Design of HQ -- a High Field Large Bore Nb3Sn Quadrupole Magnet for LARP

Design of HQ – a High Field Large Bore Nb 3 Sn Quadrupole Magnet for LARP H. Felice, G. Ambrosio, M. Anerella, R. Bossert, S. Caspi, D. Cheng, D. Dietderich, P. Ferracin, A. K. Ghosh, R. Hafalia, C. R. Hannaford, V. Kashikhin, J. Schmalze, S. Prestemon, G.L. Sabbi, P.Wanderer, A.V. Zlobin Abstract— In support of the Large Hadron Collider luminosity upgrade, a large bore (120 mm) Nb 3 Sn quadrupole with 15 T peak coil field is being developed within the framework of the US LHC Accelerator Research Program (LARP). The 2-layer design with a 15 mm wide cable is aimed at pre-stress control, alignment and field quality while exploring the magnet performance limits in terms of gradient, forces and stresses. In addition, HQ will determine the magnetic, mechanical, and thermal margins of Nb 3 Sn technology with respect to the requirements of the luminosity upgrade at the LHC. Index Terms— Superconducting accelerator magnets, Nb 3 Sn, IR quadrupole, LARP IR quadrupole magnets using NbTi. This intermediate LHC upgrade and the ongoing development on HQ give a good opportunity to compare the performances of NbTi and Nb 3 Sn large aperture quads. In order to match the CERN NbTi quads aperture, the aperture of HQ will be 120 mm [7], [8]. The 2D magnetic design along with some preliminary results on the 3D magnetic design is summarized in this paper. In the last part, the mechanical structure implementing alignment features is presented. II. M AGNETIC D ESIGN A. Conductor The objectives of HQ are to reach 15 T peak field in the conductor and 200 T/m in a 120 mm aperture. A wide cable was selected to achieve this goal in a 2-layer cos2θ quadrupole and to manage the mechanical stresses in the coil. In addition, CERN plans to use the 15.1 mm wide LHC main dipole cable to fabricate the Phase 1 IR NbTi quadrupole magnets [9], [10]. In order to facilitate the comparison between NbTi and Nb 3 Sn quads, the cable width of HQ was chosen to match that of the dipole cable, 15.15 mm. The present conductor parameters are described in Table I. Due to the large size of the cable and its keystone angle, prototype cables were fabricated. The cables have been evaluated for their windability and if any strand damage occurred during cabling. TABLE I HQ D ESIGN P ARAMETERS Parameters Strand diameter Strand type Cu/non-Cu ratio Number strands Cable width (bare) Cable mid-thickness (bare) mm mm deg µm Units mm HQ design OST RRP 54/61 [11] I. INTRODUCTION the LHC baseline luminosity requires IR quadrupoles with large aperture and high gradients. The main objective of LARP is to demonstrate the feasibility of Nb 3 Sn technology for the LHC Phase 2 upgrade. Toward this goal, LARP has developed several series of Nb 3 Sn magnets: the SQ series (Subscale Quadrupole) [1], [2], the TQ series (1- meter long 90 mm aperture Technology Quadrupole) [3], [4] and the LRS series (3.6-meter Long Racetrack assembled in a common coil arrangement) [5]. The LQ series (Long Quadrupole) is under construction and is a 3.7 long version of the TQ series aiming at demonstrating the scalability of Nb 3 Sn cosine two theta quadrupole [6]. In order to meet the requirements for Phase 2 LHC upgrade, the next series of magnet will have to be designed to reach 15 T at 1.9 K in a large aperture (above 110 mm) with alignment features (to provide field quality), cooling channels and LHe containment. The objective of the LARP HQ series (1-meter long High gradient, high field Quadrupole) is to address these requirements. With the Phase 1 LHC upgrade, CERN is going to fabricate PGRADING U Manuscript received 26 August 2008. This work was supported in part 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. H.Felice, S. Caspi, D. Dietderich, D. Cheng, P. Ferracin, R. Hafalia, C.R. Hannaford, S. Prestemon and GL Sabbi are with Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA (e-mail: HFelice@lbl.gov). G. Ambrosio, R. Bossert, V. Kashiskhin and A.Zlobin are with Fermilab National Accelerator Laboratory, Batatvia, IL 60510-0500 USA. M. Anerella, A. K. Ghosh, J. Schmalze and P. Wanderer are with Brookhaven National Laboratory, NY, USA Keystone angle Insulation thickness Nb of turns IL/OL Several prototype cables have been fabricated with different thickness and keystone angles and each cable's behavior was characterized by winding tests around various pole