Abstract: A plasma source is described, comprising a discharge chamber (1) bounded by a base wall (5) and by a lateral wall (3), a system (7) for the admission of gas into said discharge chamber, a system of electrodes (13, 15) which are associated with said discharge chamber (1) and which are connected to a radio-frequency generator (17), and which apply an oscillating electric field within the discharge chamber, and means (9, 11) for generating a static magnetic field in said discharge chamber. Coaxially with said discharge chamber (1) there are disposed a first and a second electrode (15; 13; 13X), at least one of which has an annular extent and is disposed in an intermediate position along the axial extent of the discharge chamber, said two electrodes (15; 13; 13X) being connected to two poles of the radio-frequency generator.