[FLASH-USERS] Inquiry on Implementing Sheared-Flow Z-Pinch Electrode Configuration in FLASH

[Hansen, Eddie]

Hi Cunbo,

The simplest answer to your question is no, FLASH does not currently have built-in support for this kind of configuration. Here’s broadly how our Z-pinch simulations work now:


  1.  The Circuit unit solves a set of circuit equations, or simply reads in a data file to get the drive current.
  2.  The Diffuse unit uses this drive current and Ampere’s Law to set the azimuthal field on the upper-r boundary.
  3.  From the liner outer radius to the upper-r boundary is a pseudo-vacuum that is given an artificially high magnetic resistivity, so that the implicit magnetic diffusion solver can quickly diffuse in the azimuthal field that was set at the upper-r boundary.

The Circuit part would be easy for your case if you just use FileInput. The challenge would be in setting B-fields at domain boundaries appropriately from a radial current. In my mind, I am picturing this configuration creating -Bphi at the upper-z boundary and +Bphi at the lower-z boundary.But if the magnitude of Bphi has radial dependence, then this complicates things further because you won’t be able to set just one value for a Dirichlet BC. You would at least need to modify routines in Diffuse/DiffuseMain/Unsplit/MHD/.

The closest thing we have to the “non-evolving” plasma thing you want is by using BDRY_VAR. It won’t emulate any electrode behavior (the Circuit unit takes care of that); it simply marks cells as “solid” and does not allow them to evolve via Hydro fluxes.

--
Eddie Hansen
Applications Group Leader
Flash Center for Computational Science


From: flash-users <flash-users-bounces at flash.rochester.edu> on behalf of Cunbo Liu <lcb1547661952 at stu.xjtu.edu.cn>
Date: Friday, May 9, 2025 at 4:07 AM
To: flash-users at flash.rochester.edu <flash-users at flash.rochester.edu>
Subject: [FLASH-USERS] Inquiry on Implementing Sheared-Flow Z-Pinch Electrode Configuration in FLASH

Dear FLASH Developers and Users,

I am currently working on modeling a Z-pinch in the 2D axisymmetric (r–z) geometry. In the default configuration, the axial (z) boundaries act as electrodes, voltage (current) is applied across them, and the return current flows through the radial boundary.

For my sheared-flow Z-pinch study, I am exploring an alternative electrode configuration:

  *   Inner electrode as a cylindrical shape, located at a specified radius, as shown by the yellow region in the attached diagram.
  *   Outer electrode located at the radial boundary.
  *   Current flows radially outward, from the inner "mid-plate" to the edge.

Before modifying the source code, I would like to ask the community:

  1.  Is this electrode configuration supported within the current FLASH framework, or could it be approximated by modifying the existing rectangular boundaries to achieve the desired electrode geometry?
  2.  Could this setup be approximated by introducing non-evolving plasma species to emulate the electrode behavior?
  3.  If not directly supported, which routines or files would be best to modify?

Apologies if a similar question has been addressed—I wasn’t able to find one in the archive.
Any guidance or pointers would be greatly appreciated.
Thank you for your time and support.

Best regards,
Cunbo Liu
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