Helena Nowakowska

Propagation characteristics of surface waves sustaining atmospheric pressure discharges : the influence of the discharge processes

The propagation characteristics of microwave frequency surface waves along atmospheric pressure plasma columns sustained in capillary tubes by these same waves are studied analytically and numerically. In contrast to what has been done to date in such a pressure range, our analysis includes the modelling of the discharge processes in order to account for their interdependence with the waves propagation. To describe these processes and to determine the plasma parameters, we turn to a two-temperature model for non-equilibrium plasmas. The analysis of the wave dispersion is performed using a cold plasma, linear dielectric description; it assumes the local uniformity approximation, which is scrutinized. Also, we assume that the phase and attenuation coefficients of the wave, under given discharge conditions, depend only on the amount of power dissipated in the plasma per unit length. The obtained results are compared with known experimental data.

Designing an efficient microwave-plasma source, independent of operating conditions, at atmospheric pressure

The surfaguide is a waveguide-based electromagnetic-surface-wave launcher that allows sustaining long plasma columns using microwaves. Its electrodynamic characteristics are examined experimentally and theoretically in the perspective of achieving an efficient plasma source without any need for impedance matching retuning as operating conditions are varied over a broad range. The plasma source design and its modelling using equivalent-circuit theory are described and a simple procedure is provided to determine the optimum dimensions of the surfaguide that maximize the transfer of microwave power to plasma. As an example, with an optimized surfaguide, the reflected power in an N2 discharge at atmospheric pressure stays below 3% for powers in the 2?6?kW range and gas flow rates in the 30?150?l?min?1 domain under varying concentrations (< 2%) of admixed gases such as SF6, O2 and argon.

Propagation characteristics of electromagnetic waves along a dense plasma filament

The characteristics of electromagnetic waves propagating along dense plasma filaments, as encountered in atmospheric pressure discharges, are examined in the microwave frequency range; they turn out to be surface waves. Results of numerical calculations of the dependence of the phase and attenuation coefficients on the plasma parameters are presented. In the limit of large electron densities, this guided wave is akin to a Sommerfeld wave and the propagation can be described in an analytical form.

Production of hydrogen via conversion of hydrocarbons using a microwave plasma

In this paper, results of hydrogen production from hydrocarbons in the atmospheric pressure microwave plasma are presented. As sources of hydrogen, both methane CH 4 and tetrafluoroethane C 2 H 2 F 4 were tested. A new waveguide-based nozzleless cylindertype microwave plasma source was used to convert hydrocarbons into hydrogen. The processed gaseous hydrocarbons were introduced to the plasma by four gas ducts which 2 formed a swirl flow in the plasma reactor. The absorbed microwave power was up to 5 kW. The gas flow rate was up to 212 l min -1. The hydrogen mass yield rate and the corresponding energetic hydrogen mass yield were up to 866 g[H 2 ] h -1 and 577 g [ H 2 ] per kWh of microwave energy absorbed by the plasma, respectively. These parameters are better than our previous results when nitrogen was used as a swirl gas and much better than those typical for other plasma methods of hydrogen production (electron beam, gliding arc, plasmatron).

Numerical Analysis and Optimization of Power Coupling Efficiency in Waveguide-Based Microwave Plasma Source

Three-dimensional electric field distributions in a waveguide-based microwave plasma source (MPS) have been determined numerically. Tuning characteristics of the MPS have been calculated using a direct and newly proposed two-port network method. A method for easy assessment of the quality of a set of the tuning characteristics is presented. Optimization of the plasma source has been performed using these characteristics to ensure good power coupling and stability of the plasma source operation. The calculated tuning characteristics have been compared with experimental ones. Good agreement has been found.

Modelling of atmospheric pressure, RF and microwave discharges sustained by travelling waves

A channel-type model for RF and microwave discharges, operating under a local thermodynamic equilibrium (LTE) regime and sustained by travelling waves, is proposed. Such discharges are, as a rule, axially non-uniform. The channel model presented includes this feature. From the analysis that follows, two functions of the value of the heat flux potential at the axis (SA) turn out to be necessary to determine the spatial structure of the discharge. These are L(SA), the power dissipated per unit length of the plasma column, and alpha (SA), the wave attenuation coefficient. From these, the spatial distribution S(r,z) of the heat flux potential can be obtained. Under LTE conditions, this is sufficient to determine the distributions of all plasma parameters of interest. As an example, the spatial structure of a nitrogen discharge sustained by a surface wave is calculated.

Numerical Analysis of Tuning Procedure of a Waveguide-Based Microwave Plasma Source

Numerically obtained electric field module distributions inside a waveguide-based high-flow microwave plasma source (MPS) with a plasma column inside during a tuning procedure that employs a microwave plunger are presented. Standing-wave patterns have been obtained for each plunger position. The optimal position of the plunger has been found. Strong skin effect is seen in the plasma generated in the presented MPS.

Experimental Investigation Of Atmospheric Pressure Surface Wave Discharges

Microwave atmospheric pressure discharge in neon sustained by surface waves in a dielectric tube is considered. The plasma column length was measured versus absorbed microwave power for different discharge conditions. This gives a view on the wave propagation characteristics. The predicted dependence of discharge length on the total flux of wave power based on the modified model of non‐equilibrium plasma is compared with experimental values. Moreover, we present results of spectroscopic investigations of the electron density. The electron density was determined using the method based on the Stark broadening of Hβ spectral line. The spectroscopic results we shall use developing of a model of propagation of surface wave.