Abstract: Vapor deposition coating can be performed in apparatus in which a plasma of the coating material is generated from the surface of an electrode. The surface area of the electrode from which the plasma is generated can be selectively adjusted by exposing the plasma generating surface of the electrode to the influence of a magnetic field and adjusting the strength of the magnetic field to spread plasma over the evaporative surface of the electrode to permit more efficient utilization of the electrode. Preferably, the electrode is in the form of a flat metal disc (e.g. titanium) and the magnetic field is generated by a wire coil that substantially encircles or is coaxial to the electrode, with the electrode or an associated element functioning as a core for the coil.