[FLASH-USERS] [EXT] Re: resistivity problems

[Hansen, Eddie]

Hi Zhao,

I suspect these resistivity values (1.e-20 and 1.e-18) are too low to observe a significant difference in the simulation…

I see in your par file that you specified ‘CGS’ units, so this means that ‘resistivity’ will be multiplied by a factor of c^2/(4*pi) to get magnetic diffusivity eta in terms of cm^2/s.
eta = resistivity*c^2/(4*pi)

Now, as a rough estimate, the magnetic field will diffuse a distance L in a time t according to:
L = sqrt(t*eta)

Your simulation is 4 ns long, so putting this all together:
resistivity = 1.e-20 • L ~ 0.5 um
resistivity = 1.e-18 • L ~ 5 um

Both numbers are smaller than your resolution which has a minimum value of 15.625 um in the z-direction (it’s not absolutely necessary, but I would recommend making resolution the same in each direction if possible). So a couple of things to try:

  1.  increase resistivity
  2.  decrease cell width
--
Eddie Hansen
Research Scientist
Flash Center for Computational Science


From: flash-users <flash-users-bounces at flash.rochester.edu> on behalf of Ryan Farber <rjfarber at umich.edu>
Date: Thursday, May 4, 2023 at 2:03 PM
To: Reyes, Adam <adam.reyes at rochester.edu>
Cc: flash-users <flash-users at flash.rochester.edu>
Subject: Re: [FLASH-USERS] [EXT] Re: resistivity problems
I'm not sure what the typical units / scaling FLASH does for magnetic resistivity, but 1e-18 and below sounds like it's smaller than double point floating precision. At least as another debugging test you might try a value of unity.

Best,
--------
Ryan


On Thu, May 4, 2023 at 7:16 PM Adam Reyes <adam.reyes at rochester.edu<mailto:adam.reyes at rochester.edu>> wrote:
Hi Zhao,

I don't see any issues with how you're setting the resistivity. Are your simulations producing the magnetic fields that you expect? I'm surprised you don't see any differences between the runs at different resistivities.
*************************************************************************
Adam Reyes
[https://flash.rochester.edu/site/common/images/email_signature/FLASH.jpg]
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<mailto:adam.reyes at rochester.edu>
Web https://flash.rochester.edu<https://flash.rochester.edu/>
 (he / him / his)
[https://flash.rochester.edu/site/common/images/email_signature/FLASH-pride-sml.png]
*************************************************************************


On Thu, May 4, 2023 at 10:34 AM 赵旭 <xuzhao1994 at sjtu.edu.cn<mailto:xuzhao1994 at sjtu.edu.cn>> wrote:
Dear Adam,

Thank you very much for your reply.

This simulation is try to use FLASH to simulate the magnetic reconnection in a 'coil' target configuration.

I tried to set the resistivity from 0, 1e-20, and 1e-18 (for testing), respectively.

I want to see the transition from magnetic energy to kinetic energy when the reconnection occurs.

However, it seems nothing changes in these simultions (Both plasma evolution and the value of magnetic energy/kinetic energy).

The log and .par file are attached.

Any suggestion helps as I have struggled for a while for this problem.

Best,
Zhao

----- 原始邮件 -----
发件人: "Adam Reyes" <adam.reyes at rochester.edu<mailto:adam.reyes at rochester.edu>>
收件人: "赵旭" <xuzhao1994 at sjtu.edu.cn<mailto:xuzhao1994 at sjtu.edu.cn>>
抄送: "flash-users" <flash-users at flash.rochester.edu<mailto:flash-users at flash.rochester.edu>>
发送时间: 星期四, 2023年 5 月 04日 下午 9:51:44
主题: Re: [FLASH-USERS] resistivity problems

Hi Zhao,

Do you have a logfile from the FLASH simulation that you could share? These
contain details of how the code was configured for your simulation so we
can give a more specific suggestion.

*************************************************************************
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<mailto:adam.reyes at rochester.edu>
Web https://flash.rochester.edu
 (he / him / his)

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

On Thu, May 4, 2023 at 9:43 AM 赵旭 <xuzhao1994 at sjtu.edu.cn<mailto:xuzhao1994 at sjtu.edu.cn>> wrote:

> Dear FLASH users/developers,
>
>
> When I want to set up a non-ideal plasma magnetic resistivity condition in
> 3D laser-driven experiment simulation, a mistake trouble me.
>
> I change the resistivity of plasma at constant condition, but the
> simulation results didn't change. I use the CGS system. Do I made any
> mistakes in in FLASH?
>
> Any suggestion helps.
>
>
> Zhao
>
> --
> Zhao Xu
> Laboratory for Laser Plasmas (MoE)
> Shanghai Jiao Tong University
> 800 Dongchuan Rd, Shanghai 200240
> _______________________________________________
> flash-users mailing list
> flash-users at flash.rochester.edu<mailto:flash-users at flash.rochester.edu>
>
> For list info, including unsubscribe:
> https://flash.rochester.edu/mailman/listinfo/flash-users
>
--
Zhao Xu
Laboratory for Laser Plasmas (MoE)
Shanghai Jiao Tong University
800 Dongchuan Rd, Shanghai 200240
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