L. M. Vasilyak

Coulomb stable structures of charged dust particles in a dynamical trap at atmospheric pressure in air

A mathematical simulation of a dust particles behavior in the electrodynamic linear quadrupole trap with closing end electrodes allowed us to reveal several features of the phenomena. Regions of stable confinement of a single particle, in dependence of frequency and charge-to-mass ratio, were determined. With an increase of the mediums dynamical viscosity, the region for confining charged particles by the trap becomes wider. We obtained values of the maximum quantities of charged particles confined by the trap at atmospheric pressure in air. Firstly, we presented observations of ordered Coulomb structures of charged dust particles obtained in the quadrupole trap in air at atmospheric pressure. The structures consisted of positively charged oxide aluminum particles 10?15??m in size and hollow glass microspheres 30?50??m in diameter. The ordered structure could contain particles of different sizes and charges. The trap could confine a limited number of charged particles. The ordered structures of charged micro-particles obtained in the experiments can be used to study Coulomb systems without neutralizing the plasma background and action of ion and electron flows, which are always present in non-homogeneous plasma.

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.

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.

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.

Investigation of Electric Discharges in the Vicinity of a Charged Aerosol Cloud and Their Interaction with a Laser-Induced Spark

It is experimentally demonstrated that an extended laser-induced spark developed in the vicinity of a grounded electrode and having a structure in the form of separate spherical plasma formations may intercept the channel of a leader discharge developing from the grounded electrode to an artificially charged aerosol cloud. The interception occurs with the electric field intensity in the vicinity of the electrode being close to the value required for an upward positive leader. It is registered that the presence of a laser-induced spark in the vicinity of the electrode causes a manifold reduction of the time of stable leader formation. It is found that the emergence of an extended laser-induced spark of a CO2 laser in the vicinity of the boundaries of a highly charged aerosol cloud does not provoke a discharge to ground from the cloud.

Temperature effect on the burning time of a low-pressure discharge in a quartz discharge tube with a protective layer

It is shown that an increase in the temperature of a quartz discharge tube with a protective layer of rare earth metal oxides on the inner surface leads to a decrease in the burning time of a low-pressure arc discharge in inert gases. In this case, the dominant mechanism that leads to a decrease in the burning time is the loss of electron emission because of the complete sputtering of the emitting material of the oxide electrodes.

Protective coatings with a mixed composition for low-pressure discharge amalgam lamps

The decrease of the ultraviolet radiation of high-power low-pressure discharge amalgam lamps with a protective coating with a mixed composition based on spinels and oxides has been experimentally studied. It has been shown that these coatings exhibit fairly high protective properties at low pressures of the buffer gas mixture and provide useful lifetime of the lamps comparable to that of the best oxide coatings.

Influence of a low frequency electric field on dusty structures under microgravity conditions

The experiments performed onboard the International Space Station (ISS) demonstrate that a formation of homogeneous 3D dusty plasma structures under microgravity conditions is accompanied by the same difficulties as in laboratory. The plasma flows connected with plasma nonuniformity and a leaving of charged particles on walls lead to an appearance in the discharge center of a region free of dust grains, the so-called void. We present the analysis of the experiments performed onboard the ISS with the PKE-Nefedov facility when an additional low frequency (lf) voltage was applied to the electrodes. The sketch of the RF plasma chamber with the rf parallel plate discharge is well known. The aim of these experiments was an increase of a stability of dust structures and a void closure under an action of an external electric field. When the rf voltage amplitude increases the void axial size decreases and the radial size, on the contrary, increases. The void is being closed practically without a distortion of its form when the rf voltage on the electrodes decreases. The void boundary is sharp at all pressures analysed. When we apply the additional If voltage the void behavior is quite different a new additional force acting on the dust particle in the electrostatic trap generated by the averaged rf plasma fields modulated by the low frequency voltage appears. This force, as applied to the dust particles, was not considered previously. The force can be called as the force of the dynamical low frequency pressure by analogy with the force of the high frequency pressure which confines, for example, ions in the radio frequency Paul trap. This force appears due to the low frequency modulation of the grain equilibrium position in the nonuniform electric field of the trap. The amplitude of dust grains oscillations in the low frequency field does not exceed the interparticle distance and is about 200 microns. The dust grains are shifted under the action of this force in the direction of the weaker electric field that is to the trap center. When the amplitude of the low frequency modulation is comparable with the rf voltage amplitude on the electrodes, this force is comparable with the electric field force. This will serve to the void closure when the low frequency voltage is applied to the discharge. When the low frequency field is imposed on the rf discharge initially grains are shifted to the center from the regions with higher electric field. Consequently, the void starts to close from its boundary.