Abstract
A discussion is given of the advantages of thin-walled convoluted vacuum tubes for the long arms of interferometric gravitational wave detectors currently being proposed by a number of institutions around the world. Typically the tubes will be 3 km long and 1.5 m in diameter. Pressures of ⩽ 10 −7 mbar are required for hydrogen and at least an order of magnitude lower for the sum of all the other gases. The results of tests of some of the mechanical and vacuum properties of a prototype section of convoluted tube are presented. The tube is 5 m long, 1.4 m internal diameter and is constructed from 0.91 mm thick 316L stainless steel sheet. The convolutions have a semicircular form of 20 mm radius, giving the tube a strength equivalent to a plain tube of the same diameter but 13 mm wall thickness. A specific outgassing rate of ∼3x10 −13 mbar I s −1 cm −2 is achieved by a vaccum bake at 150°C. Examination of the residual mass spectra reveals that > 99% of the gas is hydrogen.
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