How to force COMSOL to find plasmonic modes of a waveguide instead of all other non confined modes?

Dear All,

I use electromagnetics eigenfrequency modal analysis to find plasmonic modes of a circular metalic waveguide whose radial pattern is in modified bessel form, but I know that the structure have many other non confined modes with bessel pattern in radial direction, I want to force the solver to find only confined plasmonic modes, How can I do so? Any suggestions?

Thanks,