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Determining the Bulk Parameters of Plasma Electrons from Pitch-Angle Distribution Measurements

1
Department of Space and Climate Physics, Mullard Space Science Laboratory, University College London, Dorking, Surrey RH5 6NT, UK
2
Southwest Research Institute, San Antonio, TX 78238, USA
3
Space Science Center, University of New Hampshire, Durham, NH 03824, USA
*
Author to whom correspondence should be addressed.
Entropy 2020, 22(1), 103; https://doi.org/10.3390/e22010103
Received: 30 December 2019 / Revised: 10 January 2020 / Accepted: 11 January 2020 / Published: 16 January 2020
(This article belongs to the Special Issue Theoretical Aspects of Kappa Distributions)
Electrostatic analysers measure the flux of plasma particles in velocity space and determine their velocity distribution function. There are occasions when science objectives require high time-resolution measurements, and the instrument operates in short measurement cycles, sampling only a portion of the velocity distribution function. One such high-resolution measurement strategy consists of sampling the two-dimensional pitch-angle distributions of the plasma particles, which describes the velocities of the particles with respect to the local magnetic field direction. Here, we investigate the accuracy of plasma bulk parameters from such high-resolution measurements. We simulate electron observations from the Solar Wind Analyser’s (SWA) Electron Analyser System (EAS) on board Solar Orbiter. We show that fitting analysis of the synthetic datasets determines the plasma temperature and kappa index of the distribution within 10% of their actual values, even at large heliocentric distances where the expected solar wind flux is very low. Interestingly, we show that although measurement points with zero counts are not statistically significant, they provide information about the particle distribution function which becomes important when the particle flux is low. We also examine the convergence of the fitting algorithm for expected plasma conditions and discuss the sources of statistical and systematic uncertainties. View Full-Text
Keywords: space plasma; kappa distributions; pitch-angle distributions; plasma instruments space plasma; kappa distributions; pitch-angle distributions; plasma instruments
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Nicolaou, G.; Wicks, R.; Livadiotis, G.; Verscharen, D.; Owen, C.; Kataria, D. Determining the Bulk Parameters of Plasma Electrons from Pitch-Angle Distribution Measurements. Entropy 2020, 22, 103.

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