A modular plasma source assembly for use with a processing chamber is described. The assembly includes an RF hot electrode with an end dielectric and a sliding ground connection positioned adjacent the sides of the electrode. A seal foil connects the sliding ground connection to the housing to provide a grounded sliding ground connection separated from the hot electrode by the end dielectric. A coaxial feed line passes through a conduit into the RF hot electrode isolated from the processing environment so that the coaxial RF feed line is at atmospheric pressure while the plasma processing region is at reduced pressure.