One embodiment is directed to a plasma source comprising a cavity and at least first and second electrodes. The plasma source is configured to, during a first portion of each cycle, bias the first electrode as a cathode and use the second electrode as an anode, during a second portion of each cycle, apply an ion flush bias to the first and second electrodes, during a third portion of each cycle, bias the second electrode as a cathode and use the first electrode as an anode, and during a fourth portion of each cycle, apply an ion flush bias to the first and second electrodes. Other embodiments are disclosed.