| Paper | Title | Other Keywords | Page |
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| MOPMA018 | Simulation of Multipacting in SC Low Beta Cavities at FNAL | simulation, cavity, operation, linac | 579 |
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| Proton Improvement Plan-II at Fermilab is a plan for improvements to the accelerator complex aimed at providing a beam power capability of at least 1 MW on target at the initiation of LBNE (Long Base Neutrino Experiment) operations. The central element of the PIP-II is a new 800 MeV superconducting linac, injecting into the existing Booster. Multipacting affects superconducting RF cavities in the entire range from high energy elliptical cavities to coaxial resonators for low-beta applications. This work is focused on multipacting study in the low-beta 325 MHz spoke cavities; namely SSR1 and SSR2, which are especially susceptible to the phenomena. The extensive simulations of multipacting in the cavities with updated material properties and comparison of the results with experimental data helped us to improve overall reliability and accuracy of these simulations. Our practical approach to the simulations is described in details. For SSR2, which has a high multipacting barrier right at the operating power level, some changes of the cavity shape to mitigate this harmful phenomenon are proposed. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPMA018 | ||
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| MOPHA052 | Optimization of ILC Cryomodule Design Using Explosion Welding Technology | cryomodule, cryogenics, neutron, cavity | 913 |
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| Optimization of ILC cryomodule design using explosion welding technology. B.Sabirov, J.Budagov, G.Shirkov - JINR, Dubna, Russia A.Basti, F.Bedeschi, P.Fabbricatore - INFN, Pisa/Genova, Italy A.Bryzgalin, L.Dobrushin, S.Illarionov, E.Pekar - EWI, Kiev, Ukraine JINR activity in the ILC Project is the development, in association with INFN, of techniques to simplify and make cheaper the construction of the ILC cryomodules. In the current ILC TDR design both the helium vessel shell and the connected pipes are made of expensive titanium, one of the few metals that can be welded to niobium by the electron beam technique. We describe the construction and performance of transition elements, obtained by explosion welding, that can couple the niobium cavity with a stainless steel helium vessel. Several designs for these transitions have been produced and studied showing varying levels of reliability. Based on this experience a new design, including a minimal titanium intermediate layer, has been built. Preliminary tests yield impressive results, indicating a very strong resistance of the bon | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPHA052 | ||
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| WEPMA012 | High-Q Cavity Operation: Study on the Thermoelectrically Induced Contribution to RF Surface Resistance | cavity, simulation, shielding, operation | 2771 |
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| We present a study concerning the operation of a superconducting RF cavity (non-doped niobium) in horizontal testing with the focus on understanding the thermoelectrically induced contribution to the surface resistance. Starting in 2009, we suggested a means of reducing the residual resistance by warming up a cavity after initial cooldown to about 20K and cooling it down again. In subsequent studies we used this technique to manipulate the residual resistance by more than a factor of 2. We postulated that thermocurrents during cooldown generate additional trapped magnetic flux that impacts the cavity quality factor. Since several questions remained open, we present here a more extensive study including measurement of two additional passband modes of the 9-cell cavity that confirms the effect. We also discuss simulations that substantiate the claim. While the layout of the cavity LHe tank system is cylindrically symmetric, we show that the temperature dependence of the material parameters result in a non-symmetric current distribution. Hence a significant amount of magnetic flux can be generated at the RF surface resulting in an increased surface resistance. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMA012 | ||
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| WEPMA037 | Manufacturing and First Test Results of Euclid SRF Conical Half-wave Resonator | cavity, vacuum, SRF, cryogenics | 2841 |
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Funding: This Work is supported by the DOE SBIR Program, contract # DE-SC0006302. Euclid TechLabs has developed a superconducting conical half-wave resonator (162.5 MHz β=v/c=0.11) for the high-intensity proton accelerator complex proposed at Fermi National Accelerator Laboratory. The main objective of this project is to provide a resonator design with high mechanical stability based on an idea of the balancing cavity frequency shifts caused by external loads. A unique cavity side-tuning option has been successfully implemented. Niowave, Inc. proposed a complete cavity production procedure including preparation of technical drawings, processing steps and resonator high-gradient tests. During manufacturing a series of cavity and helium vessel modifications to simplify their manufacturing were proposed. Following standard buffered chemical polish surface treatment and high-pressure rinse, a vertical test was carried out at Niowave’s facilities. Here we present the status of the project and the first high-gradient results. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMA037 | ||
