how to assign a current source with 50 ohm in HFSS

I am simulating a power bus using HFSS. The excitation is a current source with 50 ohm resistor in parallel. How can I assign the current source? I cannot find where to set the impedance of the current source.

I also tried to use a lumped port. Can anyone tell me how large the voltage provided by the lumped port is?

Thanks.