Paper | Title | Page |
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MOXA04 | Superconducting Accelerator for ERL Based FEL EUV Light Source at KEK | 13 |
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An energy recovery linac (ERL)-based free electron laser (FEL) is a possible candidate of a tens of kW EUV source and open the era for next generation EUV-lithography. We have designed the 10 mA class ERL-based EUV-FEL source to generate more than 10 kW power. One of the key technologies is CW superconducting cavities to realize the energy recovery of high beam current of more than 10 mA by suppressing HOMs and high gradient acceleration of higher than 12 MV/m. This CW superconducting cavity had been developed through the construction of the Compact ERL facility in KEK and it successfully achieved the energy recovery of 1 mA CW beam until now. In this talk, first we express our design strategies of SRF cavities of the main linac of ERL-EUV light sources not only to suppress the HOMs but also to overcome the field emission problem by modifying the main linac cavity of Compact ERL more sophisticatedly. Next we show the recent development works for ERL-EUV superconducting cavity about HOM damper, cryomodule, and its clean string-assembly work by using horizontal test stand. | ||
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Slides MOXA04 [5.938 MB] | |
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-MOXA04 | |
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TUXBA04 |
A Unified Theory of Surface Resistance and the Residual Resistance of SRF Cavities at Low Temperatures | |
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The Mattis-Bardeen (MB) theory has been widely used for the calculation of the surface resistance of superconductors at weak RF fields. It is well known that the observed surface resistance decreases exponentially as the temperature decreases but tends to a constant residual resistance which is not described by the MB theory. Using the quasiclassical formalism of the microscopic BCS theory, we have developed a unified theory of the surface resistance which, in addition to the MB contribution, includes the residual resistance. Based on this theory, possible materials treatments to reduce the surface resistance are discussed. | ||
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Slides TUXBA04 [2.207 MB] | |
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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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TUPB028 | Improvement of Magnetic Condition for KEK-STF Vertical Test Facility Toward High-Q Study | 444 |
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Improvement of unloaded Q-values of SRF cavities are important to reduce surface loss of cavity and heat loads of He refrigerators. R&D activities have been developed worldwide. We also started work toward high-Q, but soon realized that magnetic condition of KEK-STF vertical test facility was not good enough to carry out high-Q measurements. First, magnetized components were searched. Shafts to move variable coupler were found to be most magnetized one and exceed more than 1 Gauss. Magnetized components were exchanged to non-magnetized one. In order to further reduce remnant magnetic field, a solenoid coil was prepared and used to cancel it. To suppress flux trapping, a heater was located around an upper beampipe of cavity and made thermal gradient. Owing to these efforts, Q-value of more than 1x1011 can be measured with a condition of residual resistance of ~3 nΩ. Clear flux expulsion signal can be also observed. In this presentation, we report about efforts to reduce ambient magnetic field and to realize high-Q measurements. Results of vertical tests, including flux expulsion measurements, are also presented. | ||
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Poster TUPB028 [1.961 MB] | |
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB028 | |
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THYA02 | Achievement of Stable Pulsed Operation at 36 MV/m in STF-2 Cryomodule at KEK | 722 |
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In the Superconducting RF Test Facility (STF) in KEK, the cooldown test for the STF-2 cryomdoule with 12 cavities has been done totally three times since 2014. In 2016, the 3rd cooldown test for the STF-2 cryomodule including the capture cryomodule with 2 cavities was successfully carried out. The main achievement is the vector-sum operation with 8 cavities at average accelerating gradient of 31 MV/m as the ILC specification (2 of 8 cavities achieved 36 MV/m with piezo compensation), and the others are the measurement for Lorenz Force Detuning (LFD) and unloaded Q value, and Low Level RF (LLRF) study, etc. In this paper, the result for the STF-2 cryomodule in three cooldown tests will be presented in detail. | ||
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Slides THYA02 [4.042 MB] | |
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THYA02 | |
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THPB021 | Trial of Nitrogen Infusion and Nitrogen Doping by Using J-PARC Furnace | 775 |
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KEK has been carrying out SRF cavity developments toward higher Q-values and higher accelerating gradients. In the past nitrogen-doping was tested using the KEK furnaces, but it did not succeed. This time nitrogen infusion and nitrogen doping are tested using the J-PARC's furnace, which has an oil-free pumping system and is mainly pumped by a 10000 L/s cryopump and three 3000 L/s turbo pumps. Nitrogen pressure is controlled by a variable leak valve and an additional turbo pump. To avoid performance degradation during heat treatment, flanges of cavities are covered by Nb caps and foils. Nitrogen infusion at 120 degrees was applied to a single cell cavity and cavity performance was measured by vertical tests after HPR and assembly. Nitrogen doping at 800 degrees is also applied to another single cell cavity. After applying EP and HPR, vertical tests were carried out. Nb samples were also installed into the furnace during heat treatment. Surfaces are analyzed by SIMS and XPS. In this presentation, we report procedure of nitrogen infusion and doping, vertical test results and results of surface analysis. | ||
DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-THPB021 | |
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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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