Test Results of HD2, A High Field Nb3Sn Dipole with A 36 MM Bore

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TEST RESULTS OF HD2, A HIGH FIELD NB 3 SN DIPOLE WITH A 36 MM BORE * P. Ferracin # , LBNL, Berkeley, CA 94720, U.S.A. Abstract The Superconducting Magnet Program at Lawrence Berkeley National Laboratory (LBNL) has developed the 1 m long Nb 3 Sn dipole magnet HD2. With tilted (flared) ends to avoid obstructing a 36 mm clear bore, HD2 represents a step towards the use of block-type coils in high-field accelerator magnets. The coil design has been optimized to minimize geometric harmonics and reduce the conductor peak field in the end region, resulting in an expected short sample dipole field of 15 T. The support structure is composed by an external aluminum shell pre- tensioned with pressurized bladders and interference keys, and by two stainless steel end plates compressing the coil ends through four aluminum axial rods. We report on magnet design, assembly, and test results, including training performance, quench locations, and strain gauge measurements pressurized bladders. Figure 1: HD2 cross-section (left) and coil end support system (right) The coil has a straight section of about 481 mm and it tilts up (flares) at a 10 o angle in both ends through hard- way bends. After the hard-way bends, the flared region features a short straight section. The tilted ends are supported vertically by aluminum-bronze wedges surrounding the bore tube and axially by two end-plates pushed against the coil by four aluminum rods (Fig. 1, right). INTRODUCTION The Superconducting Magnet Program at Lawrence Berkeley National Laboratory (LBNL) is continuing the development of Nb 3 Sn high field magnets for the next generation of HEP colliders. The superconducting dipole HD2, recently fabricated and tested at the LBNL test facility, represents the first application of block-type coils to accelerator-quality dipole magnets. The conceptual design of the magnet was described in [1], whereas the mechanical analysis of the structure and the magnet fabrication were respectively reported in [2] and [3]. In this paper, after a brief overview of the magnet design and parameters, we present the results of two magnet tests, including strain gauge measurements (recorded during assembly, cool-down and excitation), training curve and quench locations. CONDUCTOR AND MAGNET PARAMETERS The two coil modules of HD2 are composed of two layers wound from a continuous length of cable made of 51 RRP strands with a 0.8 mm diameter. The cable is 22.008 mm wide and 1.401 mm thick. Three coils were fabricated: assuming strand properties from coil 1 (Fig. 2), the magnet has a maximum bore field of 15.1 T (4.2 K), with a conductor peak field of 15.9 T at a current of 17.4 kA. Coil 2 and 3 feature a short sample peak field about 0.6 T higher than coil 1. 10/17/07 - Brl-L22 - RW 9/21/07 - Brl-446 - RW 10/16/07 - XS-8 MAGNET DESIGN The HD2 magnet design (Fig. 1, left) features two block-type coils wound around a titanium alloy (Ti 6Al- 4V) pole. The pole includes a round cutout to provide room for a 3.65 mm thick stainless steel (Nitronic 40) bore tube with a clear aperture of 36 mm. The coils are supported by horizontal and vertical pads. Vertical pushers and horizontal rails transfer the load from the pads to the coils. Two yoke halves, made of 50 mm thick iron laminations, and a 41 mm thick aluminum shell provide the external coil pre-load through vertical and horizontal interference keys. The diameter of the cold mass is 705 mm. The structure is pre-loaded with water Strand critical current [ A ] 10/17/07 - XS-10 10/16/07 - XS-11 Parametrization RW at 4.2 K Parametrization XS at 4.2 K Parameterization XS at 4.5 K Parameterization XS at 1.9 K Loadline layer 2 peak field Total magnetic field [ T ] *Work supported by the U.S. D0E (No. DE-AC02-05CH11231) pferracin@lbl.gov Figure 2: Critical current (A) vs. applied field (T) measurements and parameterization curves of virgin