Basics of the basics

[Plasma-Rob]

I'm interested in modeling plasma from a physics and chemistry perspective. Is Zapdos an appropriate option? My first question is can I get an estimated ion density between two plasma sources if I know the gas, pressure, power, and the geometry? If so, where do I start to learn how to accomplish this? I'd like to do 1D, then 2D. Any thoughts on where to get started would be helpful.

[csdechant]

Yes, I believe Zapdos is a appropriate option for modeling plasma physics and chemistry. Zapdos (along with coupling other physics modules within the MOOSE ecosystem, like CRANE) has be used for simulating plasma-water interaction for atmospherics plasma in 1-D and CCP plasma at mid-low pressures (0.1 - 1 Torr) in 1-D & 2-D. Here is a link to previous publication, with the exception of a few papers currently under review. Some of the current research with Zapdos involves microwave discharges and atmospheric plasma jets.

For the question about ion density; yes, Zapdos can estimate the ion density. The only caveat being that Zapdos currently does have power has in input parameter, but instead, it uses an input voltage. That being said, Zapdos is open-source and is continually being developed on, so any missing physics or capabilities can be added by individual user or addressed in the Issues tab of GitHub.

For where to begin with Zapdos, we have a tutorial directory within Zapdos. These tutorial have user change different parameters within the input files to see how that affects different physical phenomena. For additional information, there are several files in the doc directory mentioned in README.md.

@cticenhour please let me know if I may have miss any other source of information for Zapdos, or if you would like to add anything.

[Plasma-Rob]

Thank you for the clarification and the links and again, thank you for taking time to respond. This is very helpful. I've looked at the zapdos mesh and I'll order the book. I know tutorial 4 isn't the timing test... thanks for humoring me. S.S's M2 did it in 410s though, so I've used it as a speed test to see if my system is commensurate. I'll scour that example more thoroughly.

Made a mesh with gmsh... probably overkill for a 1d case, but not for a 2D case. How do I plug that 1D mesh into a capacitive argon plasma at 10 mTorr with 13.56mHz and say 1000 V with ground on one end? What are the other available options included in the program for types of discharge besides capacitive?

I'll run it again and use paraview to see the changes. I'm running zapdos on a standalone via ssh, so I have to push the model file and pull the data to view. Is there a recommended way to do that?

[csdechant]

To answer your question a little out of order:

• To change the pressure to 10mTorr in Tutorial 4, you would need to change all pressure dependent values. This includes the background gas density (lines 139-146), the electron material properties (line 228 - 248), and ion mobility and diffusivity (lines 255 - 256). All of these relationships are assumed to be linear with pressure and currently they are set to 1Torr (so all the values need to change by a factor of 100).
• To change to voltage in Tutorial 4, you need to change the function of the voltage on line 150 -153. The voltage for this simulation has a function Dirichlet BC on the applied voltage side (which function currently represents a driven voltage at 13.56 MHz 100V peak to peak in the form of $V = 0.100kV * \sin(2\pi * 13.56e6Hz * t)$ . The ground voltage on the other side is done by applying a Dirichlet BC set to zero.
• If you want to look at changing the mesh, I would recommend modifying Tutorial 6. The reason being is that Tutorial 4 reads its mesh information and initial conditions from a previous output file 'RF_Plasma_WithOut_Metastables_IC.e'. Tutorial 6 is the same as Tutorial 4 (a CCP argon plasma) but has less preset inputs, so user has more options to change stuff (like the meshing). The mesh information is located in the Mesh Block (lines 19 - 39 in 'RF_Plasma_Blank.i' in Tutorial 6).
• In the past, we have mainly looked at CCP (such as DC pin-to-plate or RF parallel-plate like the GEC reference source) for verification and validation. We also have capability for 1-D DBD discharges and surface charge effects (we don't have a tutorial for that, but the test file is /test/tests/surface_charge/dbd_mesh.i). By coupling in other MOOSE modules (such as the electromagnetic and Navier-Stokes module), we are currently looking at microwave discharges and plasma jets. To clarify, there is no direct option within Zapdos to declare a discharge type. Discharge types are define by what type of boundary conditions are used. For more information on the difference boundary types within Zapdos, I would recommend looking at the Zapdos PDF file. Also, since Zapdos is based on the MOOSE framework and if you are not familiar with the layout of MOOSE, I would recommend chapter 3 of Alex Lindsay's PhD dissertation and the MOOSE tutorial videos.
• If you are using a ssh, does the server you are connecting to house any visualization options to read exodus file and can you use any GUI options (like xrdp)? If not, you can try coping the output life to your local machine with the scp commend.

[Plasma-Rob]

This is great. Thank you! A couple easy follow up questions and then I'll need to do some testing.

1. Pressure is changing by a factor of 10, not 100, is it a square function? Asking for when I change it to something else.
2. What does BC stand for?

Thanks for the links to the PhD dissertation and videos.
The plan was to use scp to transfer the output files to the local machine for visualization. Paraview downloaded...

[csdechant]

For your questions:

1. The default pressure of Tutorial 4 is 1 Torr. In the previous set of questions, it was asked to change it to 10 mTorr. That should be a factor of 100 decrease in pressure (unless there was a typo).
2. BC stands for Boundary Condition.

Hope testing goes well. As @cticenhour stated before, please start a new discussion thread for any unique question you have.

[Plasma-Rob]

Both super obvious questions. Thanks for stooping to answer. I think in mTorr, so that is where 10 vs 100 comes from...

I think the major answer to all my questions for fundamentals is the moose tutorial. It is 11 hours long and I'm only a couple hours in, but it shows where zapdos is and how this process is set up to work. I did not understand how zapdos calls on moose and this tutorial helps show that with another package. I did not understand that relationship clearly, which led to my zapdos specific question, which was really a moose question. The tutorial illustrates the process to set up the input file and the importance of fundamentally understanding the governing equations. Thank you for answering my questions.