Undamped Oscillations of Electric Current in Coronal Magnetic Loops and in Magnetic Loop Arcades
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The possibility of the existence of undamped oscillations of the electric current in coronal magnetic loops and loop arcades due to the presence of a photospheric electromotive force arising in the base of the coronal magnetic loop as a result of the engagement of photospheric convection and the magnetic field of the loop is demonstrated. This photospheric EMF plays the part of negative resistance in the equation of the equivalent electric circuit and leads to a “soft” excitation of electric current self-oscillations. The frequency, amplitude, and phase of the oscillations have been found as functions of the electric current and supercriticality of the photospheric EMF. The possibility of the existence of self-oscillation regimes in arcades of coronal magnetic loops has been considered.
This work was supported by the Russian Science Foundation, project nos. 16-12-10448 (Sections 1 and 2), 16-12-10528 (Section 3), Russian Foundation for Basic Research, project no. 17-02-00091a, as well as by the State Contract (project no. 0035-2014-0029) and Project 14Z50.31.0007 and by the program of Presidium RAS no. 28.