S. Prestemon

Design and performance of an eight-pole resistive magnet for soft x-ray magnetic dichroism measurements

To take full advantage of the strengths of soft x-ray magnetic dichroism (XMD) measurements for the detailed and quantitative characterization of multi-element magnetic materials, we developed an eight pole electromagnet that provides magnetic fields up to 0.9 T in any direction relative to the incoming x-ray beam. The setup allows us to measure magnetic circular and linear dichroism spectra as well as to thoroughly study magnetization reversal processes with very high precision. Design constraints and system optimization for maximum peak field are discussed. The predicted current-field relation is in excellent agreement with experimental findings. A brief discussion of the key technical difficulties in developing a similar superconducting device with peak fields of 5 T and ramping rates suitable for point-by-point full field reversal in an XMD experiment is presented.

Design of HQ—A High Field Large Bore

In support of the Large Hadron Collider luminosity upgrade, a large bore (120 mm) Nb3Sn 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 Nb3Sn technology with respect to the requirements of the luminosity upgrade at the LHC.

{\rm Nb}_{3}{\rm Sn}

In December 2009 during its first cold test, LQS01, the first Long Nb3Sn Quadrupole made by LARP (LHC Accelerator Research Program, a collaboration of BNL, FNAL, LBNL and SLAC), reached its target field gradient of 200 T/m. This target was set in 2005 by the US Department of Energy, CERN and LARP, as a significant milestone toward the development of Nb3Sn quadrupoles for possible use in LHC luminosity upgrades. LQS01 is a 90 mm aperture, 3.7 m long quadrupole using Nb3Sn coils. The coil layout is equal to the layout used in the LARP Technological Quadrupoles (TQC and TQS models). Pre-stress and support are provided by a segmented aluminum shell pre-loaded using bladders and keys, similarly to the TQS models. After the first test the magnet was disassembled, reassembled with an optimized pre-stress, and reached 222 T/m at 4.5 K. In this paper we present the results of both tests and the next steps of the Long Quadrupole R&D.

Quadrupole Magnet for LARP

An improved model for the strain dependence of the superconducting properties of Nb 3 Sn D Arbelaez 1,2 , A Godeke 1 and S O Prestemon 1 Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, CA 94720 University of California, Berkeley, CA 94720 E-mail: darbelaez@lbl.gov, agodeke@lbl.gov Abstract. We propose an improved model for the strain dependence of the superconducting properties of Nb 3 Sn. The model is based on the three dimensional strain tensor and derived in terms of the first, second and third invariants, and improves an existing model that only includes the second invariant. The axial form of the new model accurately accounts for the experimentally observed dependence of the effective upper critical magnetic field (H c2 ) on axial strain, i.e. a quasi-parabolic strain dependence, asymmetry, and an upturn at large compressive axial strain. An accurate model that accounts for the three dimensional nature of strain is important for scaling relations for the critical current that are used to model magnet performance based on wire measurements. PACS numbers: 74.25.Dw, 74.25.Ld, 74.70.Ad Submitted to: Supercond. Sci. Technol.

Test Results of the First 3.7 m Long Nb3Sn Quadrupole by LARP and Future Plans

The U.S. LHC Accelerator Research Program (LARP) has started the fabrication of 3.7-m long Nb3Sn quadrupole models. The Long Quadrupoles (LQ) are ldquoProof-of-Principlerdquo magnets which are to demonstrate that Nb3Sn technology is mature for use in high energy particle accelerators. Their design is based on the LARP Technological Quadrupole (TQ) models, developed at FNAL and LBNL, which have design gradients higher than 200 T/m and an aperture of 90 mm. The plans for the LQ R&D and a design update are presented and discussed in this paper. The challenges of fabricating long accelerator-quality Nb3Sn coils are presented together with the solutions adopted for the LQ coils (based on the TQ experience). During the fabrication and inspection of practice coils some problems were found and corrected. The fabrication at BNL and FNAL of the set of coils for the first Long Quadrupole is in progress.

