1. In combination, a vacuum plasma chamber for processing a workpiece, the chamber including a reactive impedance element for electrical coupling with gas in the chamber and for connection to a first, relatively high frequency RF plasma excitation source and an electrode for carrying the workpiece and for electrical coupling with gas in the chamber and for connection to a second, relatively low frequency RF bias source; and a filter arrangement connected to the reactive impedance element and the electrode, the filter arrangement being such that current at the second relatively low frequency flows from the electrode to the reactive impedance element without being substantially coupled to the first, relatively high frequency RF source and current at the first, relatively high frequency that flows from the first, relatively high frequency RF source is substantially prevented from flowing to the electrode and to the second, relatively low frequency RF source.