A Proof-of-Principle Demonstration of 805 MHz High Gradient SRF Cavities

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A Proof-of-Principle Demonstration of 805 MHz High Gradient SRF Cavities Abstract An accelerating gradient of 50 MV/m at an unloaded quality factor (Q0) of 1.4 x 1010 was achieved with a single-cell 805 MHz superconducting radio-frequency (SRF) cavity. This accelerating gradient is more than twice as high as the previous maximum gradient at 805 MHz, and the result demonstrates that 805 MHz cavities, which have a larger beam aperture of 10 cm than 6-7 cm for 1.3 GHz high-gradient cavities, can be used, in principle, as high-gradient cavities for various purposes, especially suited for protons, light ions and other machines that require lower beam impedances due to a larger beam aperture of 10 cm compared to 6-7 cm with 1.3 GHz high-gradient cavities. One remarkable fact is that this cavity was only treated with a usual buffered chemical polishing of ~150 microns and an ultra-high vacuum baking at 115-130 ˚C for 48 hours, and it did not have without high temperature treatment except for a vacuum baking at 115-130 ˚C for 48 hours, and without or any costly electro-polishing, that which has been required for 1.3 GHz cavities to get to very high gradients. Text SRF cavities have been used successfully for particle accelerators since 1970s [1]. A large fraction of them are is made of bulk niobium (Nb) due to the fact that it niobium has the highest superconducting transition temperature of ~9.2 K as a single metalamong pure metals. The benefits of SRF cavities compared to normal conducting structures are 1) lower losses due to the intrinsic nature of superconductivity, 2) they can run at higher gradients forin long pulses orand CW operations, and 3) lower beam impedances due to larger beam apertures. However, Nb SRF cavities ... ... middle of paper ... ...ies Tests of High-Gradient Single-Cell Superconducting Cavity for the Establishment of KEK Recipe,” Proc. EPAC’06, p. 756. [4] R.L. Geng et al., “Latest Results of ILC High-Gradient R&D 9-cell Cavities at JLAB,” Proc. SRF2007, p. 525. [5] H. Padamsee, “Americas Regional Report,” TTC meeting, FNAL, 23-26 April 2007. https://indico.desy.de/getFile.py/access?contribId=4&resId=0&materialId=slides&confId=200 [6] J. Sekutowicz, “Low Loss ILC Cavity,” SLAC Seminar, 25 January 2005. http://www.slac.stanford.edu/grp/ara/structures_meeting/JSekutowicz.pdf [7] F. Furuta et al., “Experimental Comaprison at KEK of High Gradient Performacne of Different Cell Superconducting Cavity Designs,” Proc. EPAC’06, p. 750. [8] V. Shemelin, private communication. [9] T. Tajima et al., “SRF Cavity High-Gradient Study at 805 MHz for Proton and Other Applications,” Proc. PAC’09.

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