Electron endpoints in GEM structure

[bmcconne]

Hi everyone!

I’m working on a Garfield++ simulation to count the number of electrons in different regions of a triple GEM. I’m noticing some strange behavior in my simulations. I tried to attach my minimal working copy, but it says new users can’t attach uploads-- my Github user is bkmcco, and I have uploaded everything necessary to a repository titled “garfield_question”.

1. For some reason, I can’t get the avalanche plot (attached under “avanlanche.png”) to shade in the metal layers on the top and bottom of the GEM. I’ve tried using SetColor with the material number of the metal (1), but it’s not doing the trick.

2. The electrons are exhibiting strange behavior near the holes. There seems to be some sort of flat blockade around z = -0.1005, and the electron appears to be travelling through the GEM layer. I’m wondering if this is just because the GEM is a 3D structure – perhaps the avalanche is travelling through a hole at a different y-position-- but am still not sure why the flat cutoff at z=-0.1005. There are some images attached showing this.

3. In my code, I build a list of every electron with an endpoint with a z-coordinate less than -0.1 (meaning, the electrons that are lost near the bottom of GEM 1). After one run, the list has 450 entries. It seems to me that it is counting every single electron as having an endpoint with z < -0.1?

Thanks everyone for your help!!!

[Danilo]

Adding @hschindl in the loop

[hschindl]

Hi,
the metal regions are usually not meshed and thus not exported from Ansys which makes sense from a performance point of view. If you want to mesh the metal and visualise the elements in Garfield, you’ll need to slightly adapt your Ansys script as in the “Gem Movie” example: Examples/GemMovie · master · garfield / garfieldpp · GitLab

The electrons are indeed travelling through another hole that is not in the viewing plane. The cut off at z = -0.1005 is due to the metal layer.

For your last question, I don’t know. I didn’t see anything obviously wrong in your code. How many electrons do you get in total?

[bmcconne]

Thanks for your quick response, and for the tips on adding the metal regions to my plot.

One of the runs, for example, observed 7271 electrons at readout (after three layers of GEMs). For this same run, the code reports that there were 1623 electrons with endpoints that satisfied z<-0.1. I’d assumed this to be far too high a proportion to be collected on the plates/result of attachment, but it seems all of the relevant endpoints have a status code -5 (meaning that they are being collected on the plates?)