Development and Test of TQC models, LARP Technological Quadrupole Magnets

Development and Test of TQC models, LARP Technological Quadrupole Magnets R.C. Bossert, G. Ambrosio, N. Andreev, E. Barzi, R. Carcagno, S. Feher, V.S. Kashikhin, V.V. Kashikhin, F. Nobrega, I. Novitski, D. Orris, M. Tartaglia, A.V. Zlobin, Fermilab, S. Caspi, D. Dietderich, P. Ferracin, A.R. Hafalia, G. Sabbi, LBNL Abstract—In support of the development of a large-aperture Nb3Sn superconducting quadrupole for the Large Hadron Collider (LHC) luminosity upgrade, two-layer quadrupole models (TQC and TQS) with 90mm aperture are being constructed at Fermilab and LBNL within the framework of the US LHC Accelerator Research Program (LARP). This paper describes the development and test of TQC01b, the second TQC model, and the experience during construction of TQE02 and TQC02, subsequent models in the series. ANSYS analysis of the mechanical structure, its underlying assumptions, and changes based on experience with TQC01 are presented and discussed. Construction experience, in-process measurements, and modifications to the assembly since TQC01 are described. The test results presented here include magnet strain and quench performance during training of TQC01b, as well as quench studies of current ramp rate dependence. Index Terms— LARP, LHC IR, Nb 3 Sn, quadrupole magnet, collars, yoke, skin. the critical current limit, quenches appeared at the outer coil mid-plane in two coils, resulting from cable degradation at those positions. Low preload in the magnet body, coupled with higher preload at the ends, allowed longitudinal movement of the coils at the mid-planes, resulting in degradation and limiting the current level. Skin Stress Relief Slot in inner pole Collar/Yoke Radial Shim Collaring Key Yoke Control Spacer Collar Azimuthal Coil Midplane Shim I. INTRODUCTION TQC style models have been built for LARP [1] since the initial testing of TQC01 [2]. TQC01b, made from coils previously used in TQC01 and TQS01 [3], has been built and tested. TQE02 (E stands for “coil exchange”), made from coils previously used in TQS02 [4], and TQC02, made of four new coils, are both currently under construction, scheduled to be tested early in FY08. Construction methods have been refined, instrumentation improved and new in- process measurements have been developed since the fabrication of TQC01. EVERAL Fig. 1. TQC structure and shim system. S III. C ONSTRUCTION I MPROVEMENTS A. Refinement of Assumptions about Coil Properties. To achieve the proper preload when using the TQC structure, the coils must be shimmed azimuthally at the midplanes and radially between the collars and yoke, at the positions shown in Fig. 1. To establish the shims needed, it is important to know the Modulus of Elasticity and azimuthal size of the individual coils. An elastic MOE of 40 GPa was assumed for both the analysis and readout of instrumentation in TQC01. Preload was inferred during construction from strain gauges mounted to the interior surface of the coils. Use of a high coil MOE resulted in an underestimation of the shim size needed as well as a misinterpretation of the preload level during construction. Beginning with TQC01b, analysis is based on plastic behavior of coils derived from previous measurements taken at FNAL [6], with an MOE of 20 GPa on the first application of pressure, followed by a permanent change in size and an approximately 40 GPa MOE on subsequent pressings, as shown in Fig. 2. Preload is inferred by strain gauges mounted to the inside surface of the inner poles, which may be made of either bronze or titanium. II. TQC01 E XPERIENCE TQC01, the first model completed with the TQC style structure (shown in Fig. 1), was tested in FY06 [5]. Quench current plateau at 4.5K was limited to 70% of the critical current limit of the conductor by insufficient preload within the magnet straight section. At 1.9K, after reaching 85% of Manuscript received August 27, 2007. This work was supported by the U.S. Department of Energy. R.C. Bossert, G. Ambrosio, N. Andreev, E. Barzi, R. Carcagno, S. Feher, V.S. Kashikhin, V.V. Kashikhin, M.J. Lamm, F. Nobrega, I. Novitski, D. Orris, M. Tartaglia, and A. Zlobin are with Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, Il. USA Phone: 630-840-2867, fax: 630- 840-8079, e-mail: bossert@ fnal.gov). S. Caspi, D.T. Dietderich, P Ferracin, R. Hafalia and G.L. Sabbi are with Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA.