Prototype development of a warm bore insert for the LHC magnet measurements

To allow the measurements of the superconducting LHC magnets up to their nominal field with well-proven, standard techniques, easy access into the apertures is required at ambient temperature and atmospheric pressure. A warm bore anti-cryostat is inserted into the cold bore vacuum pipe of the magnet, where the evacuated radial gap between these two parts serves as thermal insulation. To allow for maximum accessible cross-section during the measurements, the small radial gap of 3.5 mm has to accommodate superinsulation, support spacers and electrical heaters for the thermalization. Design aspects, related to the high magnetic fields, quenches, mechanical loads, vacuum, reliability and ease of handling have to be addressed. The design of the anti-cryostat and the cryogenic test of a prototype model are described. The heat load on the cold mass of the magnet by this prototype was below one watt per meter