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| TUP028 | Investigation of Spatial Variation of the Surface Resistance of a Superconducting RF Cavity | cavity, superconducting-RF, SRF, superconductivity | 483 |
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Funding: NSF Cornell has recently completed a single cell temperature mapping system with a resolution of a few tenths of a millikelvin, corresponding to a surface resistance resolution of 1 nOhm. A superconducting RF cavity was tested using temperature mapping and the surface resistance was extracted from the temperature mapping data as function of position on the cavity surface. The surface resistance was profiled across the surface of the cavity between 5 and 35 MV/m and at different temperatures between 1.6 and 2.1 K. From BCS fitting of the local surface resistance, the spatial variation and the field dependence of the mean free path, energy gap, and residual resistance was found. These studies give interesting new insight into the degree of variation of the properties of the superconductor over the surface of the cavity. |
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| TUP029 | Heat Treatment of SRF Cavities in a Low-Pressure Atmosphere | cavity, vacuum, SRF, niobium | 487 |
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Funding: NSF Recent results from FNAL on baking superconducting RF cavities at high temperatures in a low-pressure atmosphere of a few mTorr indicate that such treatments can increase the medium field quality factor. In this paper we report on studies from Cornell, giving new insight into the mechanism behind this effect. |
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| TUP074 | Development of an Optimized Quadrupole Resonator at HZB | quadrupole, cavity, niobium, focusing | 614 |
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Funding: EuCARD II Current superconducting cavities are generally made of solid niobium. A possibility to reduce cost as well as increase accelerating fields and, essential for CW applications, the quality factor is to use thin-film coated cavities. Measuring and understanding the RF-properties of superconducting thin films, specifically the surface resistance at the operating field and frequency, is needed to drive forward this development. Presently, only few facilities exist capable of measuring the surface resistance of thin films samples with a resolution in the nano-ohm range at L-Band. We describe here a dedicated test stand consisting of a quadrupole resonator that was constructed at the Helmholtz Zentrum Berlin. Starting with 400-MHz quadrupole resonator developed at CERN, the design was adapted and optimized for resolution and reduced peak electric field to 433 MHz (making available the higher harmonic mode at 1,3GHz) using simulation data obtained with CST Microwave Studio as well as ANSYS. The relevant figures of merit have been improved, giving the possibility to perform measurements with high resolution at high field levels. |
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| THP027 | Multipactor Analysis of the HWR at RISP | cavity, electron, simulation, coupling | 955 |
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| We report on the progress of the HWR development at RISP. The multipaction of the HWR was studied using CST-PS (PIC) solver and multipacting band is predicted. Additional considerations were given to see the effects of the coupling ports and the coupler on the multipaction. We present the modified cavity design without multipaction at our operation accelerating voltage~1.2MV. | |||
| THP029 | Simulation of Mechanical Resonances of SRF Cavities in Low Beam Current CW Operation | cavity, operation, simulation, cryomodule | 962 |
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| The low beam current for CW operation of the Project X requires cavities to be mechanically optimized to operate at a high loaded Q and thus, low bandwidth with higher sensitivity to microphonics. The essential source of microphonics detuning is fluctuations in the helium pressure df/dp. Last year’s several methods for reducing df/dp has been proposed. One of the other possible sources of RF frequency instability is mechanical resonances. The cavity could be driven out of operating frequency by the mechanical deformations due to vibrations caused by external factors. In this paper we present the COMSOL multiphysics algorithm developed for evaluation of operating frequency shift due to mechanical resonances in SC cavities. We discuss the results of simulations for 5-cell elliptical 650 MHz β=0.9 cavities. The comparison of COMSOL simulations and measurements of ILC type cavities in Horizontal Test Stand at Fermilab is presented. | |||
| THP031 | Superconducting Test of the 56 MHz SRF Quarter Wave Resonator for RHIC | cavity, SRF, electron, simulation | 969 |
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Funding: This work was supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. DOE. A 56 MHz superconducting RF cavity will be the first quarter wave resonator (QWR) installed in a high energy storage ring. It is expected to boost the luminosity of the Relativistic Heavy Ion Collider by more than 60% after installation. In this paper, we discuss the cavity parameters and design features. We report the results from the first vertical test of this cavity at 4 K. |
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| THP034 | Multipacting Suppression in a Single Spoke Cavity | cavity, electron, simulation, operation | 975 |
