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RF Loss In and Leakage Through Thin Metal Film


Traditional RF enclosures are formed by metal bulk material, in which the field decays exponentially over a skin depth delta = Square 2/omega sigma mu sigma0. With typical bulk dimension at least one order of magnitude higher than Delta, the field outside the metal enclosure is then negligible. The surface resistance Rs presented to the RF field is 1/sigma delta. This article presents analysis of an RF shield formed by thin metal film. We find that a metal thickness Deltar of the order of skin depth, can provide an excellent RF shielding due to reflection at the interface. The surface RF loss can be reduced with proper choice of metal thickness, and heating can be reduced. The thin metal film also facilitates cooling on the back of the film via thermal conduction. For a very thin coating, the surface RF loss is inversely proportional to thickness, while inductance is proportional to thickness, and thus it is possible to customize the accelerator beam impedance through careful choice of coating thickness.

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