SPARK3D User Manual

Computing voltage

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With Paraview it is also possible to compute the voltage as the integration of the electrical field between two points in the mesh. In SPARK3D, the fields are defined for an input power of 1W, therefore the computed voltage is also at 1W, called V1W. This can be useful for multipactor to translate from breakdown power to breakdown voltage and compare results with theoretical parallel-plate predictions. The expression to convert from power to voltage is the following:

V=V1W√P

Be careful because the voltage computed this way depends on the selected path in the mesh. In order to have meaningful results, the device geometry and fields, should be similar to a parallel-plate case.

The process is as follows:

- Apply paraview filter "plot over line"
- Specify the coordinates of the line.
- Apply paraview filter "Integrate variables". The line must be entirely contained in the mesh. Otherwise this step will lead to NaN value.

In this particular case we will compute the voltage in the center of the centre iris, where the maximum field is located. In order to do so, one has to select the "**Plot Over Line**" filter in Filters->Alphabetical->Plot Over Line menu.

Select the line for displaying the data by either moving the start and end points with the mouse, or by inserting coordinates manually. In this case, just press "y axis" button to automatically orient the line properly. Adjust the y coordinates between [-0.001085 and 0.001085] to confine the line inside the gap (gap size is of 2.17mm in this example). Then press "Apply" button.

A 2D plot with the fields displayed along the selected line appears. Now, apply another filter called "**Integrate Variables**" in Filters->Alphabetical->Integrate Variables. This filter will integrate all quantities displayed in the 2D plot.

In this case, **we obtain a voltage at 1W of V1W= 18.4 V** as shown below.

**Note:** Line start and end points must be adjusted to be inside a valid data region. If any of the line nodes lies outside, NaN integration values may appear.