RRP Nb3Sn strand studies for LARP

The Nb{sub 3}Sn strand chosen for the next step in the magnet R&D of the U.S. LHC Accelerator Research Program is the 54/61 sub-element Restacked Rod Process by Oxford Instruments, Superconducting Technology. To ensure that the 0.7 mm RRP strands to be used in the upcoming LARP magnets are suitable, extensive studies were performed. Measurements included the critical current, {sub e}, using the voltage-current (V-I) method, the stability current, I{sub S}, as the minimal quench current obtained with the voltage-field (V-H) method, and RRR. Magnetization was measured at low and high fields to determine the effective filament size and to detect flux jumps. Effects of heat treatment temperature and durations on I{sub e} and I{sub S} were also studied. Using strand billet qualification and tests of strands extracted from cables, the short sample limits of magnet performance were obtained. The details and the results of this investigation are herein described

Development of Wind-and-React Bi-2212 Accelerator Magnet Technology

We report on the progress in our R&D program, targeted to develop the technology for the application of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (Bi-2212) in accelerator magnets. The program uses subscale coils, wound from insulated cables, to study suitable materials, heat treatment homogeneity, stability, and effects of magnetic field and thermal and electro-magnetic loads. We have addressed material and reaction related issues and report on the fabrication, heat treatment, and analysis of subscale Bi-2212 coils. Such coils can carry a current on the order of 5000 A and generate, in various support structures, magnetic fields from 2.6 to 9.9 T. Successful coils are therefore targeted towards a hybrid Nb{sub 3}Sn-HTS magnet which will demonstrate the feasibility of Bi-2212 for accelerator magnets, and open a new magnetic field realm, beyond what is achievable with Nb{sub 3}Sn

Mechanical Analysis of the Nb3Sn Dipole Magnet HD1

The Superconducting Magnet Group at Lawrence Berkeley National Laboratory (LBNL) has recently fabricated and tested HD1, a Nb3Sn dipole magnet. The magnet reached a 16 T field, and exhibited training quenches in the end regions and in the straight section. After the test, HD1 was disassembled and inspected, and a detailed 3D finite element mechanical analysis was done to investigate for possible quench triggers. The study led to minor modifications to mechanical structure and assembly procedure, which were verified in a second test (HD1b). This paper presents the results of the mechanical analysis, including strain gauge measurements and coil visual inspection. The adjustments implemented in the magnet structure are reported and their effect on magnet training discussed

Design and Test of a Nb3Sn Subscale Dipole Magnet for Training Studies

As part of a collaboration between CEA/Saclay and the Superconducting Magnet Group at LBNL, a subscale dipole structure has been developed to study training in Nb3Sn coils under variable pre-stress conditions. This design is derived from the LBNL Subscale Magnet and relies on the use of identical Nb{sub 3}Sn racetrack coils. Whereas the original LBNL subscale magnet was in a dual bore 'common-coil' configuration, the new subscale dipole magnet (SD) is assembled as a single bore dipole made of two superposed racetrack coils. The dipole is supported by a new mechanical structure developed to withstand the horizontal and axial Lorentz forces and capable of applying variable vertical, horizontal and axial preload. The magnet was tested at LBNL as part of a series of training studies aiming at understanding of the relation between pre-stress and magnet performance. Particular attention is given to the coil ends where the magnetic field peaks and stress conditions are the least understood. After a description of SD design, assembly, cool-down and tests results are reported and compared with the computations of the OPERA3D and ANSYS magnetic and mechanical models

Design and Fabrication of a Supporting Structure for 3.6m Long Nb3Sn Racetrack Coils

As part of the LHC Accelerator Research Program (LARP), three US national laboratories (BNL, FNAL, and LBNL) are currently engaged in the development of superconducting magnets for the LHC Interaction Regions (IR) beyond the current design. As a first step towards the development of long Nb{sub 3}Sn quadrupole magnets, a 3.6 m long structure, based on the LBNL Subscale Common-Coil Magnet design, will be fabricated, assembled, and tested with aluminum-plate 'dummy coils'. The structure features an aluminum shell pre-tensioned over iron yokes using pressurized bladders and locking keys (bladder and key technology). Pre-load homogeneity and mechanical responses are monitored with pressure sensitive films and strain gauges mounted on the aluminum shell and the dummy coils. The details of the design and fabrication are presented and discussed, and the expected mechanical behavior is analyzed with finite element models

Materials for Very High Field Dipole Magnets

No abstract prepared

Critical current variation as a function of transverse stress of Bi-2212 Rutherford cables

Transverse loading experiments on wire has shown that a significant drop in critical current occurs for stresses greater than 50 MPa. However, many high-energy physics applications require that the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} conductor withstand stresses greater than 100 MPa without permanent degradation. Therefore, a study of epoxy impregnated cables, identical to those used in accelerator magnet applications, has been performed. This work presents the first results of Rutherford cables of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} with transverse stress. The results show that the cable can withstand stresses up to 60 MPa with a strain of about 0.3 % for the face loading orientation and 100 MPa for the edge loading orientation

RRP Nb 3 Sn Strand Studies for LARP

Abstract-The Nb 3 Sn strand chosen for the next step in the magnet R&D of the U.S. LHC Accelerator Research Program is the 54/61 sub-element Restacked Rod Process by Oxford Instruments, Superconducting Technology. To ensure that the 0.7 mm RRP strands to be used in the upcoming LARP magnets are suitable, extensive studies were performed. Measurements included the critical current, , using the voltage-current ( ) method, the stability current, , as the minimal quench current obtained with the voltage-field ( ) method, and . Magnetization was measured at low and high fields to determine the effective filament size and to detect flux jumps. Effects of heat treatment temperature and durations on and were also studied. Using strand billet qualification and tests of strands extracted from cables, the short sample limits of magnet performance were obtained. The details and the results of this investigation are herein described. Index Terms-Critical current density, magnetic instability, Nb 3 Sn, restack rod process

Influence of Compaction during reaction Heat Treatment on the Interstrand Contact Resistances of Nb 3Sn Rutherford Cables for Accelerator Magnets

The high field superconducting magnets required for ongoing and planned upgrades to the Large Hadron Collider (LHC) will be wound with Nb 3Sn Rutherford cables for which reason studies of Nb 3Sn strand, cable, and magnet properties will continue to be needed. Of particular importance is field quality. The amplitudes of multipoles in the bore fields of dipole and quadrupole magnets, induced by ramp-rate-dependent coupling currents, are under the control of the interstrand contact resistances-crossing-strand, $R-{c}$, adjacent strand, $R-{a}$ , or a combination of them, $R-{{\text{eff}}}$. Although two decades ago it was agreed that for the LHC $R-{c}$ should be in the range 10-30 μ, more recent measurements of LHC quadrupoles have revealed $R-{c}$ values ranging from 95 to 230 μ. This paper discusses ways in which these values can be achieved. In a heavily compacted cable $R-{{\text{eff}}}$ can be tuned to some predictable value by varying the width of an included stainless steel (effectively 'insulating') core. But cables are no longer heavily compacted with the result that the crossing strands of the impregnated cable are separated by a thick epoxy layer that behaves like an insulating core. If a stainless steel core is actually present, $R-{{\text{eff}}}$ must be independent of core width. Since there is no guarantee that a fixed predetermined amount of interlayer separation could be reproduced from winding to winding it would be advisable to include a full width core