Paper | Title | Page |
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SUPFDV015 | Preliminary Results from Magnetic Field Scanning System for a Single-Cell Niobium Cavity | 96 |
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One of the building blocks of modern particle accelerators is superconducting radiofrequency (SRF) cavities. Niobium is the material of choice to build such cavities, which operate at liquid helium temperature (2 - 4 K) and have some of the highest quality factors found in Nature. There are several sources of residual losses, one of them is trapped magnetic flux, which limits the quality factor in SRF cavities. The flux trapping mechanism depends on different niobium surface preparations and cool-down conditions. Suitable diagnostic tools are not yet available to study the effects of such conditions on magnetic flux trapping. A magnetic field scanning system (MFSS) for SRF cavities using Hall probes and Fluxgate magnetometer has been designed, built, and is commissioned to measure the local magnetic field trapped in 1.3 GHz single-cell SRF cavities at 4 K. In this contribution, we will present the preliminary results from MFSS for a single cell niobium cavity. | ||
DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-SUPFDV015 | |
About • | Received ※ 21 June 2021 — Revised ※ 13 August 2021 — Accepted ※ 08 November 2021 — Issue date ※ 27 April 2022 | |
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SUPTEV010 | Electrical and Thermal Properties of Cold-Sprayed Bulk Copper and Copper-Tungsten Samples at Cryogenic Temperatures | 142 |
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Funding: Work supported by the U.S. Department of Energy, Office of Science, SBIR grant DE-SC00195589 The development of high thermal conductivity coatings with pure copper or copper-tungsten alloy could be beneficial to improve the heat transfer of bulk Nb cavities for conduction cooling applications and to increase the stiffness of bulk Nb cavities cooled by liquid helium. Cold-spray is an additive manufacturing technique suitable to grow thick coatings of either Cu or CuW on a Nb substrate. Bulk (~5 mm thick) coatings of Cu and CuW were deposited on standard 3 mm thick, high-purity Nb samples and smaller samples with 2 mm x 2 mm cross section were cut for measuring the thermal conductivity and the residual resistivity ratio. The samples were subjected to annealing at different temperatures and a maximum RRR of ~130 and ~40 were measured for the Cu samples and CuW samples, respectively. |
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DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-SUPTEV010 | |
About • | Received ※ 21 June 2021 — Revised ※ 13 August 2021 — Accepted ※ 15 November 2021 — Issue date ※ 21 March 2022 | |
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MOPCAV001 | Cavity Production and Testing of the First C75 Cryomodule for CEBAF | 250 |
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Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. The CEBAF cryomodule rework program was updated over the last few years to increase the energy gain of refurbished cryomodules to 75 MeV. The concept recycles the waveguide end-groups from original CEBAF cavities fabricated in the 1990s and replaces the five elliptical cells in each with a new optimized cell shape fabricated from large-grain, ingot Nb material. Eight cavities were fabricated at Research Instruments, Germany, and two cavities were built at Jefferson Lab. Each cavity was processed by electropolishing and tested at 2.07 K. The best eight cavities were assembled into ’cavity pairs’ and re-tested at 2.07 K, before assembly into the cryomodule. All but one cavity in the cryomodule were within 10% of the target accelerating gradient of 19 MV/m with a quality factor of 8·109. The performance limitations were field emission and multipacting. |
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DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-MOPCAV001 | |
About • | Received ※ 17 June 2021 — Accepted ※ 21 February 2022 — Issue date ※ 10 April 2022 | |
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MOPCAV002 | Shape Evolution of C75 Large-Grain Niobium Half-Cells During Cavity Fabrication | 255 |
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Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. The largely anisotropic deformation of large-grain Nb discs during deep drawing into half-cells poses a challenge for achieving a desired shape accuracy. Two 5-cell cavities for the C75 CEBAF cryomodule rework program have been fabricated at Jefferson Lab from large-grain Nb discs directly sliced from an ingot. The shape of the inner surface of eight half-cells has been inspected using a FARO Edge laser scanner during the fabrication process and compared to the reference shape. On average, approximately 63% of the half-cell inner surface was found to be within 0.1 mm of the reference shape and ~90% to be within 0.2 mm, after the final equator machining. Several 5-cell C75 cavities have also been fabricated at Research Instruments, Germany, and measurements of the shape accuracy using a Zeiss 3D coordinate measuring machine gave similar results. One half-cell was measured both at Research Instruments and Jefferson Lab for comparison. |
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DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-MOPCAV002 | |
About • | Received ※ 21 June 2021 — Accepted ※ 21 August 2021 — Issue date ※ 11 February 2022 | |
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TUPTEV001 | RF Experience from 6 Years of ELBE SRF-Gun II Operation | 477 |
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At the electron accelerator for beams with high brilliance and low emittance (ELBE), the second version of a superconducting radio-frequency (SRF) photoinjector was brought into operation in 2014. After a period of commissioning, a gradual transfer to routine operation took place in 2017 and 2018, so that more than 3000h of user beam have already been generated since 2019. During this time, a total of 20 cathodes (2 Cu, 12 Mg, 6 Cs2Te) were used, but no serious cavity degradation was observed. In this paper, we summarize the operational experience of the last 6 years of SRF gun operation, with special emphasis on the main RF properties of the cavity. This includes the evolution of QvsE, dark current, multipacting, but also mechanical properties such as Lorentz force detuning, helium pressure sensitivity as well as microphonics. The latter is closely connected to an active compensation by a so-called low-level RF feedback loop, which is also briefly presented. | ||
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Poster TUPTEV001 [2.148 MB] | |
DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-TUPTEV001 | |
About • | Received ※ 21 June 2021 — Revised ※ 25 December 2021 — Accepted ※ 22 February 2022 — Issue date ※ 16 April 2022 | |
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WEPFDV008 | Thermal Conductivity of Electroplated Copper Onto Bulk Niobium at Cryogenic Temperatures | 576 |
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Funding: U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177. Superconducting radio-frequency (SRF) cavities made of high-purity bulk niobium are widely used in modern particle accelerators. The development of metallic outer coatings with high thermal conductivity would have a beneficial impact in terms of improved thermal stability, reduced material cost and for the development of conduction-cooled, cryogenic-free SRF cavities. Several high-purity, fine-grain Nb samples have been coated with 2’4 mm thick copper by electroplating. Measurements of the thermal conductivity of the bimetallic Nb/Cu samples in the range 2’7 K showed values of the order of 1 kW/(m K) at 4.3 K. Very good adhesion between copper and niobium was achieved by depositing a thin Cu layer by cold spray on the niobium, prior to electroplating the bulk Cu layer. |
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DOI • | reference for this paper ※ doi:10.18429/JACoW-SRF2021-WEPFDV008 | |
About • | Received ※ 17 June 2021 — Accepted ※ 10 September 2021 — Issue date ※ 01 March 2022 | |
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WEOTEV02 |
Overview on Recent Development of Conduction Cooling Cavities | |
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Improvements in both the cooling power of 4 K crycoolers and the deposition of Nb3Sn films have spurred research and development efforts towards the operation of Nb3Sn-coated SRF cavities cooled by conduction with commercial cryocoolers. Different types of SRF cavities with frequencies between 650 MHz and 2.6 GHz and different conduction cooling schemes have been tested at different laboratories, demonstrating accelerating gradients up to ~10 MV/m. This contribution provides an overview of these and future efforts along with possible cryostat designs under evaluation for conduction-cooled SRF cavities. | ||
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