How to set up dielectric waveguide in CST

I want to carry out the dielectric waveguide at CST (outer radius = 1mm, inner radius = 0.5mm, length = 1000mm), center frequency at 120GHz
But I failed many times, so would like to ask the right steps
Can anyone help. Thanks

you decrese number of pulses to setup solver
ex) default is 20 -> 0.1 or 0.01