S. Mattafirri

Magnet RaD for the US LHC Accelerator Research Program (LARP)

TUA2OR6 Magnet RD fax: 510-486-5310; e-mail: sagourlay@lbl.gov). G. Ambrosio, N. Andreev, E. Barzi, R. Bossert, V. S. Kashikhin, V. V. Kashikhin, F. Nobrega, I. Novitsky, D. Turrioni, R. Yamada, and A.V. Zlobin are with Fermilab National Accelerator Laboratory, Batavia, IL 3 M. Anerella, A. Ghosh , , R. Gupta, M. Harrison, J. Schmazle, and P. Wanderer are with Brookhaven National Laboratory, Upton, NY.

Correlation between strand stability and magnet performance

Magnet programs at BNL, LBNL and FNAL have observed instabilities in high J/sub c/ Nb/sub 3/Sn strands and magnets made from these strands. This paper correlates the strand stability determined from a short sample-strand test to the observed magnet performance. It has been observed that strands that carry high currents at high fields (greater than 10 T) cannot sustain these same currents at low fields (1-3 T) when the sample current is fixed and the magnetic field is ramped. This suggests that the present generation of strand is susceptible to flux jumps (FJ). To prevent flux jumps from limiting stand performance, one must accommodate the energy released during a flux jump. To better understand FJ this work has focused on wire with a given sub-element diameter and shows that one can significantly improve stability by increasing the copper conductivity (higher residual resistivity ratio, RRR, of the Cu). This increased stability significantly improves the conductor performance and permits it to carry more current.

Design of HD2: a 15 tesla Nb/sub 3/Sn dipole with a 35 mm bore

The Nb/sub 3/Sn dipole HD1, recently fabricated and tested at LBNL, pushes the limits of accelerator magnet technology into the 16 T field range, and opens the way to a new generation of HEP colliders. HD1 is based on a flat racetrack coil configuration and has a 10 mm bore. These features are consistent with the HD1 goals: exploring the Nb/sub 3/Sn conductor performance limits at the maximum fields and under high stress. However, in order to further develop the block-coil geometry for future high-field accelerators, the bore size has to be increased to 30-50 mm. With respect to HD1, the main R&D challenges are: (a) design of the coil ends, to allow a magnetically efficient cross-section without obstructing the beam path; (b) design of the bore, to support the coil against the pre-load force; (c) correction of the geometric field errors. HD2 represents a first step in addressing these issues, with a central dipole field above 15 T, a 35 mm bore, and nominal field harmonics within a fraction of one unit. This paper describes the HD2 magnet design concept and its main features, as well as further steps required to develop a cost-effective block-coil design for future high-field, accelerator-quality dipoles.

Development of TQC01, a 90 mm

As a first step toward the development of a large-aperture Nb3Sn superconducting quadrupole for the Large Hadron Collider (LHC) luminosity upgrade, two-layer technological quadrupole models (TQS01 at LBNL and TQC01 at Fermilab) are being constructed within the framework of the US LHC Accelerator Research Program (LARP). Both models use the same coil design, but have different coil support structures. This paper describes the TQC01 design, fabrication technology and summarizes its main parameters

hboxNb_3hbox Sn

The Lawrence Berkeley National Laboratory (LBNL) Superconducting Magnet Group has completed the design, fabrication and test of HD1, a 16 T block-coil dipole magnet. State of the art Nb/sub 3/Sn conductor was wound in double-layer racetrack coils and supported by an iron yoke and a tensioned aluminum shell. In order to prevent conductor movement under magnetic forces up to the design field, a coil pre-stress of 150 MPa was required. To achieve this level without damaging the brittle conductor, the target stress was generated during cool-down to 4.2 K by exploiting the thermal contraction differentials between yoke and shell. Accurate control of the shell tension during assembly was obtained using pressurized bladders and interference load keys. An integrated 3D CAD model was used to optimize magnetic and mechanical design and analysis.

