Design and fabrication of FRIB normal conducting cavities

The FRIB (Facility for Rare Isotope Beams) CW linac is based on 326 superconducting cavities, a normal conducting RFQ, and eight normal conducting bunching cavities. Five unique designs were developed for a 40.25-MHz Multi-Harmonic buncher (MHB), 80.5-MHz quarter-wave cavity MEBT bunchers, 161-MHz H-type cavity bunchers, 322-MHz H-type bunchers, and a quarter-wave 161-MHz buncher for a ReAccelerator. The cavities are made of high-purity copper using high-temperature furnace brazing. They are equipped with motorized tuners for real-time frequency control. An efficient water cooling is provided for CW operation. We have developed and applied a multi-step brazing technique to achieve high dimensional accuracy, reliable RF contacts, and accommodate large stainless steel-to-copper joints. The paper will cover the main parameters for each type of bunchers, their design/fabrication, cooling design, RF contact design/effectiveness, tuning process, brazing design and fabrication challenges, coupler design, copper-to-stainless steel transitions, etc. The operation status of these bunchers will also be discussed.