S. I. Pavlov

Control of ion drag in a dusty plasma

A method of the control of the ion drag force acting on a dust particle in a complex plasma by choosing the composition of the gas mixture of a discharge has been proposed and experimentally implemented. The addition of a heavier additive with a lower ionization potential to the light buffer gas changes the ion composition and velocity of the ion flow. As a result, the ion drag force changes significantly. The experiments have been performed with the discharge in a helium-xenon mixture in a magnetic field. The measured angular rotation velocity of the dusty structure is in agreement with the numerical estimate of the ion drag force varying (increasing) in the presence of small (<5%) xenon additive. The proposed method can be used to create plasma crystals with new properties.

Detection of eddy current in the striation

The dynamics of the dust structures created in striations in the glow discharge in a magnetic field has a complex character which is shown in the inversion of the direction of the movement. The hypothesis of existence of eddy current in the striation which in the magnetic field causes the rotation of dust structures by means of the Ampere force has been offered and developed in the recent works of Nedospasov et al. and Dyachkov et al. In the present work, the experiment in which eddy current in various phases of striations is registered by means of probing dust particles is carried out. It is shown that for various discharge conditions and various magnetic fields the dragging by the rotating gas and the ion drag are the dominating forces defining the dynamics of dust structures in striations.

An experimental study of the degradation of particles in complex plasma

Changes of melamine–formaldehyde resin (MF-R) particles occurring in complex dusty plasma have been investigated. Using a specially developed method, plasma-modified MF-R particles have been extracted from a dust trap after levitation for various periods of time and studied by electron microscopy techniques. Changes in the surface structure of MF-R particles are determined, and quantitative data on the variation in particle dimensions depending on the time of occurrence in plasma are obtained.

Dynamics of plasma−dust structures formed in a trap created in the narrowing of a current channel in a magnetic field

The geometry and dynamics of plasma−dust structures in a longitudinal magnetic field is studied experimentally. The structures are formed in a glow-discharge trap created in the double electric layer produced as a result of discharge narrowing by means of a dielectric insert introduced in the discharge tube. Studies of structures formed in the new type of glow-discharge trap are of interest from the standpoint of future experiments with complex plasmas in superstrong magnetic fields in which the dust component is magnetized. Different types of dielectric inserts were used: conical and plane ones with symmetric and asymmetric apertures. Conditions for the existence of stable dust structures are determined for dust grains of different density and different dispersity. According to the experimental results, the angular velocity of dust rotation is ≥10 s–1, which is the fastest type of dust motion for all types of discharges in a magnetic field. The rotation is interpreted by analyzing the dynamics of individual dust grains.

On the mechanism of own rotation of dust particles

We analyze the physical reason for own rotation of dust particles. We propose from analysis of literature data and our previous studies that own rotation of dust particles is due to azimuth-symmetric flow of ions to the particle surface, which is associated with a nonuniform distribution of the surface charge. This assumption is in conformity with the results of experiments in which the plasma flow is changed by introducing particles in the horizontal plane (horizontal cluster) and particles aligned along the discharge current (vertical cluster) and with the observation of the rotation threshold for the discharge current and the magnetic field. The experiments are performed with spherical particles using the coordinate tracing method. Our results make it possible to construct a model of spinning of charged dust tops for describing magnetic properties of a complex plasma.

Ion drag as a mechanism of plasma dust structure rotation in a strata in a magnetic field

In experiments on complex plasmas, afixed strata region in which the levitation of dust structures is observed is investigated using the method of probing by calibrated dust particles of different sizes in an applied magnetic field under elevated pressures. The measured azimuthal velocity of the probing particles corresponds to the action of the ion drag force for 4 μm-size particles and to the entrainment by the rotating gas owing to the electron vortex flow inside the strata for 1 μm-size particles. Extrapolation to pressures and magnetic fields in which the rotation inversion of dust structures is observed in experiments shows that the ion drag is the dominating force causing rotation with a negative projection of the angular velocity onto the magnetic induction.