Ohm’s Law, the Reconnection Rate, and Energy Conversion in Collisionless Magnetic Reconnection

Journal Article · 09 February 2025 · Space Science Reviews

DOI: https://doi.org/10.1007/s11214-025-01142-0 · OSTI ID:2513951

Liu, Yi-Hsin  ^[1]; Hesse, Michael ^[2]; Genestreti, Kevin ^[3]; Nakamura, Rumi ^[4]; Burch, James L. ^[5]; Cassak, Paul A. ^[6]; Bessho, Naoki ^[7]; Eastwood, Jonathan P. ^[8]; Phan, Tai ^[9]; Swisdak, Marc ^[10]; Toledo-Redondo, Sergio ^[11]; Hoshino, Masahiro ^[12]; Norgren, Cecilia ^[13]; Ji, Hantao ^[14]; Nakamura, Takuma M. ^[15]

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1. Dartmouth College, Hanover, NH (United States)
2. Ames Research Center, Moffett Field, CA (United States)
3. Southwest Research Institute, Durham, NH (United States)
4. Austrian Academy of Sciences, Graz (Austria); International Space Science Institute, Bern (Switzerland)
5. Southwest Research Institute, San Antonio, TX (United States)
6. West Virginia Univ., Morgantown, WV (United States)
7. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Univ. of Maryland, College Park, MD (United States)
8. Imperial College, London (United Kingdom)
9. University of California, Berkeley, CA (United States)
10. Univ. of Maryland, College Park, MD (United States)
11. University of Murcia (Spain)
12. Univ. of Tokyo (Japan)
13. Swedish Institute of Space Physics (IRF), Uppsala (Sweden); Univ. of Bergen (Norway)
14. Princeton Univ., NJ (United States)
15. Austrian Academy of Sciences, Graz (Austria); Krimgen LLC, Hiroshima (Japan)

Magnetic reconnection is a ubiquitous plasma process that transforms magnetic energy into particle energy during eruptive events throughout the universe. Reconnection not only converts energy during solar flares and geomagnetic substorms that drive space weather near Earth, but it may also play critical roles in the high energy emissions from the magnetospheres of neutron stars and black holes. In this review article, we focus on collisionless plasmas that are most relevant to reconnection in many space and astrophysical plasmas. Guided by first-principles kinetic simulations and spaceborne in-situ observations, we highlight the most recent progress in understanding this fundamental plasma process. We start by discussing the non-ideal electric field in the generalized Ohm’s law that breaks the frozen-in flux condition in ideal magnetohydrodynamics and allows magnetic reconnection to occur. We point out that this same reconnection electric field also plays an important role in sustaining the current and pressure in the current sheet and then discuss the determination of its magnitude (i.e., the reconnection rate), based on force balance and energy conservation. This approach to determining the reconnection rate is applied to kinetic current sheets with a wide variety of magnetic geometries, parameters, and background conditions. We also briefly review the key diagnostics and modeling of energy conversion around the reconnection diffusion region, seeking insights from recently developed theories. Finally, future prospects and open questions are discussed.

• Research Organization: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
• Sponsoring Organization: National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); USDOE
• Grant/Contract Number: SC0020294
• OSTI ID: 2513951
• Journal Information: Space Science Reviews, Journal Name: Space Science Reviews Journal Issue: 1 Vol. 221; ISSN 0038-6308
• Publisher: SpringerCopyright Statement
• Country of Publication: United States
• Language: English