Message by Robert Albarran:
Hi,
I have been modeling non flowing plasma sheaths and it seems that the electron distribution (Global Max Boltz) stabilizes before the ion distribution (PIC). In general, how can I make PIC stabilize faster? Any limitations in stability time when using the non linear poisson solver?
Thanks,
Robert
Message by Jean-Charles Mateo-Velez:
Hi,
the PIC stabilization is at least the time for the ions to travel 2 or 3 times through the domain. Using appropriate values for ionDuration permit to determine how far the ions go at each loop of the plasma solver (Poisson + transport of particles). Fluid Electrons are analytical and always in equilibrium with the potential. If they don’t change, it signifies that the potential neither. As a consequence, in your case, the ion density is not so important for the potential map.
Jean-Charles
Message by Robert Albarran:
I see. So if I use a Global Max Boltz distribution for ions with the linear poisson solver and proper plasmaDt and meshing resolution then the ion density will relax sooner. Is this correct?
Thank you,
Robert
Message by Robert Albarran:
When using PIC ions the probing line filter shows many ‘wiggles’ in the ion density. In particular, it shows asymmetry about a conductor in a non flowing plasma. Although the potential has floated (so I assume it has reached steady-state), the asymmetry in the ion probing line persists. Could this just be attributed to the inherent instability of PIC?
Robert.
Message by Jean-Charles Mateo-Velez:
Boltzman Maxwell model is not expected to provide good results for ions.
Message by Jean-Charles Mateo-Velez:
The wiggles come from the statistics of PIC. To smooth them, you can either increase the number of superparticles used or plot the “final” results which are average 3D values. The asymmetry may have several origins. Plot the density at different times to determine if it changes. Instabilities may come from mesh refinement issues.