The Joint Accelerator Conferences Website (JACoW) is an international collaboration that publishes the proceedings of accelerator conferences held around the world.
TY - CPAPER AU - Goryashko, V.A. AU - Dancila, D.S. AU - Gajewski, K.J. AU - Hermansson, L. AU - Li, H. AU - Nicander, H. AU - Ruber, R.J.M.Y. AU - Santiago Kern, R. AU - Teerikoski, S. TI - High-Precision Measurements of the Quality Factor of Superconducting Cavities at the FREIA Laboratory J2 - Proc. of International Conference on RF Superconductivity (SRF2015), Whistler, BC, Canada, Sept. 13-18, 2015 AB - In this paper we propose a high-precision method of measuring Q0 of SRF cavities. A common way to study the performance of an SRF cavity is to build an oscillator around it that is referred to as a self-exciting loop. In the standard approach, by tuning the loop phase for a maximum field level in the cavity and measuring forward and reflected waves, one finds the cavity coupling. Then, performing a time-decay measurement and finding the total quality factor, one gets Q0. However, this approach suffers from a deficiency originating from a single data-point measurement of the reflection coefficient. In our method by varying the loop phase shift, one obtains amplitudes of the reflection coefficient of the cavity as a function of its phases. The complex reflection coefficient describes a perfect circle in polar coordinates. Fitting the overdetermined set of data to that circle allows more accurate calculation of Q0 via the least-squares procedure. The method has been tested at the FREIA Laboratory on two cavities from IPN Orsay: a single spoke and a prototype ESS double spoke. PB - JACoW CY - Geneva, Switzerland SP - 810 EP - 813 KW - cavity KW - coupling KW - impedance KW - network KW - SRF DA - 2015/12 PY - 2015 SN - 978-3-95450-178-6 DO - 10.18429/JACoW-SRF2015-TUPB089 UR - http://srf2015.vrws.de/papers/tupb089.pdf ER -