An atmospheric pressure plasma source operated by radio frequency power has been developed. This source produces a unique discharge that is volumetric and homogeneous at atmospheric pressure with a gas temperature below 300 degrees C. It also produces a large quantity of oxygen atoms, similar to 5 x 10(15) cm(-3), which has important value for materials applications. A theoretical model shows electron densities of 0.2-2 x 10(11) cm(-3) and characteristic electron energies of 2-4 eV for helium discharges at a power level of 3-30 W cm(-3). (C) 2000 American Institute of Physics. [S0003-6951(00)01303-6].