# Vacuum Electromagnetic Pulse (emPulseInVacuumT.pre)

Keywords:

electromagnetics, laser, plane wave pulse, field energy monitoring

## Problem description

A linearly-polarized (with electric field in the z-direction) electromagnetic pulse with a sinusoidal amplitude on a plane wave is launched from the left side (x=0). The transverse (y, z) boundary conditions are periodic, but the pulse has finite transverse extent.

This simulation can be performed with a VSimBase license.

## Opening the Simulation

The Vacuum Electromagnetic Pulse example is accessed from within VSimComposer by the following actions:

• In the resulting Examples window expand the VSim for Basic Physics option.
• Expand the Basic Examples (text-based setup) option.
• Select Vacuum Electromagnetic Pulse (text-based setup) 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 basic variables of this problem should now be alterable via the text boxes in the left pane of the Setup Window as shown in Fig. 154.

Fig. 154 The Setup Window for the electromagnetic pulse.

## Input File Features

The input file sets the wavelength to be one-eighth of the box length. It computes the CFL stability limit for the time step and sets the actual time step to TIMESTEP_FACTOR times the stability limit for the time step.

One can change the pulse width and length to see more or less diffraction or dispersion.

## 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. You will see the output of the run in the right pane. The run has completed when you see the output, “Engine completed successfully.”

The Run Window, showing settable parameters with the engine output in the right pane, is shown in

Fig. 155 The Run Window for the electromagnetic pulse.

## 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.

The electric and magnetic field components can be found in the scalar data variables of the data overview tab.

• Make sure the Data View drop down is set to Data Overview.
• Here you can see Variables. Expand the Scalar Data.
• Expand B
• Select B_x
• Check the box next to Display Contours and set the # of contours to 10
• Click and drag with your mouse to rotate the view

Initially, no field will be seen, as one is looking at Dump 0, the initial dump, when no fields are yet in the simulation. Move the slider at the bottom of the right pane to see the magnetic field at different times.

Fig. 156 Bx fields at Dump 10.

## Further Experiments

Increase CFL_FACTOR to greater than one. One should then see the simulation go numerically unstable, as one will have violated the CFL condition.

Increase NX to better resolve the wave and see whether it slips less with respect to the box.

Increase the pulse and box widths (you will also need to increase the number of cells in the transverse directions) to reduce diffraction.

Modify the boundary conditions to be a Matched Absorbing Layer (MAL) or Perfectly Matched Layer (PML) to see how the wave is absorbed when it reaches the end of the simulation.