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

Nicolaou, G; Wicks, R; Livadiotis, G; Verscharen, D; Owen, C; Kataria, D; (2020) Determining the Bulk Parameters of Plasma Electrons from Pitch-Angle Distribution Measurements. Entropy , 22 (1) , Article 103. 10.3390/e22010103. Green open access

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Abstract

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.

Type: Article
Title: Determining the Bulk Parameters of Plasma Electrons from Pitch-Angle Distribution Measurements
Open access status: An open access version is available from UCL Discovery
DOI: 10.3390/e22010103
Publisher version: http://dx.doi.org/10.3390/e22010103
Language: English
Additional information: This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Keywords: space plasma; kappa distributions; pitch-angle distributions; plasma instruments
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics > Advanced Instrumentation Systems
URI: https://discovery.ucl.ac.uk/id/eprint/10089888
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