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<p class="MsoNormal"><span style="font-size:11.0pt">Hi Cunbo,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">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:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l2 level1 lfo3"><span style="font-size:11.0pt">The Circuit unit solves a set of circuit equations, or simply reads in a data file to get the drive current.<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l2 level1 lfo3"><span style="font-size:11.0pt">The Diffuse unit uses this drive current and Ampere’s Law to set the azimuthal field on the upper-r boundary.<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l2 level1 lfo3"><span style="font-size:11.0pt">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.<o:p></o:p></span></li></ol>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">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/.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">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. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:black">--</span><span style="font-family:"Calibri",sans-serif;color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#181A1B">Eddie Hansen</span><span style="font-family:"Calibri",sans-serif;color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#181A1B">Applications Group Leader<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#181A1B">Flash Center for Computational Science</span><span style="font-family:"Calibri",sans-serif;color:black"><o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">flash-users <flash-users-bounces@flash.rochester.edu> on behalf of Cunbo Liu <lcb1547661952@stu.xjtu.edu.cn><br>
<b>Date: </b>Friday, May 9, 2025 at 4:07 AM<br>
<b>To: </b>flash-users@flash.rochester.edu <flash-users@flash.rochester.edu><br>
<b>Subject: </b>[FLASH-USERS] Inquiry on Implementing Sheared-Flow Z-Pinch Electrode Configuration in FLASH<o:p></o:p></span></p>
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<p><span style="font-size:10.5pt;font-family:SimSun">Dear FLASH Developers and Users,
<o:p></o:p></span></p>
<p><span style="font-size:10.5pt;font-family:SimSun">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. <o:p></o:p></span></p>
<p><span style="font-size:10.5pt;font-family:SimSun">For my sheared-flow Z-pinch study, I am exploring an alternative electrode configuration:
<o:p></o:p></span></p>
<ul type="disc">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l3 level1 lfo6">
<span style="font-size:10.5pt;font-family:SimSun">Inner electrode as a cylindrical shape, located at a specified radius, as shown by the yellow region in the attached diagram.
<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l3 level1 lfo6">
<span style="font-size:10.5pt;font-family:SimSun">Outer electrode located at the radial boundary.
<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l3 level1 lfo6">
<span style="font-size:10.5pt;font-family:SimSun">Current flows radially outward, from the inner "mid-plate" to the edge.
<o:p></o:p></span></li></ul>
<p><span style="font-size:10.5pt;font-family:SimSun">Before modifying the source code, I would like to ask the community:
<o:p></o:p></span></p>
<ol start="1" type="1">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo9">
<span style="font-size:10.5pt;font-family:SimSun">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?
<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo9">
<span style="font-size:10.5pt;font-family:SimSun">Could this setup be approximated by introducing non-evolving plasma species to emulate the electrode behavior?
<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo9">
<span style="font-size:10.5pt;font-family:SimSun">If not directly supported, which routines or files would be best to modify?
<o:p></o:p></span></li></ol>
<p><span style="font-size:10.5pt;font-family:SimSun">Apologies if a similar question has been addressed—I wasn’t able to find one in the archive.<br>
Any guidance or pointers would be greatly appreciated.<br>
Thank you for your time and support.<o:p></o:p></span></p>
<p><span style="font-size:10.5pt;font-family:SimSun">Best regards,<br>
Cunbo Liu <o:p></o:p></span></p>
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