RF and Mechanical Design of 647 MHz 5-Cell BNL4 Cavity for eRHIC ERL

A 647 MHz 5-cell BNL4 cavity was designed for high current FFAG lattice ERL for high luminosity eRHIC. The cavity was optimized to be able to propagate all the HOMs out of the cavity for high BBU threshold current and low HOM power (loss factor). eRHIC will collide electron beam for large energy range of proton (40 GeV to 250 GeV), which requires the cavity to be able to tune up to 170 kHz at 2K. This presents a challenge for the mechanical design of the SRF cavity. This paper will present the RF and mechanical design of the 647 MHz 5cell BNL4 cavity. The status of the cavity fabrication and preparation for vertical test will be addressed as well.