Photoemission Phenomena on CEBAF RF Windows at Cryogenic Temperatures

This paper reports on the photoemission observed during the tests on a single-cell 1500 MHz niobium cavity with a polycrystalline alumina rf interface window operated at 2K. The light emission from the window at 2K was detected using a multi-channel fiber optics/PMT system and recorded with a 100 Ms/sec acquisition system. The spectral composition of two types of discharges has been measured. The results indicate that both broadband and narrow-band emissions are present, depending on the discharge type