Author ORCID Identifier

https://orcid.org/0009-0009-5344-4338

Semester

Summer

Date of Graduation

2026

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Physics and Astronomy

Committee Chair

Christopher Fowler

Committee Co-Chair

Paul Cassak

Committee Member

Weichao Tu

Committee Member

Piyush Mehta

Abstract

Magnetic reconnection is a fundamental plasma physics process whereby a change in magnetic field connectivity drives the conversion of magnetic energy into energy of the surrounding plasma, often explosively. One of the many settings where it occurs is at the dayside magnetopause of Earth and other planets, where the magnetic field, number density, and/or temperature in the plasmas on the two sides upstream of the reconnection site are asymmetric. How the incoming magnetic energy gets partitioned into outgoing energies during asymmetric reconnection remains an outstanding question; of special interest is the fraction that gets converted into internal energy of ions and electrons. Previous satellite observations of reconnection at the dayside magnetopause suggest ion and electron temperatures increase an amount proportional to the square of the asymmetric Alfven speed (Phan et al., 2013. doi: 10.1002/grl.50917; Phan et al., 2014. doi: 10.1002/2014GL061547). A previous theoretical and numerical study (Shay et al., 2014. doi: 10.1063/1.4904203) performed a control volume analysis to quantify the energy partition in symmetric or asymmetric reconnection, and found qualitative consistency between the empirical findings and numerical data for electrons during symmetric reconnection using two-dimensional particle-in-cell (PIC) simulations. It was argued that Fermi reflection is the dominant mechanism of ion heating in antiparallel symmetric reconnection exhausts (Drake et al., 2009. DOI: 10.1029/2008JA013701), but it was only studied for symmetric reconnection. We revisit the problem of energy partition and Fermi acceleration in asymmetric reconnection and make several key advances, namely (1) in the control volume analysis, we make no assumptions about the isotropy of the pressure tensor, (2) we show that the appropriate weighting of fluxes across the control volume edges from first-principles is the number density flux, rather than the density or no weighting that has been employed previously, (3) we retain the heat flux density and the downstream Poynting flux in the control volume analysis, and (4) we generalize a past approach (Li and Liu, 2021. DOI: 10.3847/1538-4357/abf48c) that predicts the ion phase space densities in the exhaust in asymmetric reconnection as a means to quantify the ion heating. Then, we perform a PIC study of antiparallel asymmetric reconnection with different plasma and magnetic field asymmetries. Our results largely agree with the previously proposed proportionality between the squared asymmetric Alfv´en speed and the ion and electron temperature increase. The predictions for the Fermi acceleration model of ion heating in asymmetric reconnection agree well with the simulations in the scaling sense. We compare our results with previous satellite observations and symmetric simulations. Our study has important implications for planetary magnetospheres, the solar wind, and the heliospheric current sheet.

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