[Archive] Langmuir probe test - convergence problems

Message by Torbjorn Sundberg:
Hello SPINE!
I’ve been doing some test runs with the new SPIS version (3.6). I like the software but I’ve run into some problems that I need some help sorting out:
My initial tests have been to simulate a langmuir probe and to compare the SPIS value of I and V to my analytical values.
For some reason, I haven’t been able to make the voltage level converge - it just drop linearly. By doing some attempts with varied initial potential, It seems to me that the convergence potential lies somewhere between -500 and -1000 V (which just doesn’t seem reasonable!)
I have tried varying the following to see if they would make any difference, but so far without any success:

  • mesh size
  • size of the plasma sphere
  • particles per cell

Group settings: spacecraft
  • ITO shade
  • spacecraft default plasma
boundary - boundary default plasma volume - plasma model in volume plasma settings: ni = ne = 10^6 Ti = Te = 30 eV
You can find more comments, the geometry file and a sample run at: \http://www.staff.alfvenlab.kth.se/torbjorn.sundberg/spis \http://www.staff.alfvenlab.kth.se/torbjorn.sundberg/spis/2sphere2 So.. Does anyone have any idea on how to interpret this, or is there perhaps some crucial parameter that I might have missed or misused?

Kind regards,

Message by Jean-Francois Roussel:
It looks strange, it should work.
I can suggest you try starting from an example in the Data directory(e.g. Data\ValidationTest\test3_sphere_low_resol, where you’ll need to increase duration (and maybe plasmaSpeedUp to reduce CPU time), then maybe improve statistics with more particles, switch to Boltzmann electrons…)