Setting up fluence

Dear all,
I am an undergraduate working on a summer project. I am new to allpix squared and would like to investigate how radiation fluence affects pixel detector outputs. However, I am not sure how to input the amount of fluence a detector has been subjected to into my .conf file. I would be very grateful if someone could walk me through where I should set up my trapping model and fluence value, or share a configuration file which does that so I could study it.
Thank you!

Dear @PixelEnthusiast ,

The trapping model and irradiation fluence is set in the propagation step, so for example in [GenericPropagation].
The available models are listed here, and they all require the fluence to be given as well.
The documentation for the [GenericPropagation] module provides some more info on how to set it up in the configuration; GenericPropagation | Allpix Squared

An example configuration could be

temperature = 293K
trapping_model = "ljubljana"
fluence = 1e15neq/cm/cm
charge_per_step = 5
integration_time = 25ns

Note the units on the fluence (and, as a general tip, always include units in the configuration to avoid unexpected values; the default units may not be what you want).

Kind regards,

Hi @PixelEnthusiast @hwennlof

in addition to the actual trapping model and the fluence, you should also take care to have an electric field that matches the expected field configuration in your detector after receiving the fluence.

This could either be the output of a TCAD simulation, or, more simplistic, a parabolic function which roughly describes a double-peaked electric field.

Best regards,

Thank you very much Håkan and Simon! I will try that today.

Dear All,

Having set up a fluence in my general .conf file, and having set up a parabolic simulated magnetic field based on a graph I found in a book, I am encountering the following issue. The process runs normally, but at the end it displays “(WARNING) Unused configuration keys in section GenericPropagation: detector 1: fluence”.

The setup of the Generic Propagation is


type = “cmsp1”

temperature = 293K

trapping_model = “ljubljana”

charge_per_step = 10

integration_time = 25ns

Electric Field


model = “parabolic”

minimum_field = 5000V/cm

minimum_position = 50um

maximum_field = 15000V/cm

Dear @PixelEnthusiast ,

I don’t manage to reproduce this with your configuration, I’m afraid. Are you also adding the fluence keyword? From this configuration, if anything, I’d expect trapping_model to be an unused configuration key, if my guess that this may be down to the used Allpix Squared version is correct. What output do you get if you do allpix --version?
The radiation-induced trapping simulation was not included in the framework until version 2.3.0.

Kind regards,

Thank you for your response, it turns out the version of allpix squared was 2.2.1, whcich seemed to be the issue. I am currently using a more modern version and the trapping model is no longer ignored.

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