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| TUPEA077 | Low-Secondary Electron Yield of Ferrromagnetic Materials and Magnetized Surfaces | electron, vacuum, cavity, superconducting-cavity | 1500 |
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We are presenting first results of direct measurements of the secondary electron emission yield (SEY) for several magnetic materials like ferrites at energies of primary electrons from 5 to 1000 eV. In order to minimize the impact of surface charging, the primary electron beam had a short pulse modulation of 400ns with a very low repetition rate. This paper discusses a method of developing a secondary-electron-suppressing highly textured ferrite surface with low SEY by depositing a layer of very fine ferrite particles onto a substrate. The experimental results indicate that the SEY of the particulate ferrite surfaces is much lower than that of flat ferrites. In comparison we have confirmed that ordinary carbon coating with rather large grain size returns SEY value close to unity. However, a surface with very finely powdered carbon has a much smaller secondary emission yield of about 0.5, but the adhesion of these carbon powders to the surface is often not reliable enough for many applications. As a remarkable fact it has been found that gold- and also carbon-coated ferrites have SEY peak values lower than unity up to 1000eV. |
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| WEPEA026 | On Multipacting-free Waveguide for High Current Light Source | electron, simulation, vacuum, positron | 2541 |
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The effect of surface roughness on the secondary electron emission from a sandblasted surface is investigated using a Monte-Carlo method. Sandblasted surfaces can significantly reduce the secondary emission yield and have a large sensitivity to the percentage of surface roughness. |
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| WEPEC002 | Titanium Nitride Coating as a Multipactor Suppressor | vacuum, electron, target, lattice | 2887 |
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LAL-Orsay is developing an important effort on R&D and technology studies on RF power couplers for superconductive cavities. One of the most critical components of those devices is the ceramic RF window that allows the power flux to be injected in the coaxial line. The presence of a dielectric window on a high power RF line has a strong influence on the multipactor phenomena. The most important method to reduce the multipactor is to decrease the secondary emission yield of the ceramic window. Due to its low Secondary electron Emission Yield (SEY), TiN thin film is used as a multipactor suppressor coating on RF ceramic coupler windows. In this frame work, TiN deposition was made by magnetron reactive sputtering. XPS and XRD analysis were performed to control the film composition and stoechiometry. Coating thickness was optimized so that the TiN coating effectively reduces the SEY but does not cause excessive heating, due to ohmic loss. For this purpose, SEY measurements on covered and uncovered TiN Alumina substrates, multipactor level breakdown on TiN coated Cupper substrates and RRR measurements were performed for different deposit thicknesses. |
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| WEPEC062 | High Power Coax Window | SRF, cryogenics, linac, vacuum | 3034 |
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A superconducting RF (SRF) power coupler capable of handling 500 kW CW RF power is required for present and future storage rings and linacs. There are over 35 coupler designs for SRF cavities ranging in frequency from 325 to 1500 MHz. Coupler windows vary from cylinders to cones to disks, and RF power couplers are limited by the ability of ceramic windows to withstand the stresses due to heating and mechanical flexure. We propose a novel robust co-axial SRF coupler design which uses compressed window technology. This technology will allow the use of highly thermally conductive materials for cryogenic windows. Using compressed window techniques on disk co-axial windows will make significant improvements in the power handling of SRF couplers. We present the bench test results of two window assemblies back to back, as well as individual window VSWR in EIA3.125 coax. A vacuum test assembly was made and the windows baked out at 155C. The processes used to build windows is scalable to larger diameter coax and to higher power levels. |
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| WEPEC079 | Design and Prototype Progress toward a Superconducting Crab Cavity Cryomodule for the APS | cavity, HOM, damping, niobium | 3061 |
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A squashed, elliptical supercondconducting (SC) cavity with waveguide dampers on the beam pipes has currently been chosen as the baseline design [1] for the Short Pulse X-ray (SPX) project at the Advanced Photon Source (APS). An alternate cavity design, with a waveguide damper located directly on the cavity cell for improved damping characteristics, has also been designed and cold-tested with promising results. In either case, eight cavities would be operated CW in a single cryomodule at 2K to produce an electron bunch chirp of 4MV at a frequency of 2.815 GHz. Detailed analysis of multipactoring (MP), lorentz force detuning (LFD), and the thermal properties of the baseline design has led to an engineering specification of the basic parameters of the cryomodule. |