[Archive] Plasma Potential

Message by abul anuar:
i’m trying to look at the plasma potential drop for an object at a distance of more than 1 debye length. for example, a circle of radius 0.1*debyeLength in a computation box of length 10*debyeLength.
I used values in the IEEE paper by Alain Hilgers when he verified the SPIS with OML approximation (2008) for the input of my plasma parameter (as comparison). I assume he used GlobalMaxwellBoltzmannVolDistrib as the distribution type.
For a 0V sphere immersed in the mentioned plasma, my simulation resulted in plasma potential values at the edge of the box of up to the power 31 volt (-1e31V) which is ridiculous since we all know that at that distance it should be closed to 0V. I wonder if there is limitation on the computational box because when i reduced the box size to around 1*debyeLength, it produces a resonable results (-2.5V at the sphere surface and close to 0 at the edge). In the paper however, the first results is obtained using computation box of almost 5 times the debyeLength (see values below).
Can anyone suggest what is wrong with my simulation? I include the plasma parameter from the paper if anyone want to have a look. Sphere radius = 0.25m, debyeLength = 2.35, ne = 1e7, T = 1eV. box diam = 20m. Plasma distrib = GlobalMaxwellBoltzmannVolDistrib.
I also found out that if i changed to PICVolDistrib, it produced more appropriate result. i’m using the SPIS4.RC3 version.

Message by abul anuar:
I found out that if i set my computation box greater than one debye length, i’ll start to get funny values for the potential. The larger the computation box, the funnier the potential values become (at 10 debye length i’ll get around 1e31V ). can any one confirm they are getting the same result and if so, what actually happen?

Message by Ignacio Rocca:
Dear abul, how are you?? I understand that the recommended value is 1/4 x debye length for the radius for the external sphere or plasma volume. Please someone of the SPIS can let us know why because I don’t have the phisical explanation!.
Best Abul

Message by Gethyn Lewis:
Hi Abul & Ignacio,
Can you confirm, are you saying that the outer boundary must be 1/4 x debye length? Surely this doesn’t make sense. I would expect the boundary to be about 5 x debye length or at least 1 x debye length.