Biomedical subjects

Sh Amiranashvili

Publications and source records attributed to Sh Amiranashvili.

6 recordsLinked to original sources

PubMed2006

Measurement and 3D simulation of self-organized filaments in a barrier discharge.

We report on pattern formation phenomena in the filamentary dielectric barrier discharge between plane glass electrodes. It is for the first time that a three-dimensional (3D) self-organized glow pattern was both observed in an actual experiment and directly calculated in a full 3D discharge simulation in a quantitative manner. Specifically, we investigate the genesis of periodic patterns during the first breakdowns. Despite our simple drift-diffusion discharge model, the correspondence of experimental and numerical findings is surprisingly good.

Electrodes↗

PubMed2005

Ionization fronts in planar dc discharge systems with high-ohmic electrode.

Electric breakdown and ionization fronts are considered theoretically in a sandwich-like dc discharge system consisting of two plane-parallel electrodes and a gaseous gap in between. The key system feature is a high-ohmic cathode opposite to an ordinary metal anode. Such systems have received much attention from experimental studies because they naturally support current patterns. Using adiabatic description of electrons and two-scale expansion we demonstrate that in the low-current Townsend mode the discharge is governed by a two-component reaction-diffusion system. The latter provides quantitative system description on the macroscopic time scale (i.e., much larger than the ion travel time). The breakdown appears as an instability of the uniform overvoltage state. A seed current fluctuation triggers a shock-like ionization front that propagates along the discharge plane with constant speed (typically approximately 10(4) cm/s). Depending on the cathode resistivity the front exhibits either monotonic or oscillatory behavior in space. Other breakdown features, such as damping transient oscillations of the global current, can also be found as solutions of the reaction-diffusion equations.

Journal Article↗

PubMed2004

Role of surface charges in dc gas-discharge systems with high-ohmic electrodes.

Surface charge of the electrodes is investigated for planar dc gas-discharge systems. Both analytical estimates and experimental data show that such a charge plays an important role for the dc systems with a high-ohmic electrode. This is demonstrated by several experiments concerning discharge establishment and pattern formation phenomena. The surface charge has an inhibitory role, as it diminishes the electric field in the gas. Due to the low mobility of the surface charges, their distribution can be nonuniform giving rise to the observable filamentary structure of the discharge. It is also shown that the surface charge effect can be naturally incorporated in existing phenomenological models of the planar discharge. Thereby one can explain several observable phenomena, such as stability, multiplicity, and motion of the localized structures.

Journal Article↗

PubMed2003

Nonuniform non-neutral plasma in a trap.

An analytical model for breathing oscillations in a nonuniform non-neutral plasma slab is developed. The plasma is relatively small and warm with the smallest dimension only of several Debye lengths. Nonuniformity in the equilibrium results in a frequency shift associated with pressure and boundary effects. The plasma size and temperature, being related to the frequency shift, can therefore be evaluated from frequency measurements. In particular, for small nonuniform plasmas the frequency of the breathing mode is twice that predicted by the cold fluid theory. Nonlinear oscillations are also considered and the pressure is shown to have an important effect on the dynamics. Analytical solutions for linear and nonlinear oscillations are obtained and compared with that from one-dimensional particle-in-cell simulations. Good agreement is found.

Journal Article↗

PubMed2002

Nonlinear standing waves in bounded plasmas.

An analytical model for nonlinear volume oscillations in a bounded cold plasma is developed. Although here the familiar propagating wave solutions do not exist, exact nonlinear standing waves subject to appropriate boundary conditions can nevertheless be found. The behaviors of the electrons and ions are described self-consistently in terms of Lagrangian variables. The analytical solutions are compared with that from particle-in-cell simulations. Good agreement is found in the regimes of interest.

Journal Article↗

PubMed2002

Non-neutral plasma column in an asymmetric trapping field.

A non-neutral plasma column in an asymmetric trapping field is considered in this paper. It is shown that nonlinearly interacting bulk plasma oscillations and quadrupole surface waves allow an exact analytical description. The absence of symmetry leads to nonintegrability and other nonlinear phenomena, such as passage through different resonances and phase locking. These phenomena should be observable in experiments involving elliptical traps and rotating walls and can affect the latters' applications.

Journal Article↗