Paper | Title | Page |
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TUYBA01 | Progress on Characterization and Optimization of Multilayers | 368 |
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Multilayers MgO/NbN/MgO/Nb with several thicknesses are being tested by local magnetometry, Scanning tunneling and various standard structural techniques experiment providing usefull information to compare experiments and recent theoretical advances proposed by A. Gurevich or T. Kubo. | ||
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Slides TUYBA01 [5.819 MB] | |
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUYBA01 | |
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TUPB073 | Vertical Electro-polishing Collaboration Between Cornell, KEK, and Marui Galvanizing Co. Ltd | 563 |
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Cornell's SRF group, KEK, and Marui Galvanizing Co. Ltd (MGI) have collaborated since 2014 on Vertical Electro-Polishing (VEP) R&D as a part of a US/Japan Program for Cooperation in High Energy Physics. We have focused on an improvement of removal uniformity during the VEP process. MGI and KEK have developed their original VEP cathode named i-cathode Ninja®, which has four retractable wing-shape parts per cell. Cornell processed one single cell cavity with VEP using this cathode and performed a vertical test. KEK also provided one 9-cell cavity to Cornell. Cornell then performed surface treatments including Cornell VEP and RF test on this 9-cell cavity. The progress by the VEP collaboration and RF test results are presented in this paper. | ||
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB073 | |
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TUPB091 | Study on Vertical Electropolising of 9-cell Niobium Coupon Cavity | 602 |
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Authors report a study on vertical electropolishing (VEP) carried out for a 1.3 GHz 9-cell niobium (Nb) coupon cavity using a unique cathode namely 'Ninja Cathode'. The design of the cathode for VEP of a 9-cell cavity was based on the Ninja cathode used for 1-cell cavity since the 1-cell Ninja cathode was found effective to reduce longitudinal asymmetry in material removal and to obtain a smooth surface of a 1-cell cavity. Moreover, 1-cell Nb cavities after being treated in VEP using the Ninja cathode showed good performance in vertical RF tests. The 9-cell coupon cavity used in this study was designed to have totally nine coupons set on the iris and equator positions of the first, fifth and ninth cells. These three cells contain viewports as well at their upper and lower iris positions. Measurement of currents from the individual coupons and in-situ observation are possible using the cavity to understand EP phenomenon at different locations of the cavity. VEP results, which include removal thicknesses at different positions of the cavity and surface study of the coupons, are discussed. | ||
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB091 | |
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TUPB092 | Analysis of Niobium Surface and Generated Particles in Vertical Electropolishing of Single-cell Coupon Cavity | 607 |
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In our previous studies, we have reported parameter investigation for vertical electropolishing (VEP) of 1-cell niobium (Nb) tesla/ILC type cavities using a Ninja cathode. A 1-cell coupon cavity containing six Nb disk coupons at its different positions was found effective to reduce time and cost to establish an optimized VEP recipe. In this work, we present surface analyses of VEPed Nb coupon surfaces using scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDX) and x-ray photoelectron spectroscopy (XPS). Surfaces contained micro- and nano-sized particles which were found with random distributions and different number densities on the beam pipe and iris coupons. Surfaces of equator coupons were found to have relatively less number of particles or almost clean. To analyze particles, a few particles were picked-up from a coupon surface using a tungsten tip under SEM and analyzed with EDX while the coupon was moved out from the SEM chamber to avoid its effect in EDX spectra. The particles were confirmed as oxygen-rich niobium and contained fluorine and carbon also. XPS analysis of the coupon surfaces was also carried out for further study of surface chemistry. | ||
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB092 | |
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TUPB093 | Nb Single-cell Cavity Vertical Electro-polishing with Ninja Cathode and Evaluation of its Accelerating Gradient | 612 |
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Marui Galvanizing Co. Ltd. has been improving Vertical Electro-Polishing (VEP) technology for Nb superconducting RF cavity in collaboration with KEK. In this collaboration, we developed a unique cathode namely Ninja cathode for VEP treatment of Nb cavities. We have already reported that longitudinal symmetry in niobium removal and surface state of a single cell cavity were improved after VEP using the Ninja cathode. In this article, we report a result of accelerating gradient evaluation for 1.3 GHz single cell RF cavity after VEP with Ninja cathode in collaboration with KEK and CEA Saclay. | ||
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Poster TUPB093 [0.704 MB] | |
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB093 | |
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TUPB097 | R&D of Electro-polishing (EP) Process with HF-free Neutral Electrolyte by Bipolar-pulse (BP) Method | 623 |
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Currently the Electro-Polishing (EP) process of Superconducting Radio-Frequency (SRF) accelerating cavity is performed with the electrolyte that is the mixture of hydrofluoric and sulfuric acids. However, the electrolyte is very dangerous and the environmental load in the disposal process of electrolyte is very heavy. This is the reason why the high cost is necessary in the safe design of facility and the safe operation of process in the conventional EP method. In such situation, considering the reduction of cost and environmental load in the EP process, we performed the R&D of novel EP process with HF-free neutral electrolyte by Bipolar-Pulse (BP) method. In this presentation, we will report the removal rate, surface roughness and the results of surface analysis for the Nb-coupon samples that were processed by the BP-EP with HF-free neutral electrolyte. | ||
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB097 | |
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THPB055 | Plasma-enhanced ALD System for SRF Cavity | 870 |
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Funding: This work was supported by Photon and Quantum Basic Research Coordinated Development Program by MEXT and partly by JST-CREST. A remote PEALD (Plasma-enhanced Atomic Layer Deposition) system which would offer a high conformality and a low deposition temperature has been being developed for deposition of NbN on an SRF cavity. The deposition equipment consists of a deposition chamber, a remote plasma exciter, a precursor supply system, vacuum pumps, a quartz crystal microbalance (QCM) as a film growth rate meter, a detoxifying system and a safety system. An RF frequency of 13.56MHz was used for the inductively coupled plasma exciter of a reactant gas. The whole equipment is in a draft booth for operation safety. For ALD of an SRF cavity, the ALD system allows us to easily replace the deposition chamber with a single cell Nb cavity. The prepared precursors are tris[ethylmethylamido][tert-butylimido] niobium (TBTEMN) and trimethylaluminium (TMA). Ammonia, hydrogen and water are also prepared as reactants. We will report the ALD system design and result of the NbN deposition on sample coupons which are analysed with SEM, EDX and XPS. |
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DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB055 | |
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THPB058 | R&D of Thin Film Coating on Superconductors | 877 |
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Funding: This research is partially supported by Grant-in-Aid for Exploratory Research JSPS KAKENHI Grant Number 26600142, and Photon and Quantum Basic Research Coordinated Development Program from the MEXT. Multilayer thin film coating is a promising technology to enhance performance of superconducting cavities. Until recently, principal parameters to achieve the sufficient performance had not been known, such as the thickness of each layer. We proposed a method to deduce a set of the parameters to exhibit a good performances. In order to verify the scheme, we are trying to make some experiments on the subject at Kyoto. The sample preparation and the test setup for the measurement apparatus will be discussed. |
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DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB058 | |
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THPB077 | Design Study of Mushroom Shaped Cavity for Evaluation of RF Critical Magnetic Field of Thin-film Superconductor | 914 |
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For future accelerator, superconducting RF cavity has high gradient of 45 MV/m or more is demanded. To obtain such a higher gradient, there has been proposed a method of increasing an RF critical magnetic field of the cavity inner surface by coating of multi-layer thin-film superconductor. Their thickness is close to the London penetration depth. By producing a multilayer film structure in cavity inner surface, it is believed to improve the RF critical magnetic field, and to connect directly to high gradient. To demonstrate a creation of a thin film on a surface of Nb samples, an RF cavity with a thin film coated Nb sample is needed to measure the RF critical field of the sample. To adapt it to the cavity, to cool to cryogenic temperature and to establish the sample to supply the RF power, it is necessary to design a cavity to produce a strong RF magnetic field parallel to the surface of the thin film sample. We designed a mushroom shaped cavity made of Nb and input coupler. Resonant frequency is 5.2 GHz by calculation. We calculated the resonant frequency and the field distribution, compared with the measured values for the model cavity. | ||
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB077 | |
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