Instability using PDE module

Hi all,

As beginner with COMSOL I'm having a problem with the stability of my COMSOL results.
In the PDE module I try to solve four coupled differential equations regarding a MHD flow in an annular channel. At one boundary, the velocity profile shows oscillations. Increasing the mash results in stronger oscillations in a smaller region. Does someone have a suggestion how to suppress the oscillations without simply working with a finer mash?

Thanks,

Peter