Abstract
No smoke without a fire, and no magnetic field without a current somewhere in the plasma permeated by the magnetic field. Ampère’s equation intimately ties the magnetic field to the current density. In astronomy, the observable parameter is the magnetic field, and currents can be inferred only indirectly. Yet, in everyday life we generally ignore magnetic fields and are more used to the concept of currents describing, for instance, how energy is transported and released in an electric circuit. Currents in coronae do not flow exclusively in well-defined channels, and the circuit analogy is of limited value. In ideal MHD (infinite conductivity, Chapter 3), currents are considered a secondary product of the magnetic field having a non-vanishing curl. Nevertheless, currents in coronae represent large amounts of free energy and are of great interest.
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Further Reading and References
Currents in plasma
Alfvén, H.: 1981, Cosmic Plasma, D. Reidel. Dordrecht, Holland.
Foukal, P. and Hinata, S.: 1991, ‘Electric Fields in the Solar Atmosphere: A Review’, Solar Phys. 132, 30.
Huba, J.: 1985, in IAU Symp. 107, ‘Unstable Current Systems and Plasma Instabilities in Astrophysics’ (eds. M.R. Kundu and G.D. Holman), D. Reidel, Dordrecht, Holland, p. 315.
Knoepfel, H. and Spong, D.A.: 1979, ‘Runaway Electrons in Toroidal Discharges’, Nuclear Fusion 19, 785.
Morrison, P.J. and Ionson, J.A.: 1982, ‘Temperature Gradient and Electric Field Driven Electrostatic Instabilities’, Phys. Fluids 25, 1183.
Papadopoulos, K.: 1977, ‘A Review of Anomalous Resistivity for the Ionosphere’, Rev. Geophys. Sp. Sci. 15, 113.
Acceleration and heating by currents
Benz, A.O.: 1987, ‘Acceleration and Energization by Currents and Electric Fields’, Solar Phys. 111, 1.
Holman, G.D.: 1985, ‘Acceleration of Runaway Electrons and Joule Heating in Solar Flares’, Astrophys. J. 293, 584.
Radiation of low-frequency turbulence
Benz, A.O. and Wentzel, D.G.: 1981, ‘Coronal Evolution and Solar Type I Radio Bursts: An Ion-acoustic Wave Model’, Astron. Astrophys. 94, 100.
Kai, K., Melrose, D.B., and Suzuki, S.: 1985, in Solar Radiophysics, (eds. D.J. McLean and N.R. Labrum), Cambridge University Press, Chapter 16 on noise storms.
Reconnection and current sheets
Heyvaerts, J., Priest, E.R., and Rust, D.M.: 1977, ‘An Emerging Flux Model for the Solar Flare Phenomenon’, Astrophys. J. 216, 123.
Priest, E.R.: 1982, ‘Solar Magnetohydrodynamics’, D. Reidel, Dordrecht, Holland.
Priest, E.R.: 1985, ‘The Magnetohydrodynamics of Current Sheets’, Rep. Prog. Phys. 48, 955.
Priest, E.R. and Forbes, T.: 1986, ‘New Models for Fast Steady State Magnetic Reconnection’ J. Geophys. Res. 91, 5579.
Reference
Hagyard, M.J.: 1988, ‘Observed Nonpotential Magnetic Fields and the Inferred Flow of Electric Currents at a Location of Repeated Flaring’, Solar Phys. 115, 107.
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© 1993 Springer Science+Business Media Dordrecht
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Benz, A. (1993). Electric Currents. In: Plasma Astrophysics. Astrophysics and Space Science Library, vol 184. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-2064-7_9
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DOI: https://doi.org/10.1007/978-94-011-2064-7_9
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