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There have been several reports that photodesorption due to synchroton radiation from OFC copper chambers with machined surfaces is far lower than in stainless steel or aluminum alloy chambers. However, it is difficult to process machined surfaces for the inner surfaces of beam chambers. A surface treatment using broaching has been developed to cut the inner surface of the chamber. Tests of the photodesorption caused by synchrotron radiation in a small, broached, cylindrical cross-section chamber with a length of 30 cm have been reported. To adapt the broaching method to long chambers, prototype copper vacuum chambers with lengths of 1.8 m and 2 m have been fabricated. A chamber consists of a beam channel, a cooling channel, and a NEG pump channel. The beam channel, which has a hexagonal cross section, is broached. An ultimate pressure of 1 × 10 −8 Pa was obtained after bakeout at 200 °C for 24 h and NEG activation. |
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