A surface wave plasma (SWP) source having 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. 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. A mode scrambler coupled to the plasma surface of the EM wave launcher, and configured to reduce mode jumping between the desired EM wave mode and another EM wave mode.