Change voltage on IC, but gain remains the same

I use Garfield++ to simulate the free air ionization chamber. The high voltage between the two plates is 1000V, while the distance between two plates is 6mm,the incoming particles are protons, the gain is about 120. As is known,the working voltage of ionization chamber is in the ionization chamber area, as the voltage increases, it will enter the proportional area, so it`s no longer suitable for an ionization chamber to work.
Now I have the problem that, no matter how high(10000V) or how low(0.1V) I set the voltage between the two plates, the gain remains the same, which is contrary to common sense.
I wonder whether I set the operating conditions less than it needs, did I miss some settings?
I upload the program, and mark red the voltage setting.


from the screenshot you sent the way you set the potential at the electrodes looks fine. Can you post a minimal example that reproduces what you observe?



Thanks for offering help~

In my email attachment, “EleDiffusion2” is the program, “result” is the picture. In the “result” picture, there is a parameter in the upper right corner called “entries”, that means if the number of proton entering the IC is 1, there will be 128 electrons generated, which is the gain of the IC. By running this program for about 100 times, I calculate the average of 100 “entries” as the gain of the IC.

The problem is, no matter what the voltage is, the gain remains around 120.

In my expectations, as the voltage increases to a critical value, the gain would increases obviously. However, this didn`t happen.

That bothers me, do I miss some settings in the program?


Charles Xie

EleDiffusion2.cpp (3.88 KB)

can you replace DriftElectron by AvalancheElectron and give it another try? DriftElectron simulates only the trajectory of the initial electron, while AvalancheElectron also simulates the secondary electrons produced in the avalanche.

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Thanks for your advice, I`ll give a try~

Charles Xie

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