Mechanical design aspects of the LHC beam screen

Forty-four kilometers of the LHC beam vacuum system [1,2] will be equipped with a perforated co-axial liner, the so-called beam screen. Operating between 5 K and 20 K, the beam screen reduces heat loads to the 1.9 K helium bath of the superconducting magnets and minimises dynamic vacuum effects. Constructed from low magnetic permeability stainless steel with a 50 mu m inner layer of high purity copper, the beam screen must provide a maximum aperture for the beam whilst resisting the induced forces due to eddy currents at magnet quench. The mechanical engineering challenges are numerous, and include stringent requirements on geometry, material selection, manufacturing techniques and cleanliness. The industrial fabrication of these 16 metre long UHV components is now in its prototyping phase. A description of the beam screen is given, together with details of the experimental programme aimed at validating the design choices, and results of the first industrial prototypes.