Dust in AstroBEAR - Update 2020/09/28

Objectives

  • Debugging + visualising

Progress:

  • Gas Drag: No progress on gas drag because I was busy with other stuff. Here's a quick recap of the current state of the routines: Both plasma and collisional drag are implemented however I think that the plasma drag is too strong so I need to check that. Could be related to the grain charge routine (which I suspect is buggy and might be the cause of several issues I see in other routines as well). ​Here's the lastest video showing a comparison between the different drag routines.
  • Sputtering: No progress on sputtering either because I was busy with other stuff. Here's a quick recap of the current state of the routines plus a new plot made with the analysis script (see below): Sputtering routines are fully implemented but need debugging. I think that currently, the growth vs destruction rates are not right, probably because of the grain charge routine. ​Here is a recent video showing the destruction of grains during a simulation. With the analysis script, I can also get the ​total dust mass over time in all bins (​UPDATED PLOT) and the ​dust mass per bin over time. Both I think progress too quickly and are too smooth which again points to destruction/growth rates being off.
  • Dust Collisions: Grain-grain collisions are now fully implemented (see ​here and ​here for theoretical background). The code currently crashes after a couple of timesteps because the collision probability starts to exceed realistic thresholds. Might be due to the grain charge routine which I'm planning to start debugging next.
  • Gas Feedback: Gas feedback is done except for gas drag (which is also "done", I'm just not too happy with it and would like to redo that at some point). There's now a gas feedback flag that can be set in the physics.data input file which turns the gas feedback either on or of. If the gas feedback is off, the gas will affect the dust (depending on other flags set) but the gas will not know that there is any dust in the domain. If gas feedback is on, the gas and the dust will affect each other (which I think no previous study has been able to do within the MHD sim.). The following is currently included in gas feedback:
    • for the gas drag, the energy transferred to the dust grains as they are accelerated due to interactions with the gas atoms is removed from the gas energy field
    • for sputtering, the dust that is sputtered to very small sizes is assumed to become part of the gas. If gas atoms are accreted, they are removed from the gas budget in the active cell. This means the overall mass is conserved. (If gas feedback is off, the "destroyed" dust is stored in the lower collector bin. Mass is therefore not conserved in the simulation but we can check the lower collector to make sure all lost mass is accounted for.)
    • for ion trapping, the gas atoms that are trapped in the dust are removed from the gas. If this is not done, the dust would just keep trapping more and more gas atoms and continue to grow.
    • for grain-grain collisions the grains broken into really tiny pieces are assumed to become part of the gas as well just like for sputtering.
  • Analysis Scripts: I've finished the first version of my analysis scripts that will be used to visualise the dust mass evolution in the simulations. It's a bit rough and plots don't look too neat but it will now be easier to understand the overall dust content. The script requires little user input and gets all information from the initial data files and the output. It'll be part of the dusty AstroBEAR version so people using it will have access to it.

Next steps:

  • Debugging
  • Improve analysis script

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