A surface wave plasma (SWP) source is described. The SWP source comprises an electromagnetic (EM) wave launcher configured to couple EM energy in a desired EM wave mode to a plasma by generating a surface wave on a plasma surface of the EM wave launcher adjacent the plasma. The EM wave launcher comprises a slot antenna having a plurality of slots. The SWP source further comprises a first recess configuration formed in the plasma surface, wherein the first recess configuration is substantially aligned with a first arrangement of slots in the plurality of slots, and a second recess configuration formed in the plasma surface, wherein the second recess configuration is either partly aligned with a second arrangement of slots in the plurality of slots or not aligned with the second arrangement of slots in the plurality of slots. A power coupling system is coupled to the EM wave launcher and configured to provide the EM energy to the EM wave launcher for forming the plasma.