Khabiboulline, T.N. Awida, M.H. Gonin, I.V. Lunin, A. Solyak, N. Yakovlev, V.P. JACoW Geneva, Switzerland 978-3-95450-180-9 10.18429/JACoW-NAPAC2016-WEPOB27 English 960-963 WEPOB27 ion HOM cavity FEL linac Contribution to a conference proceedings 2017 2017-01 http://dx.doi.org/10.18429/JACoW-NAPAC2016-WEPOB27 https://jacow.org/napac2016/papers/wepob27.pdf A 3.9 GHz 3rd harmonic cavity was developed at FNAL and it is currently used in the FLASH accelerator at DESY in order to improve FEL operation. The European XFEL accelerator in Hamburg also adapted the same cavity design for a pulsed linac operation. The 3rd harmonic cavity for the LCLS-II accelerator at SLAC will operate in a continuous wave (CW) regime. A CW operation and a high average current in the LCLS-II linac result in in-creased heat loads to main and HOM couplers of the cavity. Several cavity design modifications were pro-posed and investigated for improving a cavity perfor-mance in the CW regime. In this paper we present results of the design review for proposed modifications