Ion Temperature Distribution in Current Sheets Formed in Argon Plasma
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MA DYNAMICS
Ion Temperature Distribution in Current Sheets Formed in Argon Plasma N. P. Kyriea,*, A. G. Franka, and D. G. Vasilkova, b a Prokhorov
General Physics Institute of the Russian Academy of Sciences, Moscow, 119991 Russia b Bauman Moscow State Technical University, Moscow, 107005 Russia *e-mail: [email protected]
Received October 12, 2018; revised October 25, 2018; accepted October 25, 2018
Abstract—The processes of heating and acceleration of argon ions in different charge states in current sheets formed in 2D and 3D magnetic configurations were studied experimentally. It is shown that the temperature of argon ions depends on the ion charge state. The maximum temperatures of Ar II, Ar III, and Ar IV ions are found to be 60, 120, and 200 eV, respectively. The time of energy exchange between ions due to Coulomb collisions is much shorter than the current sheet lifetime, which indicates that ions in different charge states reside in different sheet regions located at different distances from the sheet midplane (y = 0). It is shown that Ar II and Ar III ions are accelerated to energies of W xmax ≈ 200 eV. It is found that the temperature and the energy of directed motion of Ar II, Ar III, and Ar IV ions do not depend on the magnitude of the longitudinal magnetic field. Argon ions Ar IV radiating in the near UV region are detected for the first time in the current sheet plasma. DOI: 10.1134/S1063780X19040032
1. INTRODUCTION During past several decades, studies of current sheets (CSs) and magnetic reconnection processes occurring in them have been aimed, first of all, to reveal the nature of flare phenomena in magnetized plasmas, such as flares on the Sun and stars, substorms in the magnetospheres of the Earth and planets, disruption instabilities in tokamaks, etc. [1–9]. Along with astrophysical observations and theoretical studies, special experiments were carried out to clarify specific features of CSs formed under different conditions (see [9–14] and references therein). Moreover, in spite of very different spatial scales and different values of the plasma parameters, magnetic fields, and currents, a striking similarity has been observed between laboratory CSs and the CSs formed in the Earth’s magnetosphere [14–18], which indicates a common nature of the fundamental processes occurring in laboratory and space plasmas. Many plasma processes in laboratory CSs were investigated using plasma spectroscopy—a contactless diagnostics, which introduces no perturbations in the object under study [19–35]. Using spectral methods, the electron temperature [21, 24, 25], the temperature and energy of accelerated ions [24–33], the plasma density in different CS regions [19, 20, 22, 25, 26, 28– 31], and the strengths of anomalous electric fields [23] (see also [25] and the references therein) were determined.
One of the most interesting effects detected by spectral methods was a sharp increase in both the electron and ion temperatures immediately before the end of the CS metastable phase and the transition into the pulse
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