The medium energy beam transport (MEBT) line for the ISAC radioactive beam facility at TRIUMF requires a dual frequency chopper at 5.89 MHz and 11.78 MHz operating in cw mode. Each chopper has two pairs of parallel plates separated from each other by a copper ground plate with an aperture for the beam. The bottom plates are mounted on ceramic bi-pass capacitors where dc bias voltages are applied. The top plates are connected directly to the inner conductor of the rf feedthroughs. Two separate rf amplifiers power the chopper and a combination of dc and rf voltages are employed to produce an 86 ns or a 172 ns time separation between pulses. An aluminum box houses the inductive coils, fine frequency tuners and rf coupling loops for each resonant circuit. The resonant frequencies are determined by these inductive coils in parallel with the capacitances of the rf feedhroughs and the parallel plates. A commercial ceramic feedthrough has been modified to withstand the nominal operating voltage of 7.5 kV. The chopper has been tested and commissioned to full rated voltages and is routinely operated with beam. 2 DESIGN OF THE CHOPPER The choppers employ lumped circuit components to obtain the desired resonant frequencies of 5.89 MHz and 11.78 MHz. Each parallel plate resonant circuit consists of a water cooled inductive coil, the capacitance of the chopper plates and the capacitance of the feedthrough assembly. The inductive coils, made from hollow ¼” o.d copper tubes, are housed in an aluminum box (36”X12”X12”) and are connected to the rf feedthrough via a rigid coaxial transmission line. The coaxial line is designed to support the coil box above the other beam line components. Water cooling is provided to the ceramic rf feedthrough via the inductive coils. The coupling loops and motor controlled fine frequency tuners are also housed in the same box. The chopper plates, which are 3”