A rf ion source with a large extraction area suitable for fusion applications is considered. The source is a metallic magnetic multipole bucket with an internal antenna to couple the rf (at a frequency of 2 MHz) to the plasma. The source is diagnosed by an array of Langmuir probes to measure uniformity, density, and temperature and a small probe accelerator to extract a negative ion beam. A two-turn antenna is found to couple more power into the plasma than a half-turn antenna. When operated as a negative ion source at low powers, the source efficiency is found to be high and not to have a strong dependence on gas pressure. An extracted negative ion current density of about 4 mA/cm2 at 7 mTorr was obtained when 3 kW of power was coupled into the plasma.
