problem with parse_B_ext_grid_function

[Aquios7]

I have a problem with my b-field expanding throughout the entire gridspace when I have it mapped to a specific area in the simulation.

I am trying to put together a simulation that has a plasma enter a b-field that begins at x=0 and scales up in the x direction to a specified number, and on the 0 step the field is correct. The issue comes in the following steps when the b-field seems to expand out from the zone it is set to in the expression, which doesn't seem correct to me from a physics standpoint.

I've added images of the code that I believe may be the problem and I wanted to know if there is a way to fix this or if this is how the field works and I'll try to adjust around it.

Thank you in advance.

[roelof-groenewald]

Hi @Aquios7.

If you want to just have a static B-field you can simply apply the B-field to the particles (see the docs here) instead of writing the B-field to the grid. The By_external_grid_function functionality you are using is supplying initial conditions for the B-field, which is then evolved in time using Maxwell's equations.

[Aquios7]

Thank you for explaining why the field was moving over time.

If I apply the b-field to the particles, then I don't believe a high beta plasma would be able to affect the b-field. If there isn't a way for the particles to affect the b-field over time then I may have to change how I'm going about my simulation.