Abstract: A substrate support electrode for use in plasma processing equipment has a book-shaped prismatic body containing a magnet core with flange-like pole pieces at each end to provide a longitudinal magnetic field wrapped around the electrode body. An auxiliary field-shaping magnet spaced from a substrate support face of the electrode body, with each of its poles adjacent to the pole piece electrode body with each of its poles adjacent to the of like polarity of the electrode, flattens the magnetic field adjacent to the electrode support surface to produce a thin plasma of substantially uniform thickness close to the electrode surface.