Rotational motion of dusty structures in glow discharge in longitudinal magnetic field

Abstract

The investigation of dust structure formed in glow discharge in an external longitudinal magnetic field with induction up to 400 G applied is presented in this work. The dust structure starts to rotate in the magnetic field. The angular-velocity magnitude is one to two orders larger than one in other discharge types. Its dependence on the magnetic field is nonmonotonic. The rotation direction inverses with an increase of the magnetic induction value up to a certain magnitude B0. In close range of induction around B0 and under certain conditions the rotation of the upper and lower parts of the structure in the opposite direction is observed. Rotation is caused by the ion-drag force. The inversion of rotation direction relates with the change of plasma flows in the area of their formation in stratum with the magnetic field applied. The effect of ion flows was investigated in two additional experiments on the observation of structure rotation onset and on gravity-driven probing of stratum. The angular-velocity unhomogeniety allowed us to investigate shearing and to observe melting of the dust crystal. The correlation functions approach showed the occurrence of structure transformation and its phase transition of the meltinglike type in the magnetic field.

Streaming Complex Plasmas: Ion Susceptibility for a Partially Ionized Plasma in Parallel Electric and Magnetic Fields

“…By adjusting the magnetic field strength it is possible to create plasma states where only the electrons, electrons and ions, or possibly all three charged particle species including the dust particles are magnetized [4]. Several new phenomena have been observed in experiments with magnetic fields, including a slow rotation of the entire dust cloud [5][6][7][8][9], the spinning of dust particles [10], and complicated flow patterns [11]. In recent experiments with strong magnetic fields on the order of a few Tesla, sufficient to magnetize not only the electrons but the ions as well, filaments appeared in the discharge [12].…”

Detection of eddy current in the striation

“…- Figure 2 represents the results of probing of the hole investigated area of the discharge in the form of dependence of the angular velocity of particles with size 4.1 µm on the vertical coordinate which counted from the shining border of striations to the anode side. It is visible in the schedule that in the center of the striation (in the area where particles levitate in [7], h = 0-5 mm) the projection of the angular velocity of the probing particles to the direction of the magnetic field has negative sign. In the areas under and over the striation, the projection of the angular velocity has positive sign.…”

“…-The search of eddy current was carried out in the area of the discharge where the first striation and the lower part of the second ones were situated. The stratified positive column of the DC discharge was placed in the vertical magnetic coils, the experimental setup was the same as in [7]. The probing was done by dust particles falling through the discharge.…”

“…One of the productive methods of studying a complex plasma consists in imposing an external influence and an observation of the response of the system. Imposing a magnetic field on low-temperature plasma with the dusty component has revealed new mechanical and thermodynamic properties, namely, change of the order of the system and kinetic temperature of the particles, of viscosity [5][6][7][8], as well as the magnetic properties because the dusty component possesses paramagnetism [9][10][11]. Probably the most interesting feature of dusty plasma in magnetic field is the complex dynamics of the rotational motion which shows an inversion of the direction angular velocity of the rotation of dust structure.…”

“…The sharp standing striations existed under these parameters and the azimuthal movement of particles was observed during the necessary number of video frames. We have chosen the value of the magnetic field in which the competing processes defining rotation according to [7,8] could work.…”