Quench Propagation Velocity and Hot Spot Temperature Models in Nb3Sn Racetrack Coils (original) (raw)
Related papers
Quench Analysis of High Current Density Nb3Sn Conductors in Racetrack Coil Configuration
IEEE Transactions on Applied Superconductivity, 2015
The luminosity upgrade of the Large Hadron Collider (HL-LHC) requires the development of new type of superconducting cables based on advanced Nb3Sn strands. In the framework of the FP7 European project EUCARD the cables foreseen for the HL-LHC project have been tested recently in a simplified racetrack coil configuration, the so-called Short Model Coil (SMC). In 2013 to 2014, two SMCs wound with 40-strand (RRP 108/127) cables, with different heat treatment processes, reached during training at 1.9 K a current and peak magnetic field of 15.9 kA, 13.9T,and 14.3 kA, 12.7 Trespectively. Using the measured signals from the voltage taps, the behavior of the quenches is analyzed in terms of transverse and longitudinal propagation velocity and hot spot temperature. These measurements are compared with both analytical and numerical calculations from adiabatic models.The coherence of the results from the presented independent methods helps in estimating the relevance of the material properties and the adiabatic assumption for impregnated Nb3Sn conductor modelling.
Advanced Nb3Sn Conductors Tested in Racetrack Coil Configuration for the 11T Dipole Project
IEEE Transactions on Applied Superconductivity, 2018
Within the 11T dipole magnet conductor development for the high-luminosity LHC upgrade, two types of Nb 3 Sn cable based on the powder-in-tube (PIT) and the Rod and Restack processes (RRP) are tested in racetrack configuration in the short model coil (SMC) magnets. In 2016 and 2017, the performances of three different coils wound with 40-strand cables, one made of OST RRP 132/169 and two of PIT 120 strands have been measured using the SMC structure. This paper reports on the main design parameters of the SMC-11T-3 (RRP), and the SMC-11T-4 and SMC-11T-5 (PIT) magnets including details on the instrumentation, applied preload, maximum expected performances, residual resistivity ratio, splice resistances, and inductances. For SMC-11T-3, eight consecutive runs have been performed varying the azimuthal prestress from 150 to 200 MPa with the aim to study the impact of the transverse pressure on the magnet stability and degradation. Only two runs were done for SMC-11T-4 and SMC-11T-5. For the three magnets, the training behavior at both 4.2 and 1.9 K is analyzed in terms of training rate, quench location, maximum quench current and its dependence to the helium bath temperature, the level of transverse prestress, and current ramp rate. The main outcome of the tests on the coil performance is given as conclusion. Index Terms-High luminosity LHC, high field Nb 3 Sn magnets, superconducting coils racetrack.
IEEE Transactions on Applied Superconductivity, 2016
The High-Luminosity upgrade of the Large Hadron Collider at CERN comprises the implementation of a new generation of high-field superconducting quadrupole and dipole magnets. The dipole fields of up to 12.1 T at nominal current require the use of high-critical-current Nb 3 Sn strand for the fabrication of the coils. These coils will be up to 8 m long and represent the longest Nb 3 Sn coils so far fabricated for operation accelerator magnets. This brittle A15 phase material requires coil winding prior formation of the superconducting material. The development program at CERN includes the construction of 2-m-long models and full-length prototypes by the wind-and-react technique. The process time and temperature uniformity are stringent during heat treatment and performed inside an EN 1.4841 (AISI Type 314) stainless-steel retort furnace with turbulent flow of Ar atmosphere. During the process, the coil is supported inside a reaction fixture made from 316LN. This paper presents temperature uniformity measurements and results from numerical simulations. The goal is to further improve the heat transfer in combination with turbulent flow generated by a ventilation system. This allows optimizing control parameters for improved heat performance during both the ramping and the dwell time. Index Terms-LHC upgrade, Nb 3 Sn magnet, reaction heat treatment, superconducting accelerator magnets. I. INTRODUCTION T HE High Luminosity LHC upgrades target is to increase the integrated luminosity by a factor 10, resulting in an integrated luminosity of 3000 fb −1. Several modifications on the existing superconducting magnets will allow reaching this target. One major improvement foreseen is the reduction of the beam size at the collision points. This requires the development of 150 mm single aperture quadrupoles in the interaction regions. These quadrupoles are under development in a joint collaboration between CERN and the US-LHC Accelerator Research Program (LARP). The chosen approach for achieving Manuscript
—The high field superconducting magnets required for ongoing and planned upgrades to the large hadron collider (LHC) will be wound with Nb3Sn Rutherford cables for which reason studies of Nb3Sn 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, Rc, adjacent strand, Ra, or a combination of them, Reff. Although two decades ago it was agreed that for the LHC Rc should be in the range 10-30 μΩ more recent measurements of LHC quadrupoles have revealed Rc values ranging from 95 μΩ to 230 μΩ. The present paper discusses ways in which these values can be achieved. In a heavily compacted cable Reff 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 which behaves like an insulating core. If a stainless steel core is actually present Reff 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. Index Terms— Nb3Sn accelerator magnets, Nb3Sn Rutherford cables, Nb3Sn strands, interstrand contact resistance.
