| Paper | Title | Page |
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| TUPD038 | Beam Test of a Movable Collimator (Mask) with Low Beam Impedance | 1511 |
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A movable collimator with low beam impedance for future high-intensity machines has been investigated in KEK*. The metal head of the collimator is supported by a dielectric material in order to reduce the interference with beams. The first test model was installed into the KEK B-factory (KEKB) positron ring last year. The head and the support was alumina ceramic, but only the head was coated by copper to realize a conductive layer. The support, however, was finally melted during the beam operation due to the overheating by intense electromagnetic fields induced by bunches. Based on the experience, the design was revised and the second test model was manufactured, where the head and the support were made of graphite and artificial diamond, respectively. Graphite is a conductive material with high thermal strength, and diamond, on the other hand, is a dielectric material with high thermal conductivity as well as the strength. The second test model is installed in the spring of this year, and tested again with beams during the beam operation to prove the principle. The results of the beam tests will be presented here.
* Y. Suetsugu, K. Shibata, A. Morishige, Y. Suzuki, M. Tsuchiya, “Design Study of a Movable Mask with Low Bema Impedance”, PRST-AB, 9, 2006, 103501. |
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| TUPP071 | Development of TiN Coating System for Beam Ducts of KEK B-factory | 1700 |
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| A titanium nitride (TiN) coating system for the copper beam ducts of KEK B-factory (KEKB) was developed to reduce the secondary electron yield (SEY) from the inner surface, which would mitigate the electron cloud instability. The coating was done by DC magnetron sputtering of titanium in argon and nitrogen atmospheres. The duct was set vertically, and a titanium cathode rod was hung from the top on the center axis of the duct. A magnetic field was supplied by a movable solenoid coil placed outside of the duct. Preliminary experiments using small copper samples showed that a 200-nanometer-thick TiN film coated at 150 degree is the best from the viewpoints of SEY and adhesion strength. The SEY of the coated sample decreased to 60% of that of non-coated copper after an electron dose of 0.01 C/mm2, and the maximum SEY was 0.84. Using this system, five ducts with a length of up to 3.6 m were successfully coated. Some of them were installed into the KEKB positron ring last summer, and no problem was found in the following beam operation with a beam current of up to 1.6 A. One coated duct with an electron monitor was installed this winter, and the effect of the coating will be checked. |