Model Quadrupole for LHC Upgrade Based on SS Collar

The U.S. LHC Accelerator Research Program (LARP), a collaboration between BNL, FNAL, LBNL, and SLAC, has among its major objectives the development of advanced magnet technology for an LHC luminosity upgrade. The LBNL Superconducting Magnet Group supports this program with a broad effort involving design studies, Nb/sub 3/Sn conductor development, mechanical models, and basic prototypes. This paper describes the development of a large aperture Nb/sub 3/Sn racetrack quadrupole magnet using four racetrack coils from the LBNL Subscale Magnet (SM) Program. The magnet provides a gradient of 95 T/m in a 110 mm bore, with a peak field in the conductor of 11.2 T. The coils are pre-stressed by a mechanical structure based on a pre-tensioned aluminum shell, and axially supported with aluminum rods. The mechanical behavior has been monitored with strain gauges and the magnetic field has been measured. Results of the test are reported and analyzed.

HD1: design and fabrication of a 16 Tesla Nb/sub 3/Sn dipole magnet

After the fabrication and test of HD1, a 16 T Nb3Sn dipole magnet based on flat racetrack coil configuration, the Superconducting Magnet Program at Lawrence Berkeley National Laboratory (LBNL) is developing the Nb3Sn dipole HD2. With a dipole field above 15 T, a 35 mm clear bore, and nominal field harmonics within a fraction of one unit, HD2 represents a further step towards the application of block-type coils to high-field accelerator magnets. The design features tilted racetrack-type ends, to avoid obstructing the beam path, and a 4 mm thick stainless steel tube, to support the coil during the pre-loading operation. The mechanical structure, similar to the one used for HD1, is based on an external aluminum shell pre-tensioned with pressurized bladders. Axial rods and stainless steel plates provide longitudinal support to the coil ends during magnet excitation. A 3D finite element analysis has been performed to evaluate stresses and deformations from assembly to excitation, with particular emphasis on conductor displacements due to Lorentz forces. Numerical results are presented and discussed

Development of a large aperture Nb/sub 3/Sn racetrack quadrupole magnet

Nb/sub 3/Sn is the superconductor most used in the R&D of high field accelerator magnets by either the wind&react or the react&wind technique. In order to program the low temperature steps of the heat treatment, the growth kinetics of Cu-Sn intermetallics was investigated as a function of duration and temperature. The diffusion constants of /spl eta/, /spl epsiv/ and /spl delta/ phases between 150 /spl deg/C and 550 /spl deg/C were evaluated using Cu-Sn model samples. For an accurate data analysis, statistical and systematic errors were determined. Next the behavior of Internal Tin and Modified Jelly Roll Nb/sub 3/Sn composites was compared with the model predictions.

Mechanical Design of HD2, a 15 T

The US LHC Accelerator Research Program (LARP) consists of four US laboratories (BNL, FNAL, LBNL, and SLAC) collaborating with CERN to achieve a successful commissioning of the LHC and to develop the next generation of Interaction Region magnets. In 2004, a large aperture Nb 3Sn racetrack quadrupole magnet (SQ01) has been fabricated and tested at LBNL. The magnet utilized four subscale racetrack coils and was instrumented with strain gauges on the support structure and directly over the coils turns. SQ01 exhibited training quenches in two of the four coils and reached a peak field in the conductor of 10.4 T at a current of 10.6 kA. After the test, the magnet was disassembled, inspected with pressure indicating films, and reassembled with minor modifications. A second test (SQ01b) was performed at FNAL and included training studies, strain gauge measurements and magnetic measurements. Magnet inspection, test results, and magnetic measurements are reported and discussed, and a comparison between strain gauge measurements and 3D finite element computations is presented

hboxNb_3hboxSn

The layer growth and superconducting properties of Nb/sub 3/Sn are investigated as a function of the heat treatment (HT) duration and temperature for internal tin and powder-in-tube strands at 650 /spl deg/C, 700 /spl deg/C and 750 /spl deg/C. For all times and temperatures, the Nb/sub 3/Sn layer thickness is measured, the critical current at 4.2 K is tested as a function of magnetic field, and the upper critical field is obtained through parameterization. Results of the layer critical current density are also shown as a function of HT duration and temperature.