Multipacting in Stripline (striplineMultipacting.sdf)



Problem description

This VSimMD example launches a wave into a stripline multipacting geometry and demonstrates multipacting effects.

This example is run in a portion of a TEM transmission line CAD file, and demonstrates how multipacting occurs at specific drive voltages. This is done with the use of a Field Scaling Electron particle species.

This simulation can be performed with a VSimMD license.

Opening the Simulation

The Stripline example is accessed from within VSimComposer by the following actions:

  • Select the New From Example… menu item in the File menu.
  • In the resulting Examples window expand the VSim for Microwave Devices option.
  • Expand the Multipacting option.
  • Select “3D Stripline Multipacting” and press the Choose button.
  • In the resulting dialog, create a New Folder if desired, and press the Save button to create a copy of this example.

The Setup Window is now shown with all the implemented physics and geometries, if applicable. See Fig. 413. As shown in the image, Field Scaling Electrons are being used to be able to simulate multiple field powers in one simulation.

image 1

Fig. 413 Setup Window for the Stripline example.

Running the simulation

After performing the above actions, continue as follows:

  • Proceed to the Run Window by pressing the Run button in the left column of buttons.
  • To run the file, click on the Run button in the upper left corner of the Logs and Output Files pane on the right. You will see the output of the run in the right pane. The run has completed when you see the output, “Engine completed successfully.” This is shown in Fig. 414 below.
image 1

Fig. 414 The Run Window at the end of execution.

Visualizing the results

After performing the above actions, continue as follows:

  • Proceed to the Visualize Window by pressing the Visualize button in the left column of buttons.

To view the exponential increase in electrons as in Fig. 415:

  • Select History under the Data View drop down
  • Set Graph 2 to numRealElectrons
  • Set Graphs 3 & 4 to None
image 1

Fig. 415 The numRealElectrons history shows exponential growth in the number of electrons.

To view the voltage at which multipacting occurs in the stripline, as seen in Fig. 416:

  • Select Phase Space under the Data View drop down
  • Set the X-axis to electrons_fieldScaleParameter
  • Set the Y-axis to electrons_weight
  • Set the Color to electrons_weight
  • Press Draw.
  • Move the slide to the right to see how the multipacting growth is occurring.
image 1

Fig. 416 The multipacting occurs at a scaling value of around 2.5. You can use this to multiply the value of START_VOLTAGE to find out the voltage at which multipacting occurs. In this case that is around 60.0 Volts

Further Experiments

Try varying the parameter VOLTAGE to observe when multipacting occurs. For example, multipacting does not occur for VOLTAGE = 45.0 Volts.