Abstract
Abstract. Space plasma spectrometers have often relied on spacecraft spin to collect three-dimensional particle velocity distributions, which simplifies the instrument design and reduces its resource budgets but limits the velocity distribution acquisition rate. This limitation can in part be overcome by the use of electrostatic deflectors at the entrance of the analyser. By mounting such a spectrometer on a Sun-pointing spacecraft, solar wind ion distributions can be acquired at a much higher rate because the solar wind ion population, which is a cold beam that fills only part of the sky around its mean arrival direction, always remains in view. The present paper demonstrates how the operation of such an instrument can be optimized through the use of beam tracking strategies. The underlying idea is that it is much more efficient to cover only that part of the energy spectrum and those arrival directions where the solar wind beam is expected to be. The advantages of beam tracking are a faster velocity distribution acquisition for a given angular and energy resolution, or higher angular and energy resolution for a given acquisition rate. It is demonstrated by simulation that such beam tracking strategies can be very effective while limiting the risk of losing the beam. They can be implemented fairly easily with present-day on-board processing resources.
Highlights
The plasma in the outer layers of the solar atmosphere is so hot that even the Sun’s gravity cannot restrain it
Studies of solar wind turbulence at kinetic scales require the acquisition of full three-dimensional velocity distribution functions (VDFs) with high energy resolution and high angular resolution at a rapid cadence to be able to observe various signatures of the underlying processes in the VDFs (e.g. Marsch, 2006, 2012; Kiyani et al, 2015; Valentini et al, 2016) while maintaining a sufficient signal-to-noise ratio
A third drawback is that this would make the duration of VDF acquisition variable and unpredictable, which usually is considered undesirable from the point of view of on-board instrument management
Summary
The plasma in the outer layers of the solar atmosphere is so hot that even the Sun’s gravity cannot restrain it. The BIFRAM spectrometer on Prognoz 10 used a hybrid approach, with multiple analysers simultaneously sampling along the Sun–Earth line and scanning over energy in a time-shifted way to obtain a 63 ms time resolution, and at the same time using several detectors pointing from 7 to 24◦ away from the solar direction along different azimuth angles; while not covering the full sky, combining these data leads to representative energy spectra with a time resolution of 640 ms (Vaisberg et al, 1986; Zastenker et al, 1989), a rate much faster than the spacecraft spin (118 s).
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