We report the results of surface characterizations of niobium (Nb) samples electropolished together with a single cell superconducting radio-frequency accelerator cavity. These witness samples were located in three regions of the cavity, namely at the equator, the iris, and the beam pipe. Auger electron spectroscopy was utilized to probe the chemical composition of the topmost four atomic layers. Scanning electron microscopy with energy dispersive x ray for elemental analysis was used to observe the surface topography and chemical composition at the micrometer scale. A few atomic layers of sulfur (S) were found covering the samples nonuniformly. Niobium oxide granules with a sharp geometry were observed on every sample. Some Nb-O granules appeared to also contain sulfur.
We report on results of a new investigation into the Q 0 degradation phenomenon observed in original CEBAF cavities when assembled into cryomodules. As a result, the RF dissipation losses increased by roughly a factor of two. The origin of the degradation, first observed in 1993, has remained unresolved up to current period, despite much effort. Recently, a new investigation has been launched, in parallel with cryomodule refurbishment. Systematic measurements are conducted with respect to the magnetic shielding effects of the double-layer shields and the magnetic properties of various components within the inner shield. This resulted in the new discovery of strongly magnetized strut springs as a major source of remanent magnetic flux near a cavity inside of all magnetic shielding. New springs with superior magnetic properties have been found, evaluated and implemented. Preservation of Q 0 from vertical testing to cryomodule testing in tunnel at 5 MV/m gradient in the range of 79-88% has been measured. Studies for complete Q 0 preservation and possible Q 0 remediation for those 330 cavities already installed in CEBAF are carried out and preliminary results are also presented.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.