Xu, W. Ben-Zvi, I. Gao, Y. Holmes, D. Kolb, P. McIntyre, G.T. Pai, C. Porqueddu, R. Smith, K.S. Than, R. Tuozzolo, J.E. Willeke, F.J. Zaltsman, A. JACoW Geneva, Switzerland 978-3-95450-191-5 10.18429/JACoW-SRF2017-MOPB009 English 64-66 MOPB009 cavity ion SRF HOM linac Contribution to a conference proceedings 2018 2018-01 https://doi.org/10.18429/JACoW-SRF2017-MOPB009 http://jacow.org/srf2017/papers/mopb009.pdf eRHIC ERL SRF requires 160 5-cell 650 MHz SRF cavities. The 650 MHz cavity has been designed and two prototypes have been fabricated, one Cu cavity for HOM study and one Nb cavity for cavity performance study. This paper will describe cavity design and the progress of prototyping.