Updating geometry

[mariajmz]

WORK IN PROGRESS, DON'T MERGE

• The remote materials file https://sultan.unizar.es/materials/materials.xml don't work, I replace it with https://rest-for-physics.github.io/materials/rest.xml
• Including explicit units
• In the last version of the geometry (October 2023) I changed the width of the grid in the cathode to 0.1 mm so I have included this change here

This is the status of the geometry right now:

Tasks to update the geometry:

• Check materials?
• Remove the grid (or keep the old geometry and make a new one without grid)
• Reduce drift distance: is this something that is going to change from time to time? We can make different versions of the geometry with different drift distances or make it variable

[mariajmz]

This is the new geometry:

• I use the center of the gas as the reference position.
• I have made the positions of the rest of the elements depend on the gas_length variable, so we can change it (I haven't add the environment variable yet).
• cathode_thickness = 1 mm. Notice that I have made the cathode with the same radius as the inner radius of the vessel (in the real prototype the cathode is smaller)
• I haven't included the sample as a proper volume. It can be added but we can simulate the decays in a "virtual" volume also.

[juanangp]

The new geometry looks nice, but I have some comments that I think should be addressed before deploying:

• I use the center of the gas as the reference position.

I think the reference should be the Micromegas because I am afraid that the reference position won't be fixed for all the simulations because you can run simulations with different drift lengths.

• I have made the positions of the rest of the elements depend on the gas_length variable, so we can change it (I haven't add the environment variable yet).

Same comment here, I don't think is a good strategy to have the reference position moving with the different drift lengths. Also, if you set the reference in the Micromegas you can define your readout in a generic way using the total chamber length since you won't have any events outside of your sensitive volume. Otherwise, you will have to define a readout every time you change the drift length.

• cathode_thickness = 1 mm. Notice that I have made the cathode with the same radius as the inner radius of the vessel (in the real prototype the cathode is smaller)

I think the thickness doesn't matter, but you have to be aware that we are planning to replace the cathode by copper wires. I don't know yet if we are interested in running simulations with this cathode geometry.

• I haven't included the sample as a proper volume. It can be added but we can simulate the decays in a "virtual" volume also.

This is a bit delicated because the samples can have different geometries and can be placed in different positions, so I am afraid we will have to implement the sample geometry separately depending on the measurements. On the other hand, I don't know if a virtual volume is a good strategy because alphas going in the cathode direction can deposit energy in the gas, otherwise the alphas will be absorbed in the sample.

[mariajmz]

New changes:

• The readout is now the reference for the positions of the volumes
• I have included a simple volume for the sample
  • It is placed inside the gas (so is a child volume of the gas)
  • It is important to notice that maybe we will need to change the geometry and material of the sample depending on the measurements.
    My initial idea was to implement the geometry of the sample as an external file, as described here https://geant4-forum.web.cern.ch/t/gdml-modules-help/496 but the use of an external file for the materials is giving problems (you need to include a <material> section inside the gdml that describes the sample)

[AlvaroEzq]

you need to include a <material> section inside the gdml that describes the sample

I don't think that is a problem. It makes sense to me to define the material of the sample in its gdml file.

My initial idea was to implement the geometry of the sample as an external file

I am currently working on how REST parse the gdml modules (subfiles) in this PR, so it will be great to have your feedback there too and solve any issue you encounter with using a gdml module 😄.

[mariajmz]

I don't think that is a problem. It makes sense to me to define the material of the sample in its gdml file.

Yes, that's true, it makes sense. But when I try to implement the material file as external inside the sample gdml:
<!ENTITY materials SYSTEM "https://rest-for-physics.github.io/materials/rest.xml">
and try to read this geometry in ROOT, I get an error related to the external xml file. I have tried to copy the content of the materials xml file directly in the sample gdml and the problem disappears.

I am currently working on how REST parse the gdml modules (subfiles) in this PR, so it will be great to have your feedback there too and solve any issue you encounter with using a gdml module 😄.

Great! I will have a look👍