Patent ID: 8741115

Claim:
A method for applying a sputtered coating onto the interior non-cylindrical surface of a hollow elongate workpiece, the workpiece having a longitudinal axis, the method comprising the steps of: a. providing an elongate emitter assembly, the emitter assembly comprising: i. an elongate cylindrical emitter having a longitudinal axis, the emitter being in the form of a tube having an inner bore; ii. a magnet assembly for providing a magnetic field exterior to the emitter, the magnet assembly having two ends and being located within the inner bore of the emitter, the magnet assembly comprising: at least one magnet unit, the magnet unit comprising at least one electromagnet, where the number of magnet units and the number of electromagnets in each magnet unit is selected so that the magnet assembly comprises a plurality of electromagnets; and at least one nonmagnetic spacing connector between neighboring electromagnets wherein each electromagnet comprises an electrically conductive coil and a hollow core of magnetic material, the longitudinal axis of the coil and core lying along the longitudinal axis of the emitter and the core having a central portion around which the coil is located and two end portions connected to the central portion, the maximum outer diameter of each end portion being greater than the outer diameter of the central portion, the outer diameter of each end portion being equal to the outer diameter of the central portion at the connection of each end portion to the central portion and each end portion being tapered towards the central portion adjacent to the connection of each end portion to the central portion; iii. at least one adjustable source of electrical current, the number of current sources being equal to the number of magnet units, each current source being connected to a different magnet unit; and iv. at least one nonmagnetic end connector at each end of the magnet assembly; b. positioning the emitter and the magnet assembly of the emitter assembly within the workpiece so that the longitudinal axis of the emitter is coaxial with the longitudinal axis of the workpiece; c. providing a low pressure environment containing a sputtering gas exterior to the emitter and interior to the workpiece; d. creating a plasma field between the emitter and the workpiece; and; e. creating a magnetic field exterior to the emitter by flowing current through the electromagnets of the magnet assembly to create a magnetic flux which primarily exits the outer faces of the end portions of the cores of the electromagnets, wherein the magnet assembly configuration and the current supplied to each magnet unit is selected to provide a magnetic field configuration compatible with the workpiece surface contour.