A quadruple electromagnetic coil array coaxially arranged in a rectangular array about a chamber axis outside the sidewalls of a plasma sputter reactor, preferably in back of an RF coil within the chamber. The coil currents can be separately controlled to produce different magnetic field distributions, for example, between a sputter deposition mode in which the sputter target is powered to sputter target material onto a wafer and a sputter etch mode in which the RF coil supports the gas sputtering the wafer. The coil array may include a tubular magnetic core, particularly useful for suppressing stray fields. A water cooling coil may be wrapped around the coil array to cool all the coils. The electromagnets can be powered in different relative polarities in a multi-step process.