Konomi, T.K. Adolphsen, C. Gatzmaga, S. Hartung, W. Kelly, M.P. Kim, S.H. Lewellen, J.W. Miller, S.J. Morris, D.G. Murcek, P. Petersen, T.B. Saito, K. Smedley, J. Taylor, A.T. Xiang, R. Xiao, L. Xu, T. Yin, Z.Y. JACoW Publishing Geneva, Switzerland 2673-5504 978-3-95450-234-9 10.18429/JACoW-SRF2023-TUPTB069 English 589-592 cathode gun SRF emittance operation Contribution to a conference proceedings 2023 2023-09 https://doi.org/10.18429/JACoW-SRF2023-TUPTB069 https://jacow.org/srf2023/papers/tuptb069.pdf A SRF gun can operate CW with a high gradient and ultra-low vacuum for high-quantum efficiency, low MTE photocathodes, useful features for delivery of high-brightness, high-repetition-rate beams. For these reasons, an SRF gun based photoinjector was chosen for a proposed Low Emittance Injector addition to the LCLS-II-HE facility, which will operate CW with bunch rates up to 1 MHz. For this injector, a prototype 185.7 MHz QWR gun is being developed in a collaborative effort among FRIB, HZDR, ANL and SLAC, with the goal of achieving a photocathode gradient of at least 30 MV/m. The photocathode is held by a coaxial fixture (cathode stalk) for thermal isolation from the cavity body. The system must allow for precise alignment of the photocathode, particle-free photocathode exchange, cryogenic (55-70 K) or warm (273-300 K) photocathode operating temperatures, and DC biasing to inhibit multipacting. A prototype cathode stalk has been built and bench tests are underway to validate the design. Measurements include RF power dissipation, DC bias hold-off, multipacting suppression and heat transfer effectiveness. This paper describes the cathode stalk design and the test results.