Superconductor Science and Technology, 2020
In the frame of the High-Luminosity Large Hadron Collider construction and Future Circular Collider development program, the magnetic field in the accelerator dipole magnets is being enhanced to 11 T, and 15 T to 16 T level, respectively. Advanced Nb3Sn superconductors with a non-copper critical current density exceeding 2500 A mm−2 at 4.2 K and 12 T, are being developed using the Restacked-Rod-Process (RRP) and Powder-In-Tube (PIT) wire technologies. However, since Nb3Sn is extremely brittle, it is a significant challenge to construct the high-field dipole magnets with such very strain-susceptible superconductor. The high-level of stress acting on the wide face of the Rutherford cables in the coils of 120 MPa to 200 MPa generated by the Lorenz’ force, causes initially a reversible reduction and eventually at some stress level followed by permanent degradation of the critical current when strain goes to high. This study sets out to examine the critical current and upper critical fie...
IEEE Transactions on Applied Superconductivity, 2018
The knowledge of the temperature induced changes of the superconductor volume, and of the thermomechanical behavior of the different coil and tooling materials is required for predicting the coil geometry and the stress distribution in the coil after the Nb3Sn reaction heat treatment. In the present study we have measured the Young's and shear moduli of the HL-LHC 11 T Nb3Sn dipole magnet coil and reaction tool constituents during in situ heat cycles with the dynamic resonance method. The thermal expansion behaviors of the coil components and of a free standing Nb3Sn wire were compared based on dilation experiments.
AIP Conference Proceedings
A 10 T racetrack magnet (HFDB-03) wound with pre-reacted Nb 3 Sn Rutherford cable has been fabricated and tested at Fermilab. This magnet is the third one in a proof-ofprinciple series for the use of the React-and-Wind technology in common-coil dipole magnets for future accelerators. It consists of two flat racetrack coils (28 turns each) separated by 5 mm. The maximum field on the coil, at the short sample limit of 16530 A, is 10 tesla. The cable has 41 strands with 0.7 mm diameter and the minimum bend radius in the magnet ends is 90 mm. The predecessor of this magnet (HFDB-02) reached 78 % of the short sample limit at 7.7 T. The mechanical design was improved and the fabrication procedure was slightly modified in order to address possible causes of limitation. In this paper we present the mechanical design and analysis of HFDB-03, the modifications to the fabrication procedure and the test results.
Fabrication and test of a racetrack magnet using pre-reacted Nb3Sn cable
2002
A racetrack magnet, using Nb 3 Sn superconducting cable reacted before winding, has been fabricated and tested at Fermilab. It consists of two flat racetrack coils, connected in a common-coil configuration, separated by a 5 mm thick fiberglass plate. Synthetic oil was used to prevent sintering of the strands during the heat treatment. The coils were wound and vacuum impregnated in the mechanical structure. The turn-to-turn insulation, consisting of Kapton and pre-impregnated fiberglass tapes as wide as the cable, was wound together with the bare cable in order to form a continuous inter-turn spacer. The coils were instrumented with voltage taps, temperature sensors, spot heaters and quench heaters. The maximum current achieved was 12675 A which is 78% of the short sample limit at 5.1 K (minimum temperature in the coil during 75 A/s ramp). Measurement of the temperature margin revealed a low degradation in the innermost turns. Quench performances at different temperatures and ramp rate effects have been measured and are presented and discussed.