Design and Fabrication of a Supporting Structure for 3.6 m Long Nb$_{3}$Sn Racetrack Coils

As part of the LHC accelerator research program (LARP), three US national laboratories (BNL, FNAL, and LBNL) are currently engaged in the development of superconducting magnets for the LHC interaction regions (IR) beyond the current design. As a first step towards the development of long Nb3Sn quadrupole magnets, a 3.6 m long structure, based on the LBNL subscale common-coil magnet design, will be fabricated, assembled, and tested with aluminum-plate "dummy coils". The structure features an aluminum shell pre-tensioned over iron yokes using pressurized bladders and locking keys (bladder and key technology). Pre-load homogeneity and mechanical responses are monitored with pressure sensitive films and strain gauges mounted on the aluminum shell and the dummy coils. The details of the design and fabrication are presented and discussed, and the expected mechanical behavior is analysed with finite element models.