Title: Fabrication and Test of a 3.7 m Long Support Structure for the LARP Nb3Sn Quadrupole Magnet LQS01
Abstract: Fabrication and Test of a 3.7 m Long Support Structure for the LARP Nb 3 Sn Quadrupole Magnet LQS01 P. Ferracin, G. Ambrosio, M. Anerella, B. Bingham, R. Bossert, S. Caspi, D. W. Cheng, H. Felice, A. R. Hafalia, C. R. Hannaford, F. Nobrega, S. Prestemon, G. L. Sabbi, J. Schmalzle, F. Trillaud, P. Wanderer, A.V. Zlobin Abstract—The 3.7 m long quadrupole magnet LQS01 represents a major step of the US LHC Accelerator Research Program (LARP) towards the development of long Nb 3 Sn accelerator quadrupole magnets for a LHC Luminosity upgrade. The magnet support structure is a scale up of the 1 m long Technology Quadrupole TQS design with some modifications suggested by TQS model test results. It includes an aluminum shell pre-tensioned over iron yokes using pressurized bladders and locking keys (bladder and key technology). The axial support is provided by two stainless steel end plates compressed against the coil ends by four stainless steel rods. The structure, instrumented with strain gauges, has been fabricated and assembled around four aluminum “dummy coils” to determine pre-load homogeneity and mechanical characteristics during cool-down. After presenting the main magnetic and mechanical parameters of LQS01, we report in this paper on the design, assembly, and test of the support structure, with a comparison between strain gauges data and 3D finite element model results. Index Terms— LARP, Nb 3 Sn, Quadrupole magnet Fig. 1. LARP shell-based (S) magnets (from left to right in chronological order and in scale): Subscale Quadrupole SQ (2004), Technology Quadrupole TQS (2005), Long Racetrack LRS (2006), and Long Quadrupole LQS (under development). I. INTRODUCTION A S part of the LHC Accelerator Research Program (LARP [1], [2]), three US national laboratories (BNL, FNAL, and LBNL) are developing the 3.7 m Long Quadrupole magnet LQS01, which represents a fundamental step toward the development of Nb 3 Sn magnets for a future LHC IR upgrade. LQS will incorporate four cosϑ-type coils fabricated at BNL and FNAL [3]-[5], and it will be tested in a shell- based support structure designed, fabricated, and assembled at LBNL. Shell-based support structures have been originally developed by the LBNL Superconducting Magnet Program to cope with the needs of high field Nb 3 Sn magnets [6]-[8]. Manuscript received 19 August 2008. This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, High Energy Physics Division, U. S. Department of Energy, under Contract No. DE-AC02-05CH11231. P. Ferracin, B. Bingham, S. Caspi, D. W. Cheng, H. Felice, A. R. Hafalia, C. R. Hannaford, S. Prestemon, G. L. Sabbi, and F. Trillaud are with Lawrence Berkeley National Lab, Berkeley, CA 94720, USA (phone: 510- 486-4630; fax: 510-486-5310; e-mail: [email protected]). G. Ambrosio, R. Bossert, F. Nobrega, and A.V. Zlobin are with Fermilab National Accelerator Laboratory, Batavia, IL 60510, USA. M. Anerella, J. Schmalzle, and P. Wanderer are with Brookhaven National Laboratory, Upton, NY 11973-5000, USA. Because of large electro-magnetic forces acting on a brittle superconducting material, these magnets require precise control of the coil pre-load. The main features of shell-based structures are the following: 1) external segmented aluminum shell; 2) iron yoke quadrants separated by open gaps during all magnet operations; 3) assembly attained by joining two sub- assemblies; 4) pre-loading applied with water pressurized bladders; 5) maximum coil stress reached after cool-down; 6) coil ends supported by end-plates and axial rods. The LQS support structure design relies on the experience gained during the development of several LARP magnets (see Fig. 1). The Sub-scale Quadrupole magnet SQ [9]-[12], tested in 2004, was the first magnet where the shell-based structure was applied to a quadrupole configuration. It used 300 mm long racetrack coils, and included alignment features among all the components. The Technology Quadrupole Shell-based magnet TQS [13]-[19], tested in 2005, applied the concept to 1 m long cosϑ-type coils. Alignment features were not included in the design. In 2006 the Long Racetrack Shell-type magnet LRS [20]-[24] was fabricated and tested: it was the first magnet adopting shell-based structure for long coils, and it implemented two 3.6 m long racetrack coils assembled in a common-coil configuration. The LQS structure is basically an extension of the TQS structure, with some additional features to facilitate assembly and provide alignment of the structural components. The coil-structure alignment, excluded in the LQ magnet design, will be implemented in the High-field Quadrupole magnet HQ [25], [26]. In this paper, we provide a detailed description of LQS01 cable and magnet design in Sec. II. The results of magnetic and mechanical analyses are presented in Sec. III and Sec. IV, while the assembly procedure is discussed in Section V. Finally, Sec. VI describes the cool-down test of a 0.85 m long version of the structure assembled with Al dummy coils.