Results of 3-dimensional structural FE-modeling of the coil end-regions ofthe LHC main dipoles

The transition regions between the straight part and the ends of the coils of the LHC model and prototype dipole magnets are often identified as the o rigin of training quenches. In order to study how the discontinuities in th e material properties of these regions affect coil pre-stress and possibly gain more insight in the quench behavior, a program was set up at CERN to a nalyze by 3D-FEM these particular regions. The ACCEL team, who performed a similar analysis for the main quadrupoles of the Superconducting Supercolli der SSC, is entrusted with this program. In this paper we report on the res ults of 3D-modeling and analysis of the coil return end region, including t he complete cold mass, of a l-m single bore model magnet. This magnet repre sents all relevant features of the "two-in-one" LHC main dipole design conc erning the winding configuration, the collar pack, the yoke, and the outer shell representing the He-vessel. The transition region between coil ends a nd straight section is modeled by slicing the magnet down to individual col lar laminations per elementary level, The two-layer winding pack is represe nted with all individual conductor blocks, wedges, end spacers, and the int erlayer spacer. Results will be presented for load cases with pre-stress af ter assembly at room temperature, after cool-down, and under operation at m aximum current. Critical stress locations were identified in the transition into the pole free section of the magnet and in the bent part. Shimming of the coils, as well as impact from material choices and suitable alternativ es will be discussed.