Thermal Energy Budget of Electrons in the Inner Heliosphere: Parker Solar Probe Observations

Abraham, Joel B., Verscharen, Daniel, Wicks, Robert, Agudelo Rueda, Jeffersson A., Owen, Christopher J., Nicolaou, Georgios and Jeong, Seong-Yeop (2022) Thermal Energy Budget of Electrons in the Inner Heliosphere: Parker Solar Probe Observations. The Astrophysical Journal, 941 (2). p. 145. ISSN 0004-637X

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We present an observational analysis of the electron thermal energy budget using data from Parker Solar Probe. We use the macroscopic moments, obtained from our fits to the measured electron distribution function, to evaluate the thermal energy budget based on the second moment of the Boltzmann equation. We separate contributions to the overall budget from reversible and irreversible processes. We find that an irreversible thermal energy source must be present in the inner heliosphere over the heliocentric distance range from 0.15 to 0.47 au. The divergence of the heat flux is positive at heliocentric distances below 0.33 au, while beyond 0.33 au, there is a measurable degradation of the heat flux. Expansion effects dominate the thermal energy budget below 0.3 au. Under our steady-state assumption, the free streaming of the electrons is not sufficient to explain the observed thermal energy density budget. We conjecture that the most likely driver for the required heating process is turbulence. Our results are consistent with the known nonadiabatic polytropic index of the electrons, which we measure as 1.18 in the explored range of heliocentric distances.

Item Type: Article
Additional Information: Funding information: J.B.A. is supported by the Science and Technology Facilities Council (STFC) grant ST/T506485/1. D.V. is supported by the STFC Ernest Rutherford Fellowship ST/P003826/1. C.J.O and D.V. receive support from the STFC Consolidated Grants ST/S000240/1and ST/W001004/1. R.T.W. is supported by STFC Consolidated Grant ST/V006320/1. J.A.A.R. is supported by NASA grant 80NSSC21K2048 and NSF grant 2142430. S.-Y.J. is supported by STFC grant ST/W000369/1.
Subjects: F300 Physics
F500 Astronomy
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: John Coen
Date Deposited: 20 Dec 2022 08:54
Last Modified: 20 Dec 2022 09:00

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