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| WEPAF080 | Beam Size Measurements Based on Movable Quadrupolar Pick-ups | pick-up, emittance, alignment, quadrupole | 2028 |
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| Measurements with quadrupolar pick-ups (PU) have attracted particular interest as non-intercepting diagnostics for determining the transverse beam size. They are based on processing the signals of an electromagnetic PU for the extraction of the second-order moment, which contains information about the beam size. Despite the simplicity of the concept, quadrupololar measurements have always been highly challenging in reality. This comes from the fact that the quadrupolar moment constitutes only a very small part of the total PU signal dominated by the intensity and the position signals. Therefore, the beam size information can easily be lost due to small imperfections in the signal processing chain, such as asymmetries in the electronics and cables. In this paper, we present a new method for quadrupolar measurements using movable PUs. Through position and aperture scans, our technique minimizes the parasitic beam position signal and takes into account imperfections of the PU, cables and electronics, thus enabling an efficient auto-calibration of the measurement system. Preliminary studies, using collimators with embedded electrostatic PUs in the LHC at CERN, have shown very promising results. | |||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAF080 | ||
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| THPAL015 | Evaluation of superconducting characteristics on the thin-film structure by NbN and Insulator coatings on pure Nb substrate | cavity, SRF, radio-frequency, electromagnetic-fields | 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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| THPAL105 | Lower Critical Field Measurement System of Thin Film Superconductor | controls, experiment, simulation, SRF | 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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| THPAL140 | Rework Recipe Development, Analysis and Results of Select 9-Cell Cavities for LCLS-II | cavity, niobium, site, linac | 3968 |
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Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The SLAC National Accelerator Laboratory is currently constructing a major upgrade to its accelerator, the Linac Coherent Light Source II (LCLS-II). Several Department of Energy laboratories, including the Thomas Jefferson National Accelerator Facility (JLab) and Fermi National Accelerator Laboratory (FNAL), are collaborating in this project. The cryomodules for this project each consist of eight 1.3-GHz cavities produced by two vendors, Research Instruments GmbH in Germany (RI*) and Ettore Zanon S.p.a. in Italy (EZ*), using niobium cell material from Tokyo Denkai Co., Ltd. (TD) and Ningxia Orient Tantalum Industry Co., Ltd. (OTIC/NX)). During the initial production run, cavity performance from one of the vendors (Vendor A) was far below expectation. All the cavities had low Q0, later attributed to minimal EP as well as high-flux-trapping NX material, early quench behaviour below 18 MV/m, with many having Q0 roll-off at 12-16 MV/m. Production was stopped multiple times over the following 6 months, with test batches of cavities being made to ascertain the root cause of the problem. The final root cause of the problem was found to be inappropriate grinding of the RF surface prior to welding which left normal conducting inclusions in the surface. In addition, most cavities showed internal and external weld spatter which required post weld grinding and a very rough surface from operating the electropolishing machine in an etching rather than polishing regime. All issues have been corrected on new cavities and rework is underway on the originally effected cavities. |
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| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL140 | ||
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