Plasma Applicator - CST2013 MWS Examples

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General Description

This simple microwave plasma applicator example shows how materials with dielectric dispersion of 2nd order can be taken into consideration. The behavior of a cold plasma with losses created by particle collisions can be described by the Drude model. Determining factors are the plasma frequency (which is directly related to the electron density of the plasma) and the collision frequency, which describes the probability of collisions between electrons and neutral atoms or molecules.

The applicator contains a quartz tube which is evacuated. The incoming microwave can ignite a plasma. Inside the quartz tube different plasma densities dependent on the radius are given. The values can be extracted from measurements or calculated by using Bessel functions, which could be done by making use of a VBA macro.

Structure Generation

The main settings for the plasma applicator can be done using the waveguide template, defining the PEC boundary and background material as well as the units settings. Due to the symmetry of the structure one magnetic symmetry plane is activated to save simulation time.

The model is constructed by defining a brick as the coupling waveguide and a cylinder representing the quartz tube. Using the shell facility the several plasma layers are realized.

Solver Setup

At one end of the given coupling waveguide a waveguide port is defined to excite the plasma applicator. The excitation signal is a Gaussian shaped pulse referring to the frequency range from 1.9 to 4.1 GHz.

In order to analyze the field distribution inside the different plasma layers several electric 3D field monitors are defined at different frequency points.

Post Processing

The monitored 3D fields are listed in the navigation tree in the folder 2D/3D Results. Regarding the fields inside the tube represents the plasma effects at different frequency points. It can be seen how some layers of the plasma get 'overcritical', that means the plasma frequency is higher than the operation frequency and the electromagnetic wave cannot penetrate the plasma layer anymore or is strongly damped inside.

In addition the time signals and the corresponding scattering parameters of the transient calculation can be found in the folder 1D Results.