Discussion Forum

1. Did you try all of these things to reduce your model size?: "If your MPH-files are large, you can greatly reduce their size by selecting Clear All Built Meshes from the Mesh menu and Clear All Solutions from the Study menu, and then saving your MPH-files. If you are using COMSOL Multiphysics® version 5.2a or later, then go to the File Menu > Preferences, Files section. For the Saving COMSOL application files setting, change the Optimize for setting to File Size. This reduces the saved file sizes for COMSOL® application files."
2. Can you reproduce the identical issue in a simpler model, and then upload that?

Yes, I did all of those things. However, I simplified the model and have uploaded it here.

I managed to fix the boundary selection issue. I realized that I needed to enclose the domain of study within another geometry to provide walls (this is not required in electrostatics due to the boundary element method providing for an infinite void).

I got the study to run, but I still could not select the electric field I computed to provide a force. As such, the trajectories are not influenced at all by the electrodes. This is a major problem. How do I fix it?

You seem to be not properly coupling the multiphysics. You might want to take a look at https://www.comsol.com/model/pierce-electron-gun-87781

I don't want to couple multiphysics. The effect of the particles on the field is negligible. I want to see how they would behave under an already computed electric field.

And even if I wanted to, there is no multiphysics coupling available between Electrostatics, Boundary Elements asnd Charged Particle Tracing!

You don't have to limit your models to Comsol's pre-set multiphysics couplings. You can simply follow one study step with another, using the fields computed from Step 1 (limiting it to electrostatics) to provide field conditions in Step 2 (limiting that step to charged particle tracing). But you need to tell the model how to use the results of Step 1. I can't say exactly the best way to do that because I don't have the particle tracing module. But my first guess would be to load the x,y, and z electrostatic E field components from Step 1 into the "Electric Field" under the "Electric Force" settings for charge particle tracking, to be executed next in order in Step 2. I think I would make these both part of a single "study," by the way, where Step 1 includes (has checked) only the electrostatic physics (under Physics and Variable Selection) and Step 2 has only the Charge Particle Tracing likewise checked. But there could be other ways. Anyway, I encourage others here who have used the particle tracing package to offer their (likely better) ideas based on their greater knowledge and experience. Good luck.