Discussion Forum

Hello all,

this is forum is really helpful and it has help to clarify several issues i encountered in my comsol learning, however now I have a question for which I haven't find a clear answer or guidance.

Currently I'm working in an ion extraction system, for which I first solve the electrostatic field with the AC/DC module. There is no magnetic field.

Later on, I generate 3000 particles in the interior surface of a tube 3mm diameter and 30 mm length. The initial energy is set to 0.2 eV and they can go in any direction yet towards the interior of the tube. The tube and its surrounding are set to 60kV and there is an extraction electrode at ground located at 70 mm. The particles get extracted and I score their position, velocities and energy at 1200 mm. The total simulation time is 30 us. More than enough time to extract the particles that are not killed by the walls

All the solvers are the default ones, and the mesh is set to extra fine plasma physics.

My problem is that the energy reach energies up to 64 kV , if I put more particles, the energies reach up to 80 keV, and this is nonphysical at most the energy should be 60keV + 0.2 eV. I have also tried the generation from a disc but the same behaviour occurs.

I tried to refine the mesh, to restrict more the tolerances and change the solver, but basically just by trial and error and some seems to give somewhat better results but I can only solve for 100 particles or less and this is a huge drawback.

If anyone has deal with this type of behaviour I would greatly appreciated any help and/or suggestion, about a method to reduce this huge discrepancy. It is my first time using comsol

Thanks, have a great day.