| A next generation Energy Recovery Linac (ERL) is under development in the Collider-Accelerator Department at Brookhaven National Laboratory (BNL). This ERL uses a superconducting radio frequency (SFR) cavity to produce an electric field gradient ideal to accelerate charged particles. As with many accelerators, higher-order modes (HOMs) can be induced by a beam of charged particles traversing the linear accelerator cavity. The excitation of these modes can result in problematic single and multi-bunch effects and also produce undesirable heat loads to the cryogenic system. Understanding HOM prevalence and structure inside the accelerator cavity is crucial for devising a procedure for extracting HOM power and promoting excellent beam quality. In this work, a method was created to identify and characterize HOMs using a perturbation technique on a copper (Cu) cavity prototype of the BNL3 linac and a double lambda/4 crab cavity. Both analyses and correlation between simulated and measured results are shown. A coaxial to dual-ridge waveguide HOM coupler was designed, constructed and implemented to extract power from HOMs simultaneously making an evanescent fundamental mode for the BNL3 cavity. A full description of the design is given along with a simulated analysis of its performance. Comparison between previous HOM coupler designs as well as correspondence between simulation and measurement is also given. |
