Abstract
Abstract Spacecraft observations allow us to reconstruct the velocity distributions of space plasmas, which fully describe the kinetic state of the plasma. Space plasmas often exist in stationary states out of equilibrium, which are typically described by kappa distributions. Thus, the kappa index and temperature that govern these distributions are parameters that need to be determined for a full and accurate description of these plasmas. In this study, we demonstrate a novel and reliable way to determine the kappa index and temperature of plasma distribution functions constructed from counts observed in a narrow energy range by typical electrostatic sensors. Our method applies to cases in which the high-energy tail of the plasma is observed with significant uncertainty, or not observed at all. For the validation of our method, we produce pseudo-observations for typical input plasma parameters, specifically considering the design of the ion plasma instrument SWA-PAS on board the Solar Orbiter mission. Our method reliably estimates the relevant plasma parameters by fitting the angular spread of the distribution in a narrow energy range around the core bulk energy. We compare the output of our technique with the input parameters used to generate artificial data for a selected range of the kappa index and the temperature, and for a bulk energy typical for the solar wind. In addition, we study the effects of Poisson errors on the instrument’s counting statistics, test our method against Helios 2 measurements, and discuss its potential applications and limitations.
Highlights
ISSN 1538-4357Link: Northumbria University has developed Northumbria Research Link (NRL) to enable users to access the University’s research output
Space plasmas have been observed for decades in many different regions of space, with a wide range of different conditions
Instruments designed to sample the plasma velocity distribution generally record the count rates for particles arriving at the instrument in a given mass, energy, and angular range
Summary
Link: Northumbria University has developed Northumbria Research Link (NRL) to enable users to access the University’s research output. Single copies of full items can be reproduced, displayed or performed, and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided the authors, title and full bibliographic details are given, as well as a hyperlink and/or URL to the original metadata page. Full items must not be sold commercially in any format or medium without formal permission of the copyright holder. The full policy is available online: http://nrl.northumbria.ac.uk/policies.html. This document may differ from the final, published version of the research and has been made available online in accordance with publisher policies.
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