[FLASH-USERS] Current does not flow through areas with high conductivity in flash

[Reyes, Adam]

Hi Lizy,

We have verified the magnetic diffusion for a current drive against some of the solutions derived in this paper: https://www.osti.gov/servlets/purl/1027976

You can always adjust the resistivity of the conducting material to match the physics of what you’re interested in. The constant current density inside the conductor is the equilibrium solution if you’re considering only magnetic diffusion and a current carrying wire, but will always start out concentrated on the surface and diffuse inwards. If you’re not interested in capturing this transient behavior you can always increase the time step, but are always limited by the CFL condition for the hydro solver. 
*********************************************
Adam Reyes


Code Group Leader, Flash Center for Computational Science  
Research Scientist, Dept. of Physics and Astronomy
University of Rochester
River Campus: Bausch and Lomb Hall, 369  
500 Wilson Blvd. PO Box 270171, Rochester, NY 14627
Email adam.reyes at rochester.edu
Web https://flash.rochester.edu
 (he / him / his)


*********************************************



> On May 30, 2024, at 10:13 AM, lizy <3287940670 at qq.com> wrote:
> 
> Dear Flash developers and engineers,
> 
> In two-dimensional axisymmetric simulation, a thin metal wire with high resistivity (diameter of tens of micrometers) flows through a current, and the metal wire is surrounded by a vacuum outside. Within a hundred nanoseconds, the actual situation should be that the current flows through a low resistivity region, but currently, due to the magnetic field diffusing from the outside to the inside, the internal metal diffusion coefficient is too low. Now the current is concentrated at the vacuum metal boundary rather than in the metal region. I used an implicit resistivitySolver, but the final result did not match reality. Is there any good solution?
> 
> In addition, the process of implicit magnetic diffusion should be a solution to the evolution of the global magnetic field, and the magnetic field should have diffused at the initial moment. However, the current implicit magnetic diffusion in flash seems to involve calculating the diffusion of the magnetic field at each time step, resulting in slow diffusion in areas with low magnetic diffusion coefficients. I still don't quite understand the process of magnetic diffusion.  I would especially appreciate your patient answe！
> 
>                                                                          Lizy
> 
>                                                               30,May,2024
> 
> 
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