A method for depositing a coating using a magnetron sputtering apparatus and a magnetron sputtering apparatus comprising: a support structure comprising a hollowed shaft comprising a central conduit having a longitudinal axis; a sputter target material defining a bore which is external to the central conduit, the bore also having the longitudinal axis a magnet assembly supported about the support structure, the magnet assembly having a first end, a second end, and a plurality of magnets supported therebetween and being effective, upon rotation, to generate a circumferential external magnetic field about the sputter target material; a first sealed end extending radially inward from adjacent the sputter target material proximate the first end of the magnet assembly and a second sealed end extending radially inward from adjacent the sputter target material proximate the second end of the magnet assembly, wherein the first sealed end, the second sealed end, and the sputter target material seal the magnet assembly therebetween; a cooling system comprising one or more coolant passage extending through the magnet assembly, the central conduit comprising a coolant inlet and a coolant outlet at the first sealed end; and, one or more rotors supported about the support structure and rotatable therewith by coolant passing through the one or more coolant passages.