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TY - CONF AU - Umemori, K. AU - Dohmae, T. AU - Kako, E. AU - Konomi, T. AU - Kubo, T. AU - Masuzawa, M. AU - Okada, T. AU - Park, G.-T. AU - Terashima, A. AU - Tsuchiya, K. AU - Ueki, R. ED - Schaa, Volker RW ED - He, Yuan ED - Li, Lu ED - Zhao, Ning TI - Improvement of Magnetic Condition for KEK-STF Vertical Test Facility Toward High-Q Study J2 - Proc. of SRF2017, Lanzhou, China, July 17-21, 2017 C1 - Lanzhou, China T2 - International Conference on RF Superconductivity T3 - 18 LA - english AB - Improvement of unloaded Q-values of SRF cavities are important to reduce surface loss of cavity and heat loads of He refrigerators. R&D activities have been developed worldwide. We also started work toward high-Q, but soon realized that magnetic condition of KEK-STF vertical test facility was not good enough to carry out high-Q measurements. First, magnetized components were searched. Shafts to move variable coupler were found to be most magnetized one and exceed more than 1 Gauss. Magnetized components were exchanged to non-magnetized one. In order to further reduce remnant magnetic field, a solenoid coil was prepared and used to cancel it. To suppress flux trapping, a heater was located around an upper beampipe of cavity and made thermal gradient. Owing to these efforts, Q-value of more than 1x10¹¹ can be measured with a condition of residual resistance of ~3 nΩ. Clear flux expulsion signal can be also observed. In this presentation, we report about efforts to reduce ambient magnetic field and to realize high-Q measurements. Results of vertical tests, including flux expulsion measurements, are also presented. PB - JACoW CP - Geneva, Switzerland SP - 444 EP - 447 KW - ion KW - cavity KW - solenoid KW - SRF KW - controls DA - 2018/01 PY - 2018 SN - 978-3-95450-191-5 DO - 10.18429/JACoW-SRF2017-TUPB028 UR - http://jacow.org/srf2017/papers/tupb028.pdf ER -