A process for modifying a surface of a substrate is provided that includes supplying electrons to an electrically isolated anode electrode of a closed drift ion source. The anode electrode has an anode electrode charge bias that is positive while other components of the closed drift ion source are electrically grounded or support an electrical float voltage. The electrons encounter a closed drift magnetic field that induces ion formation. Anode contamination is prevented by switching the electrode charge bias to negative in the presence of a gas, a plasma is generated proximal to the anode electrode to clean deposited contaminants from the anode electrode. The electrode charge bias is then returned to positive in the presence of a repeat electron source to induce repeat ion formation to again modify the surface of the substrate. An apparatus for modification of a surface of a substrate by this process is provided.