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MOPVA116 | Quench Studies in Single-Cell Nb3Sn Cavities Coated Using Vapour Diffusion | 1119 |
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The superconductor Nb3Sn is known to have a superheating field, Hsh, of approximately 400 mT. This critical field represents the ultimate achievable gradient in a superconducting cavity, and is equivalent to an accelerating gradient of 90 MV/m in an ILC single-cell cavity for this value of Hsh. However, the currently best performing Nb3Sn single-cell cavities remain limited to accelerating gradients of 17-18 MV/m, translating to a peak surface magnetic field of approx. 70 mT. In this paper, we consider theoretical models of candidate quench mechanisms, and compare them to experimental data from surface analysis and cavity tests. | ||
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA116 | |
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MOPVA118 | Impact of Trapped Magnetic Flux and Thermal Gradients on the Performance of Nb3Sn Cavities | 1127 |
SUSPSIK103 | use link to see paper's listing under its alternate paper code | |
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Trapped magnetic flux is known to degrade the quality factor of superconducting cavities by increasing the surface losses ascribed to the residual resistance. In Nb3Sn cavities, which consist of a thin layer of Nb3Sn coated on a bulk niobium substrate, the bimetallic interface results in a thermal current being generated in the presence of a thermal gradient, which will in turn generate flux that can be trapped. In this paper we quantify the impact of trapped flux, from either ambient fields or thermal gradients, on the performance of the cavity. We discover that the sensitivity to trapped flux, a measure of the increase in residual resistance as a function of the amount of flux trapped, is a function of the accelerating gradient. A theoretical framework to explain this phenomenon is proposed, and the impact on the requirements for operating a Nb3Sn cavity in a cryomodule are considered. | ||
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-MOPVA118 | |
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TUPVA136 | Using Sloppy Models for Constrained Emittance Minimization at the Cornell Electron Storage Ring (CESR) | 2418 |
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Funding: DOE DE-SC0013571 NSF DGE-1144153 In order to minimize the emittance at the Cornell Electron Storage Ring (CESR), we measure and correct the orbit, dispersion, and transverse coupling of the beam.* However, this method is limited by finite measurement resolution of the dispersion, and so a new procedure must be used to further reduce the emittance due to dispersion. In order to achieve this, we use a method based upon the theory of sloppy models.** We use a model of the accelerator to create the Hessian matrix which encodes the effects of various corrector magnets on the vertical emittance. A singular value decomposition of this matrix yields the magnet combinations which have the greatest effect on the emittance. We can then adjust these magnet ‘‘knobs'' sequentially in order to decrease the dispersion and the emittance. We present here comparisons of the effectiveness of this procedure in both experiment and simulation using a variety of CESR lattices. We also discuss techniques to minimize changes to parameters we have already corrected. * J. Shanks, D.L. Rubin, and D. Sagan, Phys. Rev. ST Accel. Beams 17, 044003 (2014). ** K.S. Brown and J.P. Sethna, Phys. Rev. E 68, 021904 (2003). |
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DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA136 | |
Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |