Design Studies of Nb3Sn High-Gradient Quadrupole Models for LARP

1LL05 Design Studies of Nb 3 Sn High-Gradient Quadrupole Models for LARP GianLuca Sabbi, Nikolai Andreev, Shlomo Caspi, Daniel Dietderich, Paolo Ferracin, Arup Ghosh, Vadim Kashikhin, Al Lietzke, Alfred McInturff, Igor Novitski, Alexander Zlobin Abstract—Insertion quadrupoles with large aperture and high gradient are required to achieve the luminosity upgrade goal of 10 35 cm -2 s -1 at the Large Hadron Collider (LHC). In 2004, the US Department of Energy established the LHC Accelerator Research Program (LARP) to develop a technology base for the upgrade. Nb 3 Sn conductor is required in order to operate at high field and with sufficient temperature margin. We report here on the conceptual design studies of a series of 1 m long “High- gradient Quadrupoles” (HQ) that will explore the magnet performance limits in terms of peak fields, forces and stresses. The HQ design is expected to provide coil peak fields of more than 15 T, corresponding to gradients above 300 T/m in a 90 mm bore. Conductor requirements, magnetic, mechanical and quench protection issues for candidate HQ designs will be presented and discussed. Index Terms—Superconducting accelerator magnets, Nb 3 Sn, final focus quadrupoles. I. Short Sample Gradient [ T/m ] NbTi Upgrade CERN-HHH [2] LBNL & INFN [3] FNAL [4] KEK & FNAL NbTi LHC IR HQ LBNL [6] FNAL [4]-[5] TQ [8]-[9] & LQ [10] HQ-130 Higher Performance Coil Aperture [ mm ] Fig. 1. Parameters of NbTi and Nb 3 Sn quadrupole designs for the LHC IR. I NTRODUCTION staged upgrade of the LHC and its injectors is under study to achieve a luminosity of 10 35 cm -2 s -1 , a 10-fold increase with respect to the baseline design [1]. Replacing the first-generation NbTi IR quadrupoles with higher performance magnets is one of the required steps in this direction. Although improved designs based on NbTi are being considered as an intermediate solution [2], Nb 3 Sn conductor is required to meet the ultimate performance goals for both operating field and temperature margin. Several design studies of Nb 3 Sn IR quadrupoles for this application have been performed in the past several years [3-6]. Under typical upgrade scenarios, the new magnets will provide increased focusing power to double or triple the luminosity, and at the same time will be able to operate under radiation loads corresponding to the 10 35 cm -2 s -1 luminosity target. Starting in 2004, the LHC Accelerator Research Program (LARP) has been coordinating the US effort to develop prototype magnets for the luminosity upgrade [7]. At present, a series of 1-meter long “Technology Quadrupoles” (TQ) with 90 mm aperture and 220-250 T/m gradient are being fabricated and tested [8-9]. The TQ models are intended to Manuscript received August 30, 2006. This work was supported by the Director, Office of Science, U.S. Department of Energy under Contract DE- AC02-05CH11231. G. Sabbi, S. Caspi, D. Dietderich, P. Ferracin, A. Lietzke, A. McInturff are with Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (phone: 001 510 495 2250; fax: 001 510 486 5310; e-mail: glsabbi@lbl.gov). N. Andreev, V. Kashikhin, I. Novitski, A. Zlobin are with Fermi National Accelerator Laboratory, Batavia, IL 60510. A. Ghosh is with Brookhaven National Laboratory, Uptown, NY 11973. A serve as basis for a series of 4-meter long quadrupoles (LQ) with same aperture and gradient [10], and for a series of 1 m long “High-gradient Quadrupoles” (HQ) which are the focus of the present paper. A plot of the (aperture, gradient) parameter space comparing the HQ to other quadrupole designs for the LHC IR is shown in Fig. 1. II. D ESIGN O BJECTIVES The main goal of the HQ design study is providing a basis for the development of a series of model quadrupoles exploring the performance limits in terms of peak fields, forces and stresses. In addition, the results will benefit follow- up studies (beam optics, radiation deposition, cryogenics) directed towards a self consistent IR design for the LHC luminosity upgrade. The HQ models are expected to demonstrate peak fields in the coils of 15 T or higher. A coil aperture of 90 mm, corresponding to gradients above 300 T/m, was chosen as the baseline. This aperture choice has practical advantages in the context of the LARP program, due to the possibility of sharing tooling and parts with the TQ series, decreasing the development time and cost. However, a 90 mm aperture is at the lower boundary of the range being considered for the LHC luminosity upgrade [11]. At present, the 90 mm case is used as a reference for comparing different design approaches. In parallel, a detailed analysis of the benefits and costs of moving to larger apertures is underway. We expect that the results of the conceptual design analysis and optimization will still be applicable to model magnets with apertures in the range being considered.