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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.
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