Influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current an
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MA DIAGNOSTICS
Influence of the Initial Parameters of the Magnetic Field and Plasma on the Spatial Structure of the Electric Current and Electron Density in Current Sheets Formed in Helium G. V. Ostrovskayaa, V. S. Markovb, and A. G. Frankb a Ioffe
Physical Technical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia b Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia e-mail: [email protected], [email protected] Received June 17, 2015
Abstract—The influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium plasma in 2D and 3D magnetic configurations with X-type singular lines is studied by the methods of holographic interferometry and magnetic measurements. Significant differences in the structures of plasma and current sheets formed at close parameters of the initial plasma and similar configurations of the initial magnetic fields are revealed. DOI: 10.1134/S1063780X1601013X
ter. It should be noted that formation of such doublehumped plasma sheets was earlier observed in all noble gases [22, 23], but under substantially different initial conditions, namely, in the absence of gas preionization by a θ-discharge, when the initial degree of gas ionization, in contrast to the present work and [9, 24– 26], was lower than 0.2%.
1. INTRODUCTION The possibility of development of current sheets in magnetic fields with X-type singular lines was justified theoretically by S.I. Syrovatskii [1–3]. Study of the evolution of current sheets formed in magnetized plasma is of significant interest for various branches of astrophysics and plasma physics [4–6]. Specially designed laboratory experiments completed with various diagnostics have made it possible to investigate how the initial experimental conditions influence the formation and evolution of current sheets [7–21]. In the present work, we study the influence of the characteristics of the initial magnetic configuration on the spatial structure and dynamics of the electric current and plasma in current sheets formed in helium. The plasma structure was studied by holographic interferometry [9–15], while the distributions of the magnetic field and plasma current were determined from magnetic measurements [16–19]. It was found that, for small gradients h of the transverse magnetic field, plasma sheets had a distinct double-humped structure with two symmetric side maxima of the electron density, whereas for sufficiently large values of h, one-humped sheets with one maximum of the electron density in the central region of the sheet formed. Using magnetic measurements, current structures consisting of two maxima symmetric with respect to the sheet midplane were also revealed during the formation of current sheets in helium. Such structures were observed only at small values of h in the early stage of the sheet evolution; further, they transformed into one-humped shee
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