Measurement and analysis of axial end forces in a full-length prototype ofLHC main dipole magnets

A full-length, twin aperture prototype (MBP2N1) dipole magnet for the LHC p roject was assembled at CERN with collared coils delivered by industry. The design of this prototype is close to that foreseen for the dipole series m anufacture as far the coil geometry and that of the yoke components are con cerned. The. bolts that transfer the axial magnetic forces from the coil en ds to the cold mass end plates were instrumented to verify the axial coil s upport, These axial forces were initially measured after partial assembly, during a standard and an accelerated cool down Introduction to 1.9 K, and d uring magnet excitation up to 9.2 T, High force levels were observed, trigg ering a comparison with analytical models and measurements routinely made o n l-m single aperture dipole models. The prototype magnet was re-assembled with lower initial axial force settings and with additional instrumentation , to monitor these forces during the entire assembly process, and re-tested , to possibly correlate axial forces with training behaviour. This paper re ports about the; experimental observations and provides models towards thei r understanding.