| Paper | Title | Page |
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| TUIOC06 | Study on Optimum Electron Beam Welding Condition for Superconducting Accelerating Cavities | 424 |
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| Optimizations of electron beam welding conditions might solve the quench problems and improve the accelerating field of the superconducting radio-frequency cavity. As a first step toward optimum conditions, basic properties of weld beads are studied by using niobium test pieces. Effects of a combination of a beam generator position and a welding direction on geometries of weld bead are shown. Good parameter-regions for electron beam welding, which yield full penetration welds without holes or weld spatters, are surveyed. Microscopic structures, such as pits or bumps due to poor welds, have greater influence on cavity performances, which are also our research objects. We introduce a model of the magnetic field enhancement at pits, where a formula for a magnetic field enhancement factor is given as a function of parameters that express a geometry of pit. Comparisons between calculations and vertical test results are also shown. | ||
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Slides TUIOC06 [15.958 MB] | |
| TUP007 | Vortex Penetration Field in the Multilayered Coating Model | 430 |
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A multilayered structure with a single superconductor layer and a single insulator layer deposited on a bulk superconductor is studied. General formulae for the vortex penetration-field of the superconductor layer and the magnetic field on the bulk superconductor which is shielded by the superconductor and insulator layers are derived with a rigorous calculation of the magnetic field attenuation in the multilayered structure. The formulae depend not only on the material and the thickness of the superconductor layer but also on the thickness of the insulator layer. The results can be applied to superconducting accelerating cavities with the multilayered structure. Using the formulae, a combination of the thicknesses of superconductor and insulator layers to enhance the RF breakdown field limits can be found for any given materials. (Submitted on 25 Apr 2013)
T. Kubo, Y. Iwashita and T. Saeki, arXiv:1304.6876 [physics.acc-ph](Submitted on 25 Apr 2013); arXiv:1306.4823 [physics.acc-ph](Proc. of IPAC13); arXiv:1307.0583 [physics.acc-ph](Proc. of SRF2013) |
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| TUP008 | Models of the Magnetic Field Enhancement at Pits | 433 |
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A simple model of the magnetic field enhancement at pits on the surface of superconducting accelerating cavity is proposed. The model consists of a two-dimensional pit with a slope angle, depth, width, and radius of round edge. An analytical formula that describes the magnetic field enhancement factor of the model is derived. The formula is given as a function of a slope angle and a ratio of half a width to a round-edge radius. Using the formula, the field at which vortices start to penetrate can be evaluated for a given geometry of pit.
Takayuki Kubo, arXiv:1307.5943 [physics.acc-ph](Submitted on 23 Jul 2013) |
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| TUP108 | Study on Niobium Scratch and Tantalum or Carbonaceous Contamination at Niobium Surface with Field Emission Scanner | 731 |
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| It is mandatory to investigate field emission from niobium SRF cavity surface systematically since even small field emission often limits the cavity performance terribly. The field emission strength and the number of emission sites strongly depend on niobium surface properties which are determined by its surface treatment and handling. It was found that carbonaceous contamination including carbon, oxygen, sometimes, nitrogen often segregates at CPed or EPed surface with a size of several micron to several tens of micron-meters. There is a strong doubt that this contamination causes field emission from the surface. Newly developed field emission scanner (FES) allows us to measure a distribution of the field emitting sites over a sample surface at a given field strength along with its SEM (scanning electron microscope) observation and EDX (energy dispersive x-ray) analysis. This article describes results of the FES-SEM-EDX application to carbonaceous contamination at niobium surface. | ||
| THIOA03 | Cavity Fabrication Study in CFF at KEK | 821 |
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| The construction of new facility for the fabrication of superconducting RF cavity at KEK was completed in 2011. It is equipped with the following machines; an electron-beam welding (EBW) machine, a servo press machine and a CNC vertical lathe. A chemical etching apparatus is also equipped. The study on the fabrication of 9-cell cavity for International Linear Collier (ILC) has been started from 2009 using this facility. The study is focusing on the cost reduction with keeping high performance of cavity, and the goal is the establishment of mass-production procedure for ILC. | ||
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Slides THIOA03 [7.823 MB] | |