Beam inclination

psmolyan · April 6, 2025, 9:41am

Dear Allpix experts,

I need to simulate the response of a 2-layer Timepix3 detector to protons at different angles.
In the case of 1-layer detector, I have no problem, the detector can be rotated easily through the geometry file.

But, in the case of 2 layers, I have a problem because I rotate each detector separately relative to their centers, which is not what I need. I need to rotate them as one assembly relatively to the point, which is in between two detectors.

I tried configuring the beam inclination through the GPS file, but it’s kinda complex…

I would be happy to hear your comments and suggestions.

Best regards,
Petr

simonspa · April 7, 2025, 2:26pm

Hi @psmolyan

If you can use a beam source directly, there is the parameter beam_direction (DepositionGeant4 | Allpix Squared) which is a unit vector pointing in the direction of the beam.
If you have to use a macro file to define your GPS, you could look at how we calculate the correct angles: src/modules/DepositionGeant4/GeneratorActionG4.cpp · master · Allpix Squared / Allpix Squared · GitLab

I hope, this helps!

All the best,
Simon

psmolyan · April 10, 2025, 9:09am

Hi @simonspa

Thanks for the suggestions!

As I understood beam_direction is unit vector, so I can’t do arbitrary angle.

So I guess I will go for GPS file configuration.

Thanks.

Best regards,
Petr

simonspa · April 10, 2025, 2:18pm

Hi @psmolyan

the vector is a unit vector since it’s only a direction, but since you can use floating-point values for the entries, any direction is possible.

Also, in the code we will normalize the final vector, so you don’t have to care about the unity when setting the config.

Best,
Simon