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Particle Tracing: Change variable at specific time
Posted 15.03.2023, 13:52 GMT-4 Charged Particle Tracing, Studies & Solvers, Physics Interfaces Version 5.4 2 Replies
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Hello,
I am using COMSOL 5.4 and am trying to construct a model for an electron beam where the value of an electronic potential changes during operation. In simple terms, I am running the model from 0 to 20 ns and at 10 ns I want to change the electric potential on a surface from X to Y. I am modeling the electron beam through vacuum emitted via thermionic emission and using the Bidrectionally Coupled Particle Tracing study step to obtain the transmitted current from the thermionic emission cathode to a Particle Counter on the anode. According to the theory I am investigating, changing the electric potential should serve to prevent electrons from travelling from the cathode to the anode and thus the transmitted current goes to zero after the electric potential is changed.
I have tried using the Events interface with Explicit events to change the variable, but the events interface returns a warning when used alongside particle tracing. What am I missing?
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Jordan,
you can make the boundary condition time dependent. E.g. V = x(t<=10[ns]) + y(t>10[ns]) You probably need to smooth the expression because the time dependent solver doesn't like instantaneous jumps. Check the built in smoothing functions. Don't use variable names like x, y, etc. They are reserved internally.
Cheers Edgar
-------------------Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
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Jordan,
you can make the boundary condition time dependent. E.g. V = x*(t10[ns]) You probably need to smooth the expression because the time dependent solver doesn't like instantaneous jumps. Check the built in smoothing functions. Don't use variable names like x, y, etc. They are reserved internally.
Cheers Edgar
Hello Edgar,
Thank you for your help (and apologies for the long delay in acknowledging it). You were correct that I needed to use a time dependent boundary condition.
What my issue ended up being was that the Bidirectionally Coupled Particle Tracing only solves the particle tracing in a time-dependent study, so I had to split the study into two steps (Stationary and Time-Dependent) and ensure I was solving for the electric field with time. Obvious flaw once it was pointed out to me by COMSOL tech support, but figured I'd update here for anyone else having trouble like I did.