Plasma reactor coil magnet

A method for processing a workpiece is carried out with a plasma derived from a process gas in a plasma chamber of a plasma processing apparatus during a plasma processing operation. The apparatus includes an array of electromagnets mounted circumferentially around the plasma chamber. The method comprises generating a plasma from a process gas within the chamber and causing plasma particles to strike the workpiece, selecting distributions of current signals for the electromagnets, and applying each selected distribution to the electromagnets to impose more than one magnetic field topology on the plasma during the plasma processing operation.