Abstract
In-situ measurements of space plasma throughout the solar system require high time resolution to understand the plasma’s kinetic fine structure and evolution. In this context, research is conducted to design instruments with the capability to acquire the plasma velocity distribution and its moments with high cadence. We study a new instrument design, using a constant magnetic field generated by two permanent magnets, to analyze solar wind protons and α-particles with high time resolution. We determine the optimal configuration of the instrument in terms of aperture size, sensor position, pixel size and magnetic field strength. We conduct this analysis based on analytical calculations and SIMION simulations of the particle trajectories in our instrument. We evaluate the velocity resolution of the instrument as well as Poisson errors associated with finite counting statistics. Our instrument is able to resolve Maxwellian and κ-distributions for both protons and α-particles. This method retrieves measurements of the moments (density, bulk speed and temperature) with a relative error below 1%. Our instrument design achieves these results with an acquisition time of only 5 ms, significantly faster than state-of-the-art electrostatic analyzers. Although the instrument only acquires one-dimensional cuts of the distribution function in velocity space, the simplicity and reliability of the presented instrument concept are two key advantages of our new design.
Highlights
We neglect any relative drifts between α-particles and protons, since these are small compared to their bulk speeds in the solar wind and would not affect our result significantly
Our instrument concept Magnetic Plasma Analyzer (MPA) aims at answering science questions on small-scale processes that are generally believed to be important for the solar-wind heating and acceleration
We study the ability of a magnetostatic plasma instrument to resolve proton and α-particle velocity distribution functions (VDFs) with a high time resolution
Summary
The solar wind is a plasma flow, emitted by the Sun, that fills the entire heliosphere. Sci. 2020, 10, 8483 any space-plasma instrument must resolve non-thermal properties of the particle VDFs. as the solar wind passes over the measurement point at a supersonic speed (approximately in the range from 300 to 800 km/s) in the spacecraft frame, the acquisition of VDF variations must be achieved with high cadence. Modern space plasma instrumentation aims at sampling the VDF with a high enough cadence to study sub-ion-scale variations in the VDF. This is the direction taken by, for example, the Debye mission [10] and the THOR mission [11]. The goal of our instrument design is a cadence of 5 ms, which is two orders of magnitude faster than the requirement to resolve structures with a size of the average ρ p at a heliocentric distance of 1 au
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