On the Magnetomechanical Effect in a Low-Pressure Steady-State Discharge
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TICAL, NONLINEAR, AND SOFT MATTER PHYSICS
On the Magnetomechanical Effect in a Low-Pressure Steady-State Discharge R. Z. Shaikhitdinova,* and V. M. Shibkovb aBashkir
State University, ul. Frunze 32, Ufa, 450074 Russia State University, Moscow, 119992 Russia *e-mail: [email protected]
bMoscow
Received June 5, 2018
Abstract—A unified mechanism explaining the rotation of a suspension and the azimuthal rotation of a dust structure in the plasma of a vertically oriented gas discharge placed in a longitudinal magnetic field is proposed. Basically, it consists in the action of a magnetic field on the electric current produced by the directed motion of ions in the layer of space charge around the solid bodies placed in a plasma. The derived expressions, which define the dependences of the torque of the magnetomechanical effect acting on the plate and the angular velocity of azimuthal rotation of the dust structure on external plasma parameters, qualitatively correspond to the experimental results. DOI: 10.1134/S1063776118100096
1. INTRODUCTION A torque is known [1–4] to act on light dielectric bodies located in a vertically oriented positive gas-discharge column when a longitudinal magnetic field is applied. This manifests itself in the rotation of a plate suspended along the tube axis [1, 2] and in the angular rotation of micron-sized dust particles placed in a plasma [3, 4]. The authors of [1, 2] called the experimentally observed plate rotation the magnetomechanical effect (MME) and explained it by the gas rotation under the Hall diffusion of charged particles moving in crossed radial electric and axial magnetic fields. However, in a gas-discharge plasma in a tube with nonconductive walls there is no radial electric current and the torque of the Ampere force capable of rotating the gas is zero [5]. Nevertheless, quite a few experimental works aimed at the detection of azimuthal gas rotation are known. For example, the direct detection of neutral gas rotation by a spectroscopic method from the measurement of the Doppler shift in atomic lines when a magnetic field was applied to a positive gasdischarge column was reported in [6]. The measured rotation velocities turned out to be very high, up to 50 m s–1 for helium and 150 m s–1 for krypton. At the same time, the authors point out that the neutral gas rotation is difficult to explain, because the volume magnetic force density is zero in a longitudinally homogeneous plasma in the absence of a radial current component. MME studies and, in particular, experiments aimed at the detection of azimuthal gas rotation were carried out in [7] and several other papers of these
authors. The results of experiments based on a technique similar to that in [2] showed that a suspension placed in a gas discharge is deflected in a magnetic field, revealing a maximum in the dependence on magnetic field strength. No gas rotation was detected at a sensitivity of the setup to determine the linear velocity equal to 15 m s–1. The velocity estimates corresponding to the experimental values of t
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