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| WEPMA048 | Development for Mass Production of Superconducting Cavity by MHI | cavity, cryomodule, superconducting-RF, linac | 2876 |
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| Mitsubishi Heavy Industries (MHI) have developed manufacturing process of superconducting cavitis for a long time. In this presentation, recent progress will be reported. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPMA048 | ||
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| WEPHA021 | Status of HIE-ISOLDE SC Linac Upgrade | cavity, cryomodule, linac, vacuum | 3151 |
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| The HIE-ISOLDE upgrade project at CERN aims at increasing the energy of radioactive beams from 3MeV/u up to 10 MeV/u with mass-to-charge ratio in the range 2.5-4.5. The objective is obtained by replacing part of the existing normal conducting linac with superconducting Nb/Cu cavities. The new accelerator requires the production of 32 superconducting cavities in three phases: 10 high-beta cavities for phase 1 (2016), 10 high-beta cavities for phase 2 (2017) and possibly 12 low-beta cavities for phase 3 (2020). Half of the phase 1 production is completed with 5 quarter-wave superconducting cavities ready to be installed in the first cryomodule. The status of the cavity production and the RF performance are presented. The optimal linac working configuration to minimize cryogenic load and maximize accelerating gradient is discussed. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA021 | ||
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| WEPHA022 | Characterization of Nb Coating in HIE-ISOLDE QWR Superconducting Accelerating Cavities by means of SEM-FIB and TEM | cavity, interface, ion, electron | 3155 |
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| The Quarter Wave Resonators (QWR) high-β cavities (0.3m diameter and 0.9m height) are made from OFE 3D-forged copper and are coated by DC-bias diode sputtering with a thin superconducting layer of niobium. The Nb film thickness, morphology, purity and quality are critical parameters for RF performances of the cavity. They have been investigated in a detailed material study. The coating structure at different positions along a test cavity was observed by cross-section imaging using SEM-FIB instrument. The samples from the top of the cavity showed presence of unexpected porosities, whose volume was investigated using FIB tomography. TEM lamella was prepared for two samples (top part and inner conductor of the cavity) to study in detail the grain orientation in the coating, its chemical composition and structure. The 14-layer structure in thick coating was indeed evidenced by the TEM analysis. Chemical mapping revealed the presence of a few nm in size copper precipitates close to the Nb/Cu interface and a passivating oxide layer of 10 nm thickness on top of the coating and around porosities. However no impurities or interface layer along the coating profile were present. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA022 | ||
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| WEPHA052 | Test Cavity and Cryostat for SRF Thin Film Evaluation | cavity, vacuum, SRF, cryogenics | 3232 |
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| In developing superconducting coatings for SRF cavities, the coated samples are tested using various techniques such as resistance measurements, AC and DC magnetometry which provide information about the superconducting properties of the films such as RRR, Hc1, Hc2 and vortex dynamics. However, these results do not allow the prediction of the superconducting properties at RF frequencies. A dedicated RF cavity was designed to evaluate surface resistive losses on a flat sample. The cavity contains two parts: a half-elliptical cell made of bulk Nb and a flat Nb disc. The two parts can be thermally and electrically isolated via a vacuum gap, whereas the electromagnetic fields are constrained through the use of RF chokes. Both parts are conduction cooled hence the system is cryogen free. The flat disk can be replaced with a sample, such as a Cu disc coated with Nb film. The RF test provide the cavity Q-factor and thermometrical measurements of the losses on the sample. The design advantages are that the sample disc can be easily installed and replaced; installing a new sample requires no brazing/welding/vacuum or RF seal, so the sample preparation is simple and inexpensive. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA052 | ||
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| WEPHA058 | Superconducting Coatings Synthesized by CVD/PECVD for SRF Cavities | superconductivity, SRF, plasma, accelerating-gradient | 3246 |
