Rutherford Cable Research Articles

Critical currents of Rutherford MgB2 cables compacted by two-axial rolling

Two types of Rutherford cables made of two strand layers of commercial MgB2 wires manufactured by Hyper Tech Research, Inc. have been made. Flat rectangular cables consisting of 12 single-core MgB2/Nb/Cu10Ni, or 6-filaments MgB2/Nb/Cu strands, both of diameter 390 mewm, were assembled using a back-twist cabling machine with transposition length of 20 mm. In order to analyze impact of the cable compaction on critical currents, cables were two-axially rolled, each by a single step reduction of 3.5%−29.7% to thickness range of 0.775−0.62 mm. It was found that by increasing the packing factor (PF) of cable above 0.