Effect of remote field electromagnetic boundary conditions on microwave-induced plasma torches

Abstract

Abstract.A flexible versatile electromagnetic model constructed with the PLASIMO platform is employed to explore electromagnetic features of microwave induced plasma torches. The bases, formed by a full-vector formulation of the Maxwell equations, provides the possibility to formulate the boundary conditions in a natural way. Together with the use of a direct matrix solver this gives a convergence speed-up of more than a factor of 100 when compared to a scalar formulation on the azimuthal magnetic field that uses an iterative solver. As a result this electromagnetic model is ready to act in future studies as part of the self-consistent description of plasma-electromagnetic coupling. With the electromagnetic model three types of configuration were studied: the closed, semi-open and open configurations, all three based on the same simplified model-plasmas. It is found that the closed configuration, acting as a cavity for which the (de)tuning is extremely sensitive for the plasma conditions, is less suitable for applications in which changes in plasma compositions can be expected. The semi-open configuration can be seen as a model for the practice often used in laboratories to place Microwave Induced Plasma torches in a grid that aims to protect the environment against microwave electromagnetic radiation. Calculations show that this is good practice provided the radius of this cylindrical grid is in the order of 90 mm. For the most often used configuration, the open version, we found that the power balance as expressed by the coefficients of absorption, transmission and reflection, depends on the electron density of the plasma. The reason is that the plasma acts as an antenna, that converts the electromagnetic waves from the co-axial structure to that of the expansion region and that this antenna function depends on the electron density. The influence of various other antenna elements is investigated as well.

Study of Gas Heating by a Microwave Plasma Torch

“…As mentioned in Section 3, the calculations were made imposing the plasma conditions (values and profiles for the electron density and temperature), which are given in the appendix. These conditions agree with our experimental observations and are also supported by other works [9,11,21]. The plasma impedance changes with n e and ν (see Equation (2)) [22], thus affecting the wave-plasma power coupling.…”

“…The electron density is deduced from Stark broadening measurements of the H β line [19,20], recorded using a [8][9][10][11][12][13][14][15]. The electron temperature could not be measured due to the experimental lack of precision.…”

“…Since the 80s, the TIA has been studied by different research groups (from the University of Montreal, the Technical University of Eindhoven and the University of Cordoba) that focus mainly on the experimental characterization of the plasma it creates [7,9,10], paying also some attention to its electromagnetic and hydrodynamic modeling [11,12]. These studies have shown that the TIA could be efficient in applications such as analytical chemistry [13] (in relation also with its ability to create chemically active species), surface treatment [14] and gas treatment [15].…”

Plasma pencil as an excitation source for atomic emission spectrometry

“…2 As a minority, some alternatives, e.g. capacitively coupled plasma (CCP) [4][5][6][7] or microwave-induced plasmas (MIPs) 8 are studied for analytical purposes and various sub-types were constructed. The sensitivity of discharges to water presence is a substantial limitation and can be eliminated in some cases by hydride generation, 3,9 for example, or a special desiccation system must be employed.…”

Numerical and experimental analysis of radiation from a microwave plasma source of the TIAGO type

“…Usually discharge shielding is assumed in numerical calculations [10][11][12][13][14] and, even if not, as in [15], omitting the shielding does not affect the results (since a waveguide below the cut-off frequency is used). To our knowledge, the first article that deals with this issue is [16], where the authors determine the influence of the remote boundary conditions (BCs) on the ratio of the radiated power to the power delivered to the plasma in a frequently used MPS, called TIA (from the French 'Torch Injections Axiale') and disclosed in [17]. The analysis is performed numerically by assuming the axial symmetry of the device and a cylindrical shape of the computation domain.…”