An inductively coupled plasma source is provided with a peripheral ionization source for producing a high-density plasma in a vacuum chamber for semiconductor wafer coating or etching. The source has a segmented configuration with high and low radiation segments and produces a generally ring-shaped array of energy concentrations in the plasma around the periphery of the chamber. Energy is coupled from a segmented low inductance antenna through a dielectric window or array of windows and through a segmented shield or baffle. An antenna for the source is provided having concentrated conductor segments through which current flows in one or more high efficiency portions that produce high magnetic fields that couple through the high-transparency shield segments into the chamber, while alternating low efficiency conductor segments permit magnetic fields to pass through or between the conductors and deliver only weak fields, which are aligned with opaque shield sections and couple insignificant energy to the plasma. Conductor cross-sectional area or turn density differences may be used to distinguish high and low efficiency sections of the antenna conductor. Coil loops are provided in the high efficiency sections to locally increase inductance.