Hybrid Cu-Al beam pipe for KEK B factory

Hybrid Cu-Al beam pipe is proposed for KEK B factory. The pipe is based on the idea that better characteristics of each material are utilized to obtain lower cost and photodesorption yield comparable to that of all copper vacuum beam pipe. Copper is set to the part irradiated directly with photons of synchrotron radiation and aluminum alloy is set to the part irradiated with reflected photons of synchrotron radiation. A fabricated model of the hybrid Cu-Al beam pipe is shown and can be realized using trivial technique. For the present, measured desorption yield of aluminum alloy is evaluated about 5 times higher than that of copper. Using the value, estimated photodesorption yield is about 3 times higher than that of all copper beam pipe at the photon dose larger than 1021 photons/m. The photodesorption yield of the aluminum alloy must be reduced and the several methods are suggested to obtain a comparable yield with copper. The estimated radiation outside of the hybrid beam pipe in the normal bending section for high energy ring and low energy ring for KEK B factory is comparable and wiggler section needs one order of magnitude dense shield compared with that of TRISTAN accumulation ring. Estimated cost of the hybrid beam pipe is one third of all copper beam pipe and is 0.6 million yen per meter. (author)