In CST Wake Field Solver, you can define an arbitrary beam profile by using the "Import Beam" feature. This allows you to import a custom beam distribution from an external file or by specifying the data points directly within the software. Here's a general overview of the process:

Launch CST Wake Field Solver and open your project or create a new one.

Set up the geometry and other parameters of your simulation, including the accelerator structure, wake field monitors, and any other necessary components.

In the "Wake Field Solver" module, locate the "Beam" section or tab, which is typically where you define the properties of the particle beam.

Look for the "Import Beam" option or a similar feature that allows you to define a custom beam profile.

If you have a pre-existing file that contains the desired beam profile, click on the "Import Beam" button and select the appropriate file format. CST Wake Field Solver supports various file formats for importing beam profiles, such as ASCII, CSV, or specific accelerator formats like Elegant or Track.

If you don't have a file but want to specify the beam profile directly within CST Wake Field Solver, check if there is an option to enter the data points manually. You can define the position, momentum, charge, and other parameters for each data point in the beam profile.

Depending on the specifics of your simulation, you may also need to provide additional information such as the beam energy, bunch length, particle species, or other beam properties. Refer to the documentation or user guide of CST Wake Field Solver for the exact parameters and their respective definitions.

Once you have imported or defined the arbitrary beam profile, make sure to verify and adjust any other simulation parameters as necessary.

Run the simulation to compute the wake fields and observe the beam behavior based on the defined profile