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Funding: STFC Bulk niobium cavities are widely employed in particle accelerators to create high accelerating gradient despite their high material and operation cost. In order to reduce this cost, thin layer of niobium are deposited on a copper cavity, which has lower material cost with higher availability and more importantly higher thermal conductivity. The coating of superconducting cavities currently is synthesized by physical vapour deposition (PVD) method which suffers from lack of conformity. By using chemical vapour deposition (CVD) and plasma enhanced chemical vapour deposition (PECVD) it is possible to deposit thin Nb layers uniformly with density very close to bulk material. This project explores the use of PECVD / CVD techniques to deposit metallic niobium on copper using NbCl5 as precursor and hydrogen as a coreagent. The samples obtained were then characterized via SEM, TEM, SAD, XRD, XPS, and EDX as well as assessing their superconductivity characteristics (RRR and Tc) All the samples deposited are superconductive and polycrystalline; the sample obtained with CVD measured RRR=31 and Tc=7.9 K, while the sample obtained with PECVD exhibited RRR=9 and Tc= 9.4 K. In both cases the films grew in a (100) preferred orientation. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA058 | ||
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| WEPTY009 | Preservation of Quality Factor of Half Wave Resonator during Quenching in the Presence of Solenoid Field | solenoid, cavity, cryomodule, dipole | 3270 |
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Funding: This work was supported by the U.S. Department of energy, Offices of High-Energy Physics and Nuclear Physics, under Contract No. DE-AC02-76-CH03000 and DE-AC02-06CH11357. The Proton Improvement Plan II at FNAL relies upon a 162.5 MHz superconducting half-wave resonator cryomodule to accelerate H− beams from 2.1 to 10 MeV. This cryomodule contains 8 resonators with 8 superconducting solenoid magnets interspersed between them. X-Y steering coils are integrated with a package of the superconducting solenoid magnets. The center of the solenoids is located within ~50 cm of the high surface magnetic field of the half-wave resonators and in this study we assess whether or not magnetic flux generated by this magnet is trapped into the half-wave resonators niobium surface and increases the RF losses to liquid helium. To test this we assembled a solenoid with a 162.5 MHz half-wave resonator spaced as they will be in the cryomodule. We measured the quality factor of the cavity before and after the cavity quenched as a function of field level in the coils. No measurable change in the quality factor was observed. In this paper, we will present details of the measurements and discuss the magnetic field map. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY009 | ||
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| WEPTY010 | Electropolishing for Low-Beta and Quasi-Waveguide SRF Cavities | cavity, cathode, SRF, controls | 3273 |
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| Argonne National Laboratory (ANL) has extended high quality electropolishing techniques based on those developed for the International Linear Collider to several more complex superconducting RF cavities. These include the co-axial TEM-mode quarter-wave and half-wave cavities as well as a 2.8 GHz quasi-waveguide structure intended for beam bunch rotation. This system is an improved version of the one developed for 1.3 GHz 9-cell cavities and includes easy provision for direct water cooling using the helium jacket. The performance of these SRF cavities both in terms of RF fields and losses equals or exceeds that of most 9-cell elliptical cavities built and tested today. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY010 | ||
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| WEPTY018 | Analysis of a Quasi-waveguide Multicell Resonator for SPX | cavity, wakefield, resonance, higher-order-mode | 3299 |
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| A compact deflecting cavity is needed for the Short Pulse X-rays (SPX) at the Advanced Photon Source (APS) of Argonne national laboratory. The deflecting cavity has to quite efficient providing a 2 MV kick voltage and satisfying stringent requirements on aperture size and total cavity length. Meanwhile, the cavity should allow operation up to 100 mT peak surface magnetic field before quenching. In this paper, we report on the latest analysis carried out on the cavity structure to investigate frequency sensitivity to pressure fluctuations, frequency sensitivity to tuning forces, modal frequency, and wakefield losses. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY018 | ||
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| WEPTY021 | Origin of Trapped Flux Caused by Quench in Superconducting Niobium Cavities | cavity, superconductivity, cryogenics, cryomodule | 3309 |
