Self-consistent axial modeling of surface-wave-produced discharges at low and intermediate pressures

Characteristics of 2.45 GHz Surface-Wave-Sustained Argon Discharge for Bio-Medical Applications

Cold atmospheric plasma (CAP) applications in various fields, such as biology, medicine and agriculture, have significantly grown during recent years. Many new types of plasma sources operating at atmospheric pressure in open air were developed. In order to use such plasmas for the treatment of biological systems, plasma properties should fulfil strong requirements. One of the most important is the prevention from heating damage. That is why in many cases, the post-discharge region is used for treatment, but the short living particles in the active discharge zone and reactions with them are missed in that case. We use the active region of surface-wave-sustained argon plasma for biological systems treatment. The previous investigations showed good bactericidal, virucidal, seeds germination and decontamination effects at a short treatment time, but the discharge conditions for bio-medical applications need specific adjustment. A detailed theoretical and experimental investigation of the plasma characteristics and their possible optimization in order to meet the requirements for bio-medical applications are presented in this paper. The length of the plasma torch, the temperature at the treatment sample position and the microwave radiation there are estimated and optimized by the appropriate choice of discharge tube size, argon flow rate and microwave power.

Modeling of surface-wave discharges with cylindrical symmetry

This paper presents the modeling of microwave (2.45GHz) discharges with cylindrical symmetry, produced in the absence of an external magnetic field by TM00 surface waves (SW) within either cylindrical or coaxial structures. A stationary, one-dimensional (radial) moment model (including the continuity and the momentum-transfer equations for electrons and positive ions, and the electron mean energy transport equations) is solved self-consistently coupled to Poisson's equation for the space-charge electrostatic field and the appropriated Maxwell's equations for the SW electromagnetic field. The model is solved for argon discharges over a broad range of operating conditions: Average electron densities from 10;{11}to3x10;{12}cm;{-3} and gas pressures from 10;{-2}to5Torr . Results are compared to those of a simplified classical model that disregards charge separation near discharge boundaries, ignoring also the development of electron-plasma resonances caused by the severe electron density gradients within space-charge sheath regions. Simulations show that the presence of a sheath-resonance region has a strong influence on the values of the SW attenuation constant, particularly at low pressures and high electron densities, affecting also the local budget of the discharge power deposition (hence discharge maintenance).

Numerical modeling of the electrical breakdown and discharge properties of laser-generated plasma channels

An extensive nonequilibrium steady-state kinetics model incorporating collisional and radiative processes is developed to study the electrical breakdown and discharge maintenance of laser-induced atmospheric plasma channels formed in externally applied electric fields. The model is based upon a self-consistent numerical solution of the Boltzmann equation for the electron energy distribution function coupled with the electron energy balance equation and the population balance equations for electrons and air species. Using the electron energy distribution function, the ionization and electron attachment rates as a function of the reduced applied electric field at different degrees of ionization are calculated. We find that the ionization rate as a function of applied electric field in a laser-induced plasma channel is orders of magnitude larger than that obtained for a natural atmospheric air discharge. Therefore, the electrical breakdown of these plasma channels may occur at significantly lower applied electric fields. The present model predicts a breakdown electric field of 10kVcm , while the experimentally determined breakdown field strength is approximately 5.7kVcm [A. P. Baronavski, NRL Memorandum Report No. NRL/MR/6110-02-8642, 2002 (unpublished)], a reduction of about a factor of 5 from the natural Paschen electrical breakdown field of approximately 30kVcm .

Parameters and equilibrium profiles for large-area surface-wave sustained plasmas

The equilibrium profiles of the plasma parameters of large-area rf discharges in a finite-length metal-shielded dielectric cylinder are computed using a two-dimensional fluid code. The rf power is coupled to the plasma through edge-localized surface waves traveling in the azimuthal direction along the plasma edge. It is shown that self-consistent accounting for axial plasma diffusion and radial nonuniformity of the electron temperature can explain the frequently reported deviations of experimentally measured radial density profiles from that of the conventional linear diffusion models. The simulation results are in a good agreement with existing experimental data obtained from surface-wave sustained large-diameter plasmas.