Xu, W. Ben-Zvi, I. Blaskiewicz, M. Gao, Y. Holmes, D. Kolb, P. McIntyre, G.T. Porqueddu, R. Smith, K.S. Than, R. Willeke, F.J. Xiao, B. P. Xin, T. Xu, C. Zaltsman, A. JACoW Geneva, Switzerland 978-3-95450-191-5 10.18429/JACoW-SRF2017-TUPB002 English 385-388 TUPB002 HOM ion GUI cavity SRF Contribution to a conference proceedings 2018 2018-01 https://doi.org/10.18429/JACoW-SRF2017-TUPB002 http://jacow.org/srf2017/papers/tupb002.pdf ERL-Ring eRHIC aims to build a new high current (50 mA), multi-pass (6 passes) ERL to provide 3-18 GeV electron beams to collide with proton beams from existing RHIC. One critical challenge for eRHIC is to damp HOMs. The average HOM power is up to 8 kW per cavity, and it will get worse when the electron beam spectrum overlaps with cavity HOM spectrum. A novel HOM damping scheme by employing ridge waveguides has been worked out at BNL, which is able to well damp both longitudinal and transversal modes. This paper will describe the design of the HOM damping scheme, including RF design, HOM damping results, progress of prototyping.