Abstract
In this paper, we discuss error analysis for intrinsic quality factor (Q0) and accelerating gradient (Eacc) measurements in superconducting radio frequency (SRF) resonators. The analysis is applicable for cavity performance tests that are routinely performed at SRF facilities worldwide. We review the sources of uncertainties along with the assumptions on their correlations and present uncertainty calculations with a more complete procedure for treatment of correlations than in previous publications [T. Powers, in Proceedings of the 12th Workshop on RF Superconductivity, SuP02 (Elsevier, 2005), pp. 24-27]. Applying this approach to cavity data collected at Vertical Test Stand facility at Fermilab, we estimated total uncertainty for both Q0 and Eacc to be at the level of approximately 4% for input coupler coupling parameter β1 in the [0.5, 2.5] range. Above 2.5 (below 0.5) Q0 uncertainty increases (decreases) with β1 whereas Eacc uncertainty, in contrast with results in Powers [in Proceedings of the 12th Workshop on RF Superconductivity, SuP02 (Elsevier, 2005), pp. 24-27], is independent of β1. Overall, our estimated Q0 uncertainty is approximately half as large as that in Powers [in Proceedings of the 12th Workshop on RF Superconductivity, SuP02 (Elsevier, 2005), pp. 24-27].
Highlights
Near future linear accelerator projects such as LCLS-II will require minimized power losses in superconducting radio frequency (SRF) cavities in comparison with standard International Linear Collider (ILC) requirements
We describe the error analysis procedure developed for cavity measurements at the Vertical Test Stand (VTS) facility for SRF cavities at Fermilab
For a more accurate uncertainty estimate for a given VTS measurement, the procedure described in this paper should be applied
Summary
Near future linear accelerator projects such as LCLS-II will require minimized power losses in superconducting radio frequency (SRF) cavities in comparison with standard International Linear Collider (ILC) requirements. Due to increased demand for improving intrinsic quality factor (Q0), importance of accurate cavity characterization, including measurement error analysis, increases. As new recipes for niobium surface treatment are invented, good error analysis is needed to establish the significance of Q0 improvement achieved with a new recipe. Other topics of SRF R&D where good knowledge of Q0 precision is critical, include, but are not limited to, studies of different cool-down rates, cavity material grain structure, and effects of thermal treatment.. We describe the error analysis procedure developed for cavity measurements at the Vertical Test Stand (VTS) facility for SRF cavities at Fermilab. This procedure can be adapted to similar measurements at other facilities
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