A rotary sputter magnetron assembly for use in sputtering target material onto a substrate is provided. The assembly comprises a longitudinally extending target tube having a longitudinal central axis, said target tube extending about a magnet array that is configured to generate a plasma confining magnetic field adjacent the target tube, said target tube supported for rotation about its longitudinal central axis and a pair of side shunts positioned parallel to the longitudinal central axis, and on opposing lengthwise sides of said target tube.