We will describe the operation of a cw rf driven multicusp ion source designed for extraction of high current hydrogen and deuterium beams. The source is driven at 2 MHz by a 2.5 turn induction antenna immersed in the plasma. Bare stainless‐steel and porcelain‐coated Cu antennas have been used. The plasma load is matched to the rf generator by a variable tapN:1 transformer isolated to 46 kV, and an LC network on the secondary. With H2gas the source can be operated at pressures between 5 and 60 mT with power reflection coefficients <0.01. The extracted ion current density with a porcelain‐coated antenna is approximately given by 35 mA/cm2/kW with an 80 G dipole filter field for input powers from 3.5 to 6.6 kW. The current density remained constant for operation with a 6 and an 8 mm aperture. The source has been operated for 260 h at 3.6 kW with a single‐porcelain‐coated antenna. Mass spectrometer measurements of the extracted beam at this power show a species mix for H+:H+2:H+3:OH+of 0.49: 0.04: 0.42: 0.04. The calculated beam divergence using the IGUN code is compared with the measured divergence from an electrostatic sweep emittance scanner designed for high‐power cw beam diagnostics. Phase space measurements at 40 kV and 23 mA beam current result in a normalized rms emittance of 0.09 &pgr; mm mrad. ©1996 American Institute of Physics.