constraining the range of dependent variables

Hello,

I have implemented an axisymmetric drift-diffusion equation using the equation-based modeling interface in COMSOL 4.3 (incorporating the necessary terms due to the curvilinear coordinates). I have attached a movie of the resulting density profile over time. I am using zero flux boundary conditions. I was wondering if there is a way to define a range (specifically a maximum) for the dependent variable (number density here) so that the peak remains less than a certain value.

Thank you,

Best,
Aryan