Evidence of increased radio-frequency losses in cavities from the fundamental power coupler cold window

High radio-frequency (rf) losses measured for cavities in original Continuous Electron Beam Accelerator Facility (CEBAF) cryomodules, compared to the single-cavity tests, have been a long-standing issue related their performance. We summarize experimental evidence of increased rf CEBAF arising from fundamental power coupler cold window and waveguide, respectively. Cryogenic tests were done on tested vertical cryostats as well inside cryomodules accelerator tunnel. The metallization assessed by combining numerical results with data obtained an existing cryogenic waveguide resonator setup. showed that can increase cavity heat load at 2.07 K up 86%, depending standing-wave pattern such are reduced if distance between cells is increased.