A duoplasmatron ion source with a partially ferromagnetic anode can be used in multiple applications, including the production of negative ions for secondary ion mass spectrometers and particle accelerators. A partially ferromagnetic anode, which may be embodied in a partially ferromagnetic anode insert, includes a ferromagnetic and non-ferromagnetic portions joined together at a juncture, with an ion extraction aperture defined in the ferromagnetic portion and the juncture being laterally offset from the aperture. An asymmetric magnetic field produced by the partially ferromagnetic region facilitates extraction of charged ions from the central, most intense region of a source plasma in the duoplasmatron ion source. A ferromagnetic conical portion of the anode defines the ion extraction aperture in order to maximize the magnetic field in the vicinity of this aperture.