Experimental studies of the magnetic structure and plasma dynamics in current sheets (a review)
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IED PHYSICS
Experimental Studies of the Magnetic Structure and Plasma Dynamics in Current Sheets (a Review) A. G. Frank* and N. P. Kyrie** Prokhorov General Physics Institute, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected] **e-mail: [email protected] Received September 21, 2015
Abstract—Based on measurements of magnetic fields in current sheets, spatial distributions of the electric current and electrodynamic forces in successive stages of the sheet evolution are determined. Two new effects manifesting themselves mostly in the late stages of the current sheet evolution have been discovered, namely, expansion of the current flow region at the periphery of the sheet and the appearance of a region with inverse currents, which gradually expands from the periphery toward the center of the sheet. Using spectroscopic methods, generation of superthermal plasma flows accelerated along the sheet width from the center toward the periphery has been revealed and investigated. The measured energies of accelerated plasma ions satisfactorily agree with the Ampère forces determined from magnetic measurements. The excitation of inverse currents additionally confirms the motion of high-speed plasma flows from the center of the current sheet toward its side edges. DOI: 10.1134/S1063780X1706006X
1. INTRODUCTION According to current knowledge, the variety of flare phenomena, such as flares in the Sun and stars, substorms in the magnetospheres of the Earth and planets, and disruption instabilities in tokamaks are related to the development of current sheets in magnetized plasma [1–7]. The dynamics of current sheets and the processes of magnetic reconnection have been actively studied during past decades, in particular, by methods of experimental physics [8–22]. The significance of such investigations is determined not only by the fundamental character of the problems related to magnetic energy transformation in plasma in complex nonuniform magnetic fields but also by the possibility of studying and laboratory modeling of various unsteady astrophysical phenomena based on the current sheet dynamics and magnetic reconnection processes. Results of laboratory experiments can favor better understanding of the nature of phenomena that have a significant effect on the state of the interplanetary space, the Earth’s and planets' atmosphere, and, eventually, the cosmic weather. As is well known, the most powerful manifestations of solar activity are solar flares [1, 3–5] and coronal mass ejections (CMEs) (see [23, 24] and references therein). Both flares and CMEs are generated in active solar regions with a complicated magnetic structure and strong magnetic field. The sources of energy
released during the evolution of CMEs and in flares are nonpotential magnetic fields created in solar active regions by the electric currents flowing in the solar corona. CMEs are often accompanied by the formation of current sheets in which both charged particles and plasma flows are accelerated due to the processes of magnetic reco
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