rf losses in a high gradient cryogenic copper cavity

The development of high brightness electron sources can enable an increase in performance and reduction in size of extreme X-ray sources such as free electron lasers (FELs). A promising path to high brightness is through larger electric fields in radio-frequency (rf) photoinjectors. Recent experimen...

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Bibliographic Details
Main Authors: A. D. Cahill, J. B. Rosenzweig, V. A. Dolgashev, Z. Li, S. G. Tantawi, S. Weathersby
Format: Article
Language:English
Published: American Physical Society 2018-06-01
Series:Physical Review Accelerators and Beams
Online Access:http://doi.org/10.1103/PhysRevAccelBeams.21.061301
Description
Summary:The development of high brightness electron sources can enable an increase in performance and reduction in size of extreme X-ray sources such as free electron lasers (FELs). A promising path to high brightness is through larger electric fields in radio-frequency (rf) photoinjectors. Recent experiments with 11.4 GHz copper accelerating cavities at cryogenic temperatures have demonstrated 500  MV/m surface electric fields with low rf breakdown rates. However, when the surface electric fields are larger than 300  MV/m, the measured cavity quality factor, Q_{0}, decreases during the input rf pulse by up to 30%, recovering before the next rf pulse. In this paper, we present an experimental study of the rf losses, manifested as degradation of Q_{0}, in a copper cavity operated at cryogenic temperatures and high gradients. The experimental conditions range from temperatures of 10–77 K and rf pulse lengths of 100–800 ns, using surface electric fields up to 400  MV/m. We developed a model for the change in Q_{0} using measured field emission currents and rf signals. We find that the Q_{0} degradation is consistent with the rf power being absorbed by strong field emission currents accelerated inside the cavity.
ISSN:2469-9888