A plasma source generates a plasma beam that is extracted from a plasma generated by electric and magnetic fields. An RF electrode device includes an excitation electrode having an excitation area, and a plasma space is arranged between extraction electrode and excitation area. The plasma, relative to the extraction electrode is at a higher potential which accelerates positive plasma ions, and the plasma and the extracted plasma beam are influenced by a magnetic field. At least one magnet north pole and one magnetic south pole generate the magnetic field. Each are arranged such that a curved magnetic field projecting into the interior of the plasma space is formed. At least one of the north or south poles is embodied in elongate fashion to form a tunnel-like region in the plasma, in which charged particles are held and along which the latter can propagate.