Hybrid Cu–Al beam pipe for KEK B factory

Abstract

A hybrid Cu–Al beam pipe is proposed for the KEK B factory. The pipe design is based on the idea that the best characteristics of each material should be utilized to obtain lower cost and a photodesorption yield comparable to that of an all-copper vacuum beam pipe. Copper is used in the part directly irradiated by synchrotron radiation photons while aluminum alloy is used in the parts irradiated only by reflected photons. A fabricated model of the hybrid Cu–Al beam pipe is presented, and can be realized using standard manufacturing techniques. For the present, the desorption yield of aluminum alloy is estimated as about five times higher than that of copper. Using this value, the estimated photodesorption yield is about three times higher than that of an all-copper beam pipe, at a photon dose greater than 1021 photons/m. The photodesorption yield of the aluminum alloy must be reduced, and several methods are suggested to obtain a yield comparable to copper. Using EGS4, the estimated radiation levels outside of the hybrid beam pipe in the normal bending sections of both the high energy ring and the low energy ring for the KEK B factory are comparable with those in the existing TRISTAN accumulation ring. In the wiggler sections, however, an additional order of magnitude in shielding is required to reach the same levels. The present estimated cost of the hybrid beam pipe is one third that of an all-copper beam pipe and is 0.6 million yen per meter.