An improved model for the strain dependence of the superconducting properties of Nb3Sn

The 3.7 m long quadrupole magnet LQS01 represents a major step of the US LHC Accelerator Research Program (LARP) towards the development of long Nb3Sn accelerator quadrupole magnets for a LHC Luminosity upgrade. The magnet support structure is a scale up of the 1 m long Technology Quadrupole TQS design with some modifications suggested by TQS model test results. It includes an aluminum shell pre-tensioned over iron yokes using pressurized bladders and locking keys (bladder and key technology). The axial support is provided by two stainless steel end plates compressed against the coil ends by four stainless steel rods. The structure, instrumented with strain gauges, has been fabricated and assembled around four aluminum ldquodummy coilsrdquo to determine pre-load homogeneity and mechanical characteristics during cool-down. After presenting the main magnetic and mechanical parameters of LQS01, we report in this paper on the design, assembly, and test of the support structure, with a comparison between strain gauges data and 3D finite element model results.

Development and Coil Fabrication for the LARP 3.7-m Long Nb3Sn Quadrupole

An R&D effort is underway at Lawrence Berkeley National Laboratory (LBNL) to develop the technology of Nb/sub 3/Sn superconducting undulators (SCUs). Issues relating to the selection of the appropriate conductor are discussed. The design and fabrication of SCUs using Nb/sub 3/Sn is presented. Two prototype devices have been designed and fabricated at LBNL. The first device concentrated on basic fabrication issues and on magnet protection, a key concern due to extremely high copper current densities during a quench. Test on the first prototype demonstrated that such devices can be passively protected in a scalable manner. The second device incorporated design improvements as well as trim coils that are designed to serve as the basic element of a future active phase error correction approach. Preliminary tests on the second device are presented. The trim coils were successfully tested at a variety of field levels. Two quench runs were performed, both occurring at /spl sim/70% of short-sample J/sub c/. Stability issues associated with flux-jumps and possible epoxy cracking are discussed.

Fabrication and Test of a 3.7 m Long Support Structure for the LARP

Canted-Cosine-Theta (CCT) magnet is an accelerator magnet that superposes fields of nested and tilted solenoids that are oppositely canted. The current distribution of any canted layer generates a pure harmonic field as well as a solenoid field that can be cancelled with a similar but oppositely canted layer. The concept places windings within mandrels ribs and spars that simultaneously intercept and guide Lorentz forces of each turn to prevent stress accumulation. With respect to other designs, the need for pre-stress in this concept is reduced by an order of magnitude making it highly compatible with the use of strain sensitive superconductors such as Nb3Sn or HTS. Intercepting large Lorentz forces is of particular interest in magnets with large bores and high field accelerator magnets like the one foreseen in the future high energy upgrade of the LHC. This paper describes the CCT concept and reports on the construction of CCT1 a “proof of principle” dipole.

{\hbox{Nb}}_{3}{\hbox{Sn}}

Lawrence Berkeley National Laboratory develops high-field Nb3Sn magnets for HEP applications. In the past few years, this experience has been extended to the design and fabrication of undulator magnets. Some undulator applications require devices that can operate in the presence of a heat load from a beam. The use of Nb3Sn permits operation of a device at both a marginally higher temperature (5-8 K) and a higher Jc, compared to NbTi devices, without requiring a larger magnetic gap. A half-undulator device consisting of 6 periods (12 coil packs) of 14.5 mm period was designed, wound, reacted, potted and tested. It reached the short sample current limit of 717 A in 4 quenches. The non-Cu Jc of the strand was over 7,600 A /mm2 and the Cu current density at quench was over 8,000 A/mm2 . Magnetic field models show that if a complete device was fabricated with the same parameters one could obtain beam fields of 1.1 T and 1.6 T for pole gaps of 8 mm and 6 mm, respectively.

Quadrupole Magnet LQS01

This paper presents a recently developed Code for Heater Delay Analysis (CoHDA), which is a tool for modeling protection heater induced quenches in superconducting Nb3Sn high-field accelerator magnets. The CoHDA thermal model numerically computes the heat diffusion from the heater to the coil and estimates the time delay to quench initiation by comparing the coil temperature with its critical surface. The model takes into account heater geometry, power, and various insulation layers and coil properties. Computational heater delays are compared with experimental data from the U.S. Large Hadron Collider Accelerator Research Program Nb3Sn High-Gradient Quadrupole magnet with good agreement. Based on the results, CoHDA provides a useful tool for quench protection design in impregnated magnets.