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Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. In this study we prove that the mechanism at the basis of quality factor degradation due to quench involves the entrapment of ambient magnetic field. The cavity quench in the absence of magnetic field does not introduce any extra losses, and a clear trend between the external field and the extra losses introduced by the quench was observed. It is demonstrated that the quality factor can be totally recovered by quenching in zero applied magnetic field. A dependence of the amount of quality factor degradation on the orientation of the magnetic field with respect to the cavity was also found. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY021 | ||
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| WEPTY022 | Modifications of Superconducting Properties of Niobium Caused by Nitrogen Doping Recipes for High Q Cavities | SRF, cavity, superconductivity, vacuum | 3312 |
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Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. Discovery at Fermilab of a drastic effect of nitrogen doping leading to unprecedented high Q values in niobium cavities * motivated a strong interest in revealing the physics underlying the effect. In this contribution we present new results obtained by DC magnetometry, AC susceptibility, resistivity and thermal properties measurements on nitrogen doped samples prepared by different recipes/doping levels, which shed light on the possible origin of the effect. * A. Grassellino et al, 2013 Supercond. Sci. Technol. 26 102001 |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY022 | ||
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| WEPTY031 | Estimation of Cryogenic Heat Loads in Cryomodule due to Thermal Radiation | radiation, cryomodule, cavity, cryogenics | 3338 |
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| Cryogenic system is one of major cost drivers in high intensity superconducting (SC) continuous wave (CW) accelerators. Thermal radiations coming through the warm-ends of cryomodule and room temperature parts of the power coupler result in additional cryogenic heat loads. Excessive heat load in 2K environment may degrade overall performance of the cavity. In this paper we present studies performed to estimate additional heat load at 2K due to thermal radiation in 650 MHz cavity cryomodule in high energy section of PIP-II SC linac. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY031 | ||
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| WEPTY034 | T-map Studies on Gradient-limiting Mechanism in Nitrogen Doped Cavities | cavity, superconductivity, factory, SRF | 3348 |
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Funding: Operated by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. Nitrogen doping * results in ultra-high quality factors in SRF niobium cavities but currently achievable gradients in doped cavities are, on average, somewhat lower than in EP/120C baked cavities. The origin of this difference is explored in the reported work by detailed temperature mapping studies on several single cell nitrogen doped cavities. * A. Grassellino et al, 2013 Supercond. Sci. Technol. 26 102001 |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY034 | ||
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| WEPTY067 | Thermal and Mechanical Analysis of a Waveguide to Coax Symmetric Coupler for Superconducting Cavities | electron, simulation, cavity, dipole | 3434 |
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| As kicks from fundamental power couplers become a concern for low emittance future accelerators, a design for a symmetric coupler for superconducting accelerating cavities has been started. In this coupler, a rectangular waveguide transforms into a coaxial line inside the beam pipe to feed the cavity. So far the RF design revealed an extremely low transversal kick but concerns about cooling and the thermal stability of the coaxial transition line remained. Our contribution will address this. We will calculate heating, heat transfer and thermal stability of this coupler and evaluate the risk of quenching due to particle losses on the coupler. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY067 | ||
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| WEPTY068 | Asymmetric Thermo-currents Diminishing SRF Cavity Performance | cavity, simulation, SRF, superconducting-cavity | 3437 |
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| Over the past years it became evident that the quality factor of a superconducting cavity is not only determined by its surface preparation procedure, but is also influenced by the way the cavity is cooled down. In this paper we will present results from numerical field calculations of magnetic fields produced by thermo-currents, driven by temperature gradients and material transitions. We will show how they can impact the quality factor of a cavity by producing a magnetic field at the RF surface of the cavity. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY068 | ||
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| WEPTY073 | Update on Nitrogen Doping: Quench Studies and Sample Analysis | cavity, vacuum, SRF, radiation | 3450 |
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Funding: U.S. Department of Energy, NSF Recently, nitrogen-doping of niobium has emerged as a promising preparation method for SRF cavities to reach higher intrinsic quality factors than can be reached with typical cavity preparation. Nitrogen-doped cavities prepared at Cornell have shown quality factors higher than 4x1010 at 2.0 K and 16 MV/m. While Q results have been very exciting, a reduced quench field currently limits nitrogen-doped cavities with quench typically occurring between 15 and 25 MV/m. Here we report on recent results from Cornell on single-cell and 9-cell cavities, focusing on new preparations and maximum and critical fields. First we discuss results from over-doping niobium with nitrgoen, baking nitrogen-doped cavities at 120C, and doping with Argon. For a subset of these cavities we show results from quench studies that have been completed using temperature mapping. Finally, we present the first measurements of the higher critical field, Hc2, for nitrogen-doped niobium samples. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY073 | ||
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| WEPTY074 | Recent Studies on the Current Limitations of State-of-the-Art Nb3Sn Cavities | cavity, cryomodule, controls, accelerating-gradient | 3454 |
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Funding: NSF PHY-1305500 PHY-14116318 DOE ER41802 Recent advances in the study of Nb3Sn at Cornell University have yielded single-cell cavities that show excellent performance without the limiting Q-slope seen in previous work. This performance has been shown to be repeatable across multiple cavities. However, they are still limited by a quench field of approximately 16 MV/m, as well as residual resistance. In this work we present results quantifying the impact of ambient magnetic fields on Nb3Sn cavities, as well as discuss the impact of cavity cooldown procedures on cavity performance. Finally, we will briefly discuss XRD results that shed light on the composition of the Nb3Sn layer and how this relates to the current limits of these cavities. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY074 | ||
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| WEPTY075 | Hc2 Measurements of Nb3Sn and Nitrogen-doped Niobium using Physical Property Measurement System | SRF, controls, superconductivity, radio-frequency | 3458 |
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| The measurement of the upper critical field of a type-2 superconductor, Hc2, is an important step in determining its superconducting properties, and therefore its suitability as a material in SRF cavities. However, measuring Hc2 directly can be challenging, as performing electrical measurements causes changes in the very properties one seeks to measure. We present a method for extracting Hc2 from resistivity measurements made near the transition temperature for varied applied fields and excitation currents. We also present results of these measurements made on Nb3Sn and nitrogen-doped niobium. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY075 | ||
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| WEPTY076 | RF Performance Studies of Thin-Film Superconductors Using a Sample Host Cavity | cavity, SRF, operation, background | 3462 |
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| Thin-film superconductors have the potential for reduced cost and for improved SRF performance over traditional bulk niobium superconducting cavities. Materials such as Nb3Sn, multilayer NbN/MgO, and thin-film Nb are currently under investigation for cost reduction or possible improvements in RF losses and accelerating gradients. Due to the complex geometries of traditional RF cavities, it is preferable to use a sample host cavity to study flat samples of the novel materials. The Cornell sample host cavity has been commissioned and has now reached peak magnetic surface fields of 100 mT. We present updates on the recent performance of the cavity. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY076 | ||
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| WEPTY077 | On Quench Propagation, Quench Detection, and Second Sound in SRF Cavities | cavity, simulation, SRF, radio-frequency | 3464 |
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| The detection of a second sound wave, excited by a quench, has become a valuable tool in diagnosing hot spots and performance limitations of superconducting cavities. Several years ago, Cornell developed an oscillating super-leak transducer (OST) for these waves that nowadays are used world-wide. In a usual set-up, several OSTs surround the cavity, and the quench location is determined by triangulation of the different OST signals. Convenient as the method is there is a small remaining mystery: taking the well-known velocity of the second sound wave, the quench seems to come from a place slightly above the cavity’s outer surface. We will present a model based on numerical quench propagation simulations and analytic geometrical calculations that help explain the discrepancy. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY077 | ||
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| WEPTY078 | High Q0 at Medium Fields in Nb3Sn SRF Cavities at 4.2 K | cavity, cryogenics, SRF, operation | 3467 |
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| Nb3Sn has proven itself to be a very promising alternative SRF material. With twice the critical temperature of niobium cavities, 1.3 GHz Nb3Sn cavities can achieve quality factors on the order of 1010 even at 4.2 K, significantly reducing cryogenic infrastructure and operational costs. In addition, its large predicted superheating field may allow for maximum accelerating gradients up to twice that of niobium for high energy applications. In this work, we report on new cavity results from the Cornell Nb3Sn SRF program demonstrating a significant improvement in the maximum field achieved with high Q0 in a Nb3Sn cavity. At 4.2 K, accelerating gradients above 16 MV/m were obtained with Q0 of 8x109, showing the potential of this material for future applications. In addition to this result, current limitations are discussed. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPTY078 | ||
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| WEPWI009 | Nitrogen Doping Study in Ingot Niobium Cavities | cavity, SRF, accelerating-gradient, radio-frequency | 3506 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 Thermal diffusion of nitrogen in superconducting radio frequency cavities at temperatures around 800C has resulted in the increase in quality factor with a low-field Q-rise. However, the maximum accelerating gradients of these doped cavities often reduces below the values achieved by standard treatments. In this contribution, we present the results of the nitrogen diffusion into ingot niobium cavities subjected to successive material removal from the inner cavity surface by electropolishing in an effort to explore the underlying cause for the gradient degradation. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI009 | ||
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| WEPWI010 | Results from the First Single Cell Nb3Sn Cavity Coatings at JLab | cavity, network, accelerating-gradient, resonance | 3509 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Nb3Sn is a promising superconducting material for SRF applications and has the potential to exceed the limitations of niobium. We have used the recently commissioned Nb3Sn coating system to investigate Nb3Sn coatings on several single cell cavities by applying the same coating procedure on several different single cells with different history and pre-coating surface preparation. We report on our findings with four 1.5 GHz CEBAF-shape single cell and one 1.3 GHz ILC-shape single cavities that were coated, inspected, and tested. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI010 | ||
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| WEPWI011 | Commissioning Results of Nb3Sn Cavity Vapor Diffusion Deposition System at JLab | cavity, SRF, vacuum, network | 3512 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Nb3Sn as a BCS superconductors with a superconducting critical temperature higher than that of niobium offers potential benefit in lower surface resistance at the same temperature and frequency for SRF cavities. A Nb3Sn vapor diffusion deposition system was built and commissioned at Jefferson Lab. As the part of the commissioning a single cell 1.5 GHz CEBAF-shaped cavity was coated in the built system. The cavity exhibited the superconducting transition at about 17.9 K. The low field quality factor was about 5x109 at 4 K and 7x109 at 2 K dropping with field to about 109 at both temperatures at about 8 MV/m. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI011 | ||
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| WEPWI013 | New Results of Development on High Efficiency High Gradient Superconducting RF Cavities | cavity, SRF, linac, photon | 3518 |
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| We report on the latest results of development on high efficiency high gradient superconducting radio frequency (SRF) cavities. Several 1-cell cavities made of large-grain niobium (Nb) were built, processed and tested. Two of these cavities are of the Low Surface Field (LSF) shape. Series of tests were carried out following controlled thermal cycling. Experiments toward zero-field cooling were carried out. The best experimentally achieved results are Eacc = 41 MV/m at Q0 = 6.5×1010 at 1.4 K by a 1-cell 1.3 GHz large-grain Nb TTF shape cavity and Eacc = 49 MV/m at Q0 = 1.5×1010 at 1.8 K by a 1-cell 1.5 GHz large-grain Nb CEBAF upgrade low-loss shape cavity. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI013 | ||
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| WEPWI015 | BNL 56 MHz HOM Damper Prototype Fabrication at JLab | cavity, HOM, network, vacuum | 3521 |
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| A prototype Higher-Order Mode (HOM) Damper was fabricated at JLab for the Relativistic Heavy-Ion Collider’s (RHIC) 56 MHz cavity at Brookhaven National Laboratory (BNL). Primarily constructed from high RRR Niobium and Sapphire, the coaxial damper presented significant challenges in electron-beam welding (EBW), brazing and machining via acid etching. The results of the prototype operation brought about changes in the damper design, due to overheating braze alloys and possible multi-pacting. Five production HOM dampers are currently being fabricated at JLab. This paper outlines the challenges faced in the fabrication process, and the solutions put in place. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI015 | ||
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| WEPWI019 | Quench Studies of Six High Temperature Nitrogen Doped 9 Cell Cavities for Use in the LCLS-II Baseline Prototype Cryo-module at Jefferson Laboratory | cavity, SRF, cryomodule, injection | 3528 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Jefferson Lab (JLab) processed six nine-cell cavities as part of a small-scale production for LCLS-II cavity processing development utilizing the promising nitrogen-doping process. [1] Various nitrogen-doping recipes have been scrutinized to optimize process parameters with the aim to guarantee an unloaded quality factor (Q 0) of 2.7·1010 at an accelerating field (Eacc) of 16 MV/m at 2.0 K in the cryomodule. During the R&D phase the characteristic Q0 vs. Eacc performance curve of the cavities has been measured in JLab’s vertical test area at 2 K. The findings showed the characteristic rise of the Q0 with Eacc as expected from nitrogen-doping. Initially, five cavities achieved an average Q0 of 3.3·1010 at the limiting Eacc averaging to 16.8 MV/m, while one cavity experienced an early quench accompanied by an unusual Q 0 vs. Eacc curve. The project accounts for a cavity performance loss from the vertical dewar test (with or without the helium vessel) to the horizontal performance in a cryomodule, such that these results leave no save margin to the cryomodule specification. Consequently, a refinement of the nitrogen-doping has been initiated to guarantee an average quench field above 20 MV/m without impeding the Q 0. This paper covers the refinement work performed for each cavity, which depends on the initial results, as well as a quench analysis carried out before and after the rework during the vertical RF tests as far as applicable. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI019 | ||
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| WEPWI021 | An Analysis of the Temperature and Field Dependence of the RF Surface Resistance of Nitrogen-Doped Niobium SRF Cavities with Respect to Existing Theoretical Models | cavity, SRF, site, superconductivity | 3532 |
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Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177 Recent progress with the reduction of rf surface resistance (Rs) of niobium SRF cavities via the use of high temperature surface doping by nitrogen has opened a new regime for energy efficient accelerator applications. For particular doping conditions one observes dramatic decreases in Rs with increasing surface magnetic fields. The observed variations as a function of temperature may be analyzed in the context of recent theoretical treatments in hopes of gaining insight into the underlying beneficial mechanism of the nitrogen treatment. Systematic data sets of Q0 vs. Eacc vs. temperature acquired during the high Q0 R&D work of the past year will be compared with theoretical model predictions. * * B. P. Xiao et al., Physica C: Superconductivity 490 (0), 26-31 (2013) and A. Gurevich, PRL 113 (8), 087001 (2014) |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI021 | ||
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| WEPWI032 | Mechanical Properties of Niobium Cavities | cavity, SRF, electron, cryogenics | 3554 |
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Funding: This manuscript has been authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177 The mechanical stability of bulk Nb cavity is an important aspect to be considered in relation to cavity material, geometry and treatments. Mechanical properties of Nb are typically obtained from uniaxial tensile tests of small samples. In this contribution we report the results of measurements of the resonant frequency and local strain along the contour of single-cell cavities made of ingot and fine-grain Nb of different purity subjected to increasing uniform differential pressure, up to 6 atm. Measurements have been done on cavities subjected to different heat treatments. Good agreement between finite element analysis simulations and experimental data in the elastic regime was obtained with a single set of values of Young’s modulus and Poisson’s ratio. The experimental results indicate that the yield strength of medium-purity ingot Nb cavities is higher than that of fine-grain, high-purity Nb. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI032 | ||
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| WEPWI038 | Temperature Mapping of Nitrogen-doped Niobium Superconducting Radiofrequency Cavities | cavity, SRF, radio-frequency, cryogenics | 3575 |
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| It was recently shown that diffusing nitrogen on the inner surface of superconducting radiofrequency (SRF) cavities at high temperature can improve the quality factor of the niobium cavity. However, a reduction of the quench field is also typically found. To better understand the location of rf losses and quench, we used a thermometry system to map the temperature of the outer surface of ingot Nb cavities after nitrogen doping and electropolishing. Surface temperature of the cavities was recorded while increasing the rf power and also during the quenching. The results of thermal mapping showed no precursor heating on the cavities and quenching to be ignited near the equator where the surface magnetic field is maximum. Hot-spots at the equator area during multipacting were also detected by thermal mapping. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI038 | ||
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| WEPWI039 | Engineering Study of Crab Cavity HOM Couplers for LHC High Luminosity Upgrade | HOM, cavity, damping, luminosity | 3578 |
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| The LHC is planning to employ crab cavities for the high luminosity upgrade. Old Dominion University and SLAC National Laboratory are developing the crab cavity completed with the HOM damping couplers. The HOM couplers are coaxial type and perform over broad band up to 2 GHz. The amount of extracted power requires active cooling using liquid helium. The electromagnetic study has provided expected power dissipation on the coupler. Correlations between the fabrication tolerance and its damping performance have been studied and the results are providing guidelines on how to manufacture the HOM couplers. This paper summarizes the engineering studies; mechanical strength as a part of pressure system, thermal stability, and fabrication method to ensure the required tolerance. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI039 | ||
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| WEPWI040 | Experiment and Results on Plasma Etching of SRF Cavities | cavity, plasma, SRF, ion | 3581 |
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| The inner surfaces of SRF cavities are currently chemically treated (etched or electro polished) to achieve the state of the art RF performance. We designed an apparatus and developed a method for plasma etching of the inner surface for SRF cavities. The process parameters (pressure, power, gas concentration, diameter and shape of the inner electrode, temperature and positive dc bias at inner electrode) are optimized for cylindrical geometry. The etch rate non-uniformity has been overcome by simultaneous translation of the gas point-of-entry and the inner electrode during the processing. A single cell SRF cavity has been centrifugally barrel polished, chemically etched and RF tested to establish a baseline performance. This cavity is plasma etched and RF tested afterwards. The effect of plasma etching on the RF performance of this cavity will be presented and discussed. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI040 | ||
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| WEPWI046 | Demonstration of Coaxial Coupling Scheme at 26 MV/m for 1.3 GHz TESLA-type SRF Cavities | cavity, coupling, SRF, acceleration | 3594 |
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Funding: Work sponsored by DOE SBIR Grant DE-SC0002479. We will report the first successful rf test of a detachable coaxial coupler by Euclid Techlabs and Fermilab SRF development department. The coaxial coupling method has vast advantages compared with ordinary welded-on couplers. It totally eliminates coupler kicks and it is detachable and easy to clean. We reached 26 MV/m (no hard quench limit) with a quarter-wave detachable coaxial coupler. This is also a demonstration of the highest field gradient ever reached with a superconducting joint. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPWI046 | ||
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| THPF021 | Structural, Mechanical and RF Measurements on the Superconducting 217 MHz CH Cavity for the CW Demonstrator at GSI | cavity, simulation, resonance, operation | 3730 |
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Funding: Work supported by HIM, GSI, BMBF Contr. No. 05P12RFRBL Together with the new horizontal cryomodule and two superconducting (sc) 9.5 T solenoids the sc 217 MHz Crossbar-H-mode (CH) cavity represents the continuous wave (cw) demonstrator and brings sc rf technology to GSI. A reliable operability of the sc CH cavity is one major goal of the demonstrator project. Furthermore, the successful beam operation of the demonstrator will be a milestone on the way to a new sc cw linac at GSI for a competitive production of Super Heavy Elements (SHE) in the future. The production of the cryomodule and the solenoids is almost finished while the cavity has been completed except for the helium vessel. In this paper structural mechanical as well as related rf measurements on the sc 217 MHz CH cavity are presented. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-THPF021 | ||
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| THPF069 | The Early Results of the Vertical Test for β=0.12 HWR at RISP | cavity, coupling, vacuum, cryogenics | 3839 |
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| At RISP, we are planning to perform the vertical test of the β=0.12 half wave resonator. We report our progress on the preparation of the test including the cryogenic system, the RF system, the control and data acquisition system, and the radiation shields. We had the first few occaaisions of the cool down and various measurements at a low gradient. Out preliminary result on the Q0-Eacc excitation curve will be given. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-THPF069 | ||
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