Lou, W. Hoffstaetter, G.H. JACoW Publishing Geneva, Switzerland 978-3-95450-184-7 10.18429/JACoW-IPAC2018-THPAF022 English 2996-2999 THPAF022 Contribution to a conference proceedings 2018 2018-06 https://doi.org/10.18429/JACoW-IPAC2018-THPAF022 http://jacow.org/ipac2018/papers/thpaf022.pdf Cornell University and Brookhaven National Laboratory are currently designing the Cornell-BNL ERL-FFAG Test Accelerator (CBETA). To be built at Cornell Wilson Lab, CBETA utilizes the existing ERL injector and main linac cryomodule (MLC). As the electron bunches pass through the MLC cavities, higher order modes (HOMs) fields are excited. The recirculating bunches interact with the HOMs, which can give rise to beam-breakup instability (BBU). We would present simulation results on how BBU limits the maximum achievable current, and potential ways to improve the threshold current.