fluctuations. Finally, the Faraday Cup has a demonstrated track record of accurate measurements of ion beams and temperature anisotropies that have led to new scientific understanding of the instabilities that will be a key part of Solar Orbiter. We propose a Faraday Cup that would make rapid, 10-Hz measurements of three-dimensional properties of solar wind hydrogen and helium: velocities, temperatures, heat fluxes, beams, and anisotropies. A subset of these data would be sent to Earth, but the high time resolution measurements would be correlated on board with measurements of the local electric field, leading to a new understanding of the physics of dissipation and heating in the solar wind.