A Faraday system for measuring ion beam current in an ion implanter or other ion beam treatment system includes a Faraday cup body defining a chamber which has an entrance aperture for receiving an ion beam, a suppression electrode positioned in proximity to the entrance aperture to produce electric fields for inhibiting escape of electrons from the chamber, and a magnet assembly positioned to produce magnetic fields for inhibiting escape of electrons from the chamber. The chamber may have a relatively small ratio of chamber depth to entrance aperture width.