The shape of the signal is puzzling

I used comsol to build an ionization chamber model. The model consists of a cathode plate and six pads. Cathode voltage is (-2806V), and all pad voltages are 0V. The working gas is P10. 50 α Particles emerge from the center of the cathode plate in a random direction(-z direction). There is a huge pulse at the tail of the signal on each pad, and some pads even have positive signals. Why does this happen? It doesn’t make sense.

These are the signals of the pads:

I try to add up all the signals of the 6 pads, and the result looks normal:

This is my code:
tpc6pad.cpp (12.3 KB)
Thank you very much for your help.

Hi @Alex_Zhang; maybe @hschindl can help you with the issue that you described.


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