Giaccone, B. Berrutti, P. Martinello, M. JACoW Publishing Geneva, Switzerland A collaboration between FNAL, SLAC and ORNL is working to develop plasma processing for 1.3GHz LCLS-II cavities. Key strength of this technique is that it can be applied in situ inside the cryomodule to mitigate field emission due to hydrocarbon contamination. A new method that uses Higher Order Modes has been developed at FNAL for plasma ignition and plasma transfer inside the 9-cell cavity. Plasma processing has been applied to multiple single cell and 9-cell cavities showing positive results; its effectiveness is discussed in terms of Q and Radiation vs E performance before and after processing.