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How to break a charged particle/ion into two particles at any point within the model domain?
Posted 12 ago 2021, 07:29 GMT-4 Low-Frequency Electromagnetics, Charged Particle Tracing, Plasma Physics 2 Replies
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Hello everyone,
I have been using COMSOL 5.6 for my research project. I have come upon a situation in which I need to trace the trajectories of FRAGMENTING charged particles under the influence of an electric field generated between different electrodes at user-defined potentials. I haven't found a single option in COMSOL yet for incorporating the ion fragmentation phenomenon into the model.
The particles released from an inlet are of two different species, some of the particles (not all) of one of those species fragment or break apart into two at a certain point and a certain time inside the model domain between the electrodes during the simulation after release from the inlet. The fragmentation is probabilistic, meaning it has a certain probability of fragmenting under the influence of the electric field when the field's value reaches a certain threshold at a point in the domain, which can be known through electric field distribution. Each of the released species and fragmented particle species has its own charge and mass properties. How do I trace the trajectory of such fragmenting particles in the model? How do I incorporate mid-way fragmentation of a charged particle in the model? All I need to know is how I can make a parent particle disappear and children particle appear (each with certain properties) at any point in the domain during the simulation.
Thanks in advance, Tonu
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Hi Tonu,
The Charged Particle Tracing interface includes a Collisions node that can randomly make particles change direction, as if they collided with molecules in the ambient gas.
After you add the Collisions node, right-click it and you can choose between different types of collision, such as elastic collisions and charge exchange reactions. Some of these collision types, such as Ionization, can trigger the emission of secondary particles when they occur. These secondary particles are allowed to be a different species than the original particle. For instance, the Ionization node applies to electrons and can release both secondary electrions and a heavy ion.
The probability of a particle experiencing a collision is a function of the number density of the gas, and of some collision cross section data that you must provide.
A good starting point is this blog post and the accompanying model "Neutralization of a Proton Beam Through a Charge Exchance Cell":
https://www.comsol.com/blogs/modeling-beam-neutralization-with-a-charge-exchange-cell/
A more generic way to cause particles to randomly release secondary particles is the Velocity Reinitialization node, which you can right-click to add Secondary Emission subnodes.
If you have further questions, please reach out to us at support@comsol.com . Hope this helps!
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Hi Christopher,
Thank you so much for the help. The Velocity Reinitialization node did it for me. I entered an expression in the Velocity Reinitialization Condition to be able to match the conditions in my simulation model and added secondary emission nodes corresponding to each fragment and it worked. Thank you so much. :-)
Warm regards, Tonu Dutta