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| WEPMK015 | Optimization of Vertical Electro-Polishing Process: Experiments with Updated Cathode on Single-Cell Cavity and Performance Achieved in Vertical Test | 2662 |
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| Marui Galvanizing Co.Ltd., and CEA have been studying Vertical Electro-Polishing (VEP) on Nb single-cell accelerating superconducting accelerator cavity with the goal of mass-production and cost-reduction, in collaboration with KEK within TYL-FJPPL Particle Physics Laboratory. Marui has invented and patented a rotative cathode called ‘i-Ninja'. The version 5 has been tested for the first time in Europe at CEA Saclay. The four wings of the cathode remove efficiently, bubbles of hydrogen, and the chosen parameters make it possible to achieve better surface and uniform material removal compared to VEP with a fixed cathode. The effect of the temperature of the cavity walls on current oscillations has been precisely studied. Two single-cell cavities have been electro-polished and tested at 2 K in vertical cryostat and the results will be presented. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMK015 | |
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| THPAL015 | Evaluation of superconducting characteristics on the thin-film structure by NbN and Insulator coatings on pure Nb substrate | 3653 |
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Funding: The work is supported by JSPS KAKENHI Grant Numbers JP17H04839, JP26600142 and the Collaborative Research Program of ICR Kyoto University (grant 2016-8, 2017-8, 2017-9). In recent years, it is pointed out that the maximum accelerating gradient of a superconducting RF cavity can be pushed up by coating the inner surface of cavity with a multilayer thin-film structure that consists of alternate insulator and superconductive layers. In this structure, the principal parameter that limits the performance of the cavity is the critical magnetic field or effective Hc1 at which vortices start penetrate into the first superconductor layer. We made a sample that has NbN/SiO2 thin-film structure on pure Nb substrate by DC magnetron sputtering method. In this paper, we will report the measurement results of effective Hc1 of the sample by the third-harmonic voltage method. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL015 | |
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| THPAL029 | Comparison of Horizontal and Vertical Electropolishing Methods using Niobium Single-Cell Coupon Cavity | 3692 |
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| Horizontal electropolishing (HEP) is an established tech-nique for surface treatment of niobium accelerating cavi-ties. Vertical electropolishing (VEP), in which the cavity is electropolished in the vertical posture, is in R&D phase for parameter optimization. We performed HEP and VEP of a niobium single-cell coupon cavity to compare the effect of both the methods on surface state and removal at different positions of the cavity. HEP was performed at STF, KEK with the standard EP parameters. VEP was performed at Marui Galvanizing Company with a cathode called 'Ninja cathode' that can be rotated during the VEP process. The optimized cathode design and VEP parame-ters resulted in symmetric removal as obtained with the HEP technique and yielded a smooth inner surface of the entire cavity | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL029 | |
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| THPAL030 | Vertical Electropolishing of 1.3 GHz Niobium 9-Cell Cavity: Parameter Study and Cavity Performance | 3695 |
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| VEP parameters and process have been already optimized with single-cell 1.3 GHz niobium cavity at Marui Galva-nizing Company working in collaboration with KEK. A unique cathode called 'Ninja cathode' with an optimized shape was applied to single-cell cavities. The cathode was effective to stop the bubble accumulation in the upper half-cell of the cavity and yielded smooth surface and uniform removal in the cell. This work shows parameter study with the Ninja cathode and a 9-cell coupon cavity which contains totally 9 coupons and viewports in the first, fifth, and ninth cells. Effects of temperature and acid flow in the cathode housing were studied using coupon currents and by observing bubbles through the viewports. The adequate parameters found with 9-cell coupon cavity were applied on a 9-cell cavity to be tested in vertical cryostat. The VEP and vertical test results are reported. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL030 | |
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| THPAL031 | Development of a Vertical Electropolishing Facility for Nb 9-Cell Cavity | 3699 |
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| Our Nb accelerating cavity vertical electropolishing (VEP) facility development group which was led by KEK started single-cell VEP facility development from 2014. This is based on horizontal electropolishing (HEP) techniques developed by KEK over 10 years and stainless steel electropolishing techniques developed by Marui over 30 years. We have reported results of Nb cavity VEP with Ninja cathode so far. In order to achieve international linear collider (ILC) construction, it is said that cost reduction and productivity improvement are necessary, however in case of 9-cell cavity, uniform inner surface polishing is difficult, as well known to predecessors. In this article, we will present the first report of VEP facility development from initial transparent plastic mock-up to improvement for Nb 9-cell cavity. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL031 | |
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| THPAL032 | 1.3GHz Nb Single-Cell Cavity Vertical Electropolishing with Ninja Cathode and Results of Vertical Test | 3702 |
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| Marui Galvanizing Co., Ltd. has been developing Nb cavity vertical electropolishing (VEP) technologies in collaboration with KEK. Until now, we reported that inner surface state and removal thickness distribution were improved in VEP with Ninja cathode and coupon cavity. This time, a 1.3GHz Nb single-cell cavity VEP with Ninja cathode was performed in Marui and vertical test was performed in KEK. The inner surface state and removal thickness distribution were satisfactory. And as a result of vertical test, the accelerating gradient of 32MV/m (Q0=8.0E9) was achieved. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL032 | |
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| THPAL105 | Lower Critical Field Measurement System of Thin Film Superconductor | 3882 |
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Funding: The work is supported by Japan Society for the Promotion of Science Grant-in-Aid for Young Scientist (A) No.17H04839. Superconducting thin film is the promising technology to increase the performance of SRF cavities. The lower critical field Hc1, which is one of the important physical parameters characterizing a superconducting material, will be enhanced by coating Nb with thin film superconductor such as NbN. To investigate the performance of thin film, we developed the Hc1 measurement system using the third harmonic response of applied AC magnetic field. The measurement system consists of helium cryostat with two of GM refrigerators, sample Cu stage, solenoid coil Cu mount, solenoid coil, temperature sensors, and liquid helium level meter. AC magnetic field is produced by a coil which is driven by function generator and power amplifier at around 1 kHz. In order to control the temperature of the sample stage and coil mount, the depth of thermal anchors attached to the stage and the mount can be moved by the motor. By this temperature control the sample state can be easily transferred from Meissner state to mixed state. So that the measurement is repeated for various applied magnetic field, and the transition curve can be made. In this report, performance of the measurement system is described. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL105 | |
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| THPML120 | Development of Coating Technique for Superconducting Multilayered Structure | 4954 |
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| In order to increase the maximum acceleration gradient of SRF cavities, S-I-S (superconductor-insulator-superconductor) multilayered structure theory has been proposed. We focused on NbN which has a higher superconducting transition temperature than Nb. Firstly, we researched the optimal deposition condition for N2 gas reactive sputtering of NbN by using in-house inter-back type DC magnetron sputtering equipment. The critical condition for a thin film with strong crystalline orientation of NbN was identified. The superconducting transition temperature of the NbN thin film, which were coated under the best condition, was over 14 K. Secondly, we tried making S-I-S multilayered samples that was composed of NbN/SiO2/Nb substrate. The coating condition for the NbN layer was determined based on the research results in a single layer. The SiO2 layer was deposited with a film thickness of 30 nm that was theoretically expected to be effective as barrier layer. We applied O2 gas reactive AC magnetron sputtering for coating. In this article, the detailed results of the NbN single layer and multilayer film depositions are presented. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML120 | |
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