S. P. Vetchinin

Effect of the rise rate of nanosecond high-voltage pulses on the breakdown of air gaps

The breakdown velocity increases to 10–20 cm/ns when the leading edge of the negative voltage pulse decreases to 0.5–2.5 ns. The sharp increase in the velocity can be explained by the appearance of a short-pulse beam of high-energy electrons which produce in the gap a sufficient number of initial electrons.

Cooperative formation of dust structures in plasma

The formation and destruction of ordered dust structures in glow discharges are investigated experimentally. The initial construction phase of an ordered structure is related to the construction of its cooperative field and is determined by the number of particles and by the existence of crystallization centers. After the structure has been constructed, it influences the local plasma properties and the discharge current-voltage characteristics. The recovery of the structure after weak exposure takes place at local equilibrium, while, after intense exposure to high-voltage nanosecond pulses, it is determined by the fluctuation level and the degree of chaotization in the system.

The Effect of the Gas Temperature Gradient on Dust Structures in a Glow-Discharge Plasma

An experimental investigation is performed of the effect of the neutral gas temperature gradient on plasma-dust formations in the positive column of a glow discharge. It is demonstrated that the thermophoretic forces arising due to the temperature gradient are comparable with radial electric fields and define the condition of formation and different shapes of plasma-dust structures, in particular, the formation of rings in the vicinity of tube walls. A model description of this effect is given.

The action of an electron beam on dust structures in a plasma

The action of an electron beam on ordered dust structures in glow and low-pressure RF discharges was studied experimentally. The electron beam produces destruction and dynamic displacement of the dust structure. In the center of a dust structure, an electron beam with a low electron energy (tens of eV) at currents up to 1 mA caused structural disordering and “melting” in the region of its action but did not excite external crystal regions. Local action of an electron beam with a high electron energy (25 keV) and a beam current above 10 mA caused deformation of the whole dust structure and shifted it in the horizontal direction so that it was carried away from the RF discharge zone. The effect of dust structure displacements can be used to locally remove particles from a plasma.

Ordered structures of microparticles in a glow discharge

The possibilities are analyzed and experimentally investigated of the formation and destruction of structures of charged microparticles in a glow discharge plasma in different gases. The use of a conical discharge tube and the introduction of an orifice plate into that tube enable one to stabilize the strata and obtain dust formations of different types. Given a fairly high concentration of dust particles in a structure, this structure itself affects the local properties of the plasma.

Effect of high-voltage nanosecond pulses on complex plasmas

Influence of high-voltage (1–11 kV) pulses of nanosecond (20 ns) duration on microparticles levitating in a rf plasma is studied. It is shown that the pulses produce significant influence on the plasma, causing perturbations with the relaxation time of the order of 10−4 s. This time is sufficient for the microparticle to acquire significant kinetic energy. Application of repetitive pulses leads to the vertical oscillations of the microparticles. Clusters, consisting of small number of microparticles, exhibit parametric instabilities of horizontal modes under the effect of repetitive pulses. It was shown that the parametric instability is caused by the vertical oscillations of the microparticles in the nonuniform environment of the sheath.

Vapor phase deposition of coatings onto dust particles in combined plasma

Nickel coatings on polydisperse microparticles have been deposited from vapor phase in combined RF discharge-electron beam plasma. Features of the behavior of a dusty plasma cloud in the course of evaporation and deposition of coatings are considered.

Electrical breakdown of soil under nonlinear pulsed current spreading

Laboratory investigations on pulsed current spreading from spherical electrodes and evolution of electrical breakdown of silica sand with different water contents under a 15–20 kV voltage pulse were carried out. A sharp nonlinear decrease in the pulsed resistance of soil was observed when the current density exceeded a certain threshold value. Then ionization-overheating instability develops and leads to current contraction and plasma channel formation in the soil. The method for determination of the threshold electric field for ionization is proposed. Electrical discharge in wet sand was found to develop with a significant delay time for long discharge gaps similar to thermal breakdown.

Parametric excitation and stabilization of dust structures in glow discharge under the action of nanosecond electric pulses

The phenomena of (i) parametric excitation of the resonance oscillations of dust particles due to pulsed heating of plasma electrons in a glow discharge, (ii) spatial stabilization of these particles due to additional local ionization, and (iii) disordering of the dust structure as a result of the breakage of a plasma trap (caused by an increase in the residual ionization in discharge with increasing frequency of the external action) have been experimentally studied.

Dust particles in a thermophoretic trap in a plasma

The feasibility of confining dust particles in a plasma by thermophoretic forces was demonstrated. An extended dust structure in a positive glow discharge column was experimentally obtained at liquid nitrogen temperature. The dust structure was confined in an electrostatic-thermal trap, in which vertical stability was provided by the summed action of longitudinal electrostatic field and thermophoretic forces. Traps of this kind can be analyzed in terms of the general principles developed for confining particles in traps with the use of electric and magnetic multipole fields. We were able to change the shape and volume of the structure and even separate it into parts by varying temperature fields.