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Appropriate Model For Atomic Beam Simulation
Posted 10.12.2016, 10:42 GMT-5 Fluid & Heat, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 5.2a 3 Replies
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Hi,
I am trying to figure out how to model the behaviour of an atomic beam being emitted from a reservoir into a vacuum system. I have the basic model created in the Free Molecular Flow module, and I can vary the reservoir temperature and various other parameters to change the behaviour of the beam.
What I would like to do though, is include the possibility of the existence of a background (buffer) gas in the system, with a partial pressure variable from, say, 1E-9 mbar up to 1E-2 mbar, and see how different different background pressure conditions affect the propagation of the beam (its shape, its characteristic length, etc).
Does anyone have any advice as to which modules would be the best to use to implement something like this?
I am trying to figure out how to model the behaviour of an atomic beam being emitted from a reservoir into a vacuum system. I have the basic model created in the Free Molecular Flow module, and I can vary the reservoir temperature and various other parameters to change the behaviour of the beam.
What I would like to do though, is include the possibility of the existence of a background (buffer) gas in the system, with a partial pressure variable from, say, 1E-9 mbar up to 1E-2 mbar, and see how different different background pressure conditions affect the propagation of the beam (its shape, its characteristic length, etc).
Does anyone have any advice as to which modules would be the best to use to implement something like this?
3 Replies Last Post 13.12.2016, 10:18 GMT-5
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Posted:
8 years ago
Hi Matthew, there is an example model and app which sounds quite close to what you want:
www.comsol.com/blogs/modeling-beam-neutralization-with-a-charge-exchange-cell/
www.comsol.com/model/neutralization-of-a-proton-beam-through-a-charge-exchange-cell-16631
The Free Molecular Flow interface (Molecular Flow Module) computes the number density in the chamber, and the Charged Particle Tracing interface (Particle Tracing Module) is used to compute the trajectory of the charged and neutral beam.
Dan
www.comsol.com/blogs/modeling-beam-neutralization-with-a-charge-exchange-cell/
www.comsol.com/model/neutralization-of-a-proton-beam-through-a-charge-exchange-cell-16631
The Free Molecular Flow interface (Molecular Flow Module) computes the number density in the chamber, and the Charged Particle Tracing interface (Particle Tracing Module) is used to compute the trajectory of the charged and neutral beam.
Dan
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Posted:
8 years ago
Dan,
Thanks for your reply. This looks like something I can adapt for my situation. I'll try it out.
Thanks for the suggestion!
Thanks for your reply. This looks like something I can adapt for my situation. I'll try it out.
Thanks for the suggestion!
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Posted:
8 years ago
Hi Dan,
I had a look at the model you suggested and it looks like it pointed me in the right direction. To start off with, I have set up a basic "particle tracing for fluid flow" physics node, but it's the first time I've tried it and I am getting mixed results.
The first attached image shows an attempt at replicating the "beaming" effect which I have been able to produce using a very similar geometry in MOLFLOW (molflow.web.cern.ch/). As you can see, most of the collisions are handled fine, but there is one particle which (after several reflections on other faces) passes straight through one of the walls. The second image shows a later timestep, after which several other particles show the same behaviour.
For this test, all walls are set to "Diffuse scattering" with wall accuracy of order 2. The colour scale for the images corresponds to the particle velocity, which is set to Maxwellian.
I'm not sure what the cause of this behaviour is, but it is clearly unphysical and since I'm interested in transmission through the narrow channel, it's quite annoying! I've tried lots of different mesh sizes and time steps but the problem seems to persist. Do I simply need to find the right parameters, or is something else in play here?
The model file (mesh + results cleared for file size reasons- settings as-is take 10s to run on my machine) is attached.
I had a look at the model you suggested and it looks like it pointed me in the right direction. To start off with, I have set up a basic "particle tracing for fluid flow" physics node, but it's the first time I've tried it and I am getting mixed results.
The first attached image shows an attempt at replicating the "beaming" effect which I have been able to produce using a very similar geometry in MOLFLOW (molflow.web.cern.ch/). As you can see, most of the collisions are handled fine, but there is one particle which (after several reflections on other faces) passes straight through one of the walls. The second image shows a later timestep, after which several other particles show the same behaviour.
For this test, all walls are set to "Diffuse scattering" with wall accuracy of order 2. The colour scale for the images corresponds to the particle velocity, which is set to Maxwellian.
I'm not sure what the cause of this behaviour is, but it is clearly unphysical and since I'm interested in transmission through the narrow channel, it's quite annoying! I've tried lots of different mesh sizes and time steps but the problem seems to persist. Do I simply need to find the right parameters, or is something else in play here?
The model file (mesh + results cleared for file size reasons- settings as-is take 10s to run on my machine) is attached.