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| Spoke cavities are good candidates for the low and medium β section of a high intensity proton or ion accelerator. For many high intensity accelerators, stability and reliability are the most important properties. Currently, one of the key issues of spoke cavity performance is multipacting, which may cause instability during operation. Multipacting in a spoke cavity has a troublesome characteristic as it presents a continual barrier over a wide gradient range, usually in the range of operation from 3MV/m to 15MV/m. A good surface processing can improve the secondary electron emission yield. However, the complex 3D structure makes it not easily achievable as with the elliptical cavity variants. Suppressing multipacting in the design stage is clearly advantageous. This paper will present a multipacting study based on the PKU-I spoke cavity. A systematic correlation between geometric parameters and multipacting behaviors is obtained. Based on this study a new geometry of single spoke cavity called the ‘balloon’ variant is proposed. | |||
| THP038 | Development and Performance of a High Field TE-Mode Sample Host Cavity | cavity, niobium, simulation, SRF | 985 |
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Funding: US National Science Foundation Career award PHY-0841213 A TE-mode 4 GHz sample host cavity has been designed and constructed at Cornell for the purpose of testing wafers of niobium and other candidates for the construction of SRF cavities. Simulations made using CLANS and ACE3P indicate that the peak magnetic field on the sample plate will reach approximately 120 mT before a quench occurs on the surface of the cavity due to thermal runaway. This quench field can be further increased using a 1400 C treatment to improve the thermal conductivity of the niobium bulk and a 120 C treatment to minimise the BCS surface resistance of the cavity walls. Such an improvement would put peak fields of 170 mT within reach of this cavity. Results of the cavity design, fabrication and first vertical test are presented and discussed. *Development of Superconducting RF Sample Host Cavities and study of Pit-Induced Cavity Quench, Yie Xie, PhD Thesis, Cornell University, Jan 2013 |
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| THP080 | SRF Cavity Tuning for Low Beam Loading | cavity, operation, cryomodule, vacuum | 1110 |
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| The design of 5-cell elliptical 650 MHz β=0.9 cavities to accelerate H− beam of 1 mA average current in the range 467-3000 MeV for the Project X Linac is currently under development at Fermilab. The low beam current enables cavities to operate with high loaded Q’s and low bandwidth, making them very sensitive to microphonics. Mechanical vibrations and the Lorentz force can drive cavities off resonance during operation; therefore the proper design of the tuning system is very important part of cavity mechanical design. In this paper we review the design, performance, operation, reliability and cost of fast and slow tuners for 1.3 GHz elliptical cavities. We also present a design of the slow and fast tuners for 650 MHz β=0.9 cavities based on this experience. The HV in the new design is equipped with the tuners located at the end of the cavity instead of the initially proposed blade tuner located in the middle. We will present the results of ANSYS analyses of mechanical properties of tuners. | |||
| THP082 | Fast Detuning Experiment on an SRF Cavity | cavity, cryomodule, experiment, storage-ring | 1118 |
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Funding: Work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357. Short Pulse X-ray beamlines occupy a limited number of sectors after the APS Upgrade. The majority of APS users will not participate in the SPX experiment. As user operation requires the best beam availability, it is important that any SPX-related circuit trip that requires the extinguishment of rf power should not affect overall beam availability. As such, it is necessary to de-couple the SRF cavities from beam when such an rf trip happens. An example of such trip is that the rf window arcing has to be stopped within 1 ms, before serious damage occurs to the ceramic. As the rf amplifier shuts down the rf output, beam-driven cavity power has to be reduced, too. If cavity can be detuned fast enough and far enough away from its resonance, the beam does not have to be aborted. The SPX0 tuner is equipped with a fast response Piezo actuator in the cavity tuner stack. Such a Piezo may be able to provide a quick jolt of the cavity to provide detuning capability for the purpose of maintaining the beam in the event of an rf trip. In this paper, we describe the experimental setup and results obtained, and discuss its effectiveness for beam operation. |
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| THP087 | LLRF Tests of XFEL Cryomodules at AMTF: First Experimental Results | cavity, cryomodule, LLRF, operation | 1132 |
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| In preparation for the series production of cryomodules for the European X-ray Free Electron Laser (XFEL), three pre-series cryomodules and several prototypes have been produced and tested at the Cryomodule Test Bench (CMTB) and at the Accelerating Module Test Facility (AMTF) in DESY. Among the numerous tests performed on the modules, the low-level radio frequency (LLRF) tests aim at characterizing the performance of the modules from an RF controls perspective. These integration tests must take into account cavity tuners, cavity motorized couplers, quench gradients, microphonics, piezo control and the overall gradient performance of the cryomodule under test. In this paper, the LLRF-specific tests are summarized and the first experimental results obtained at CMTB and AMTF are presented. | |||
| THP095 | Error Analysis for Vertical Test Stand Cavity Measurements at Fermilab | cavity, detector, simulation, SRF | 1148 |
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| Overview of Vertical Test Stand (VTS) facility at Fermilab is presented. Uncertainty calculations for the measurements of quality factor and accelerating field are described Sources of uncertainties and assumptions on their correlations are reviewed. VTS hardware components with non-negligible instrumental errors are discussed. Relative contributions of individual sources to the total uncertainties are assessed. Stability of VTS test results with respect to potential mismeasurements of calibration coefficients and decay constant are studied. | |||