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

M Jimenez-Diaz (1) , J van Dijk (1) , J J a M van Der Mullen (1)

1 Department of Applied Physics [Eindhoven]

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.

Mots clés: Physical Sciences

M Jimenez-Diaz, J van Dijk, J J a M van Der Mullen. Effect of remote field electromagnetic boundary conditions on microwave-induced plasma torches. Journal of Physics D: Applied Physics, 2011, 44 (16), pp.165203. ⟨10.1088/0022-3727/44/16/165203⟩. ⟨hal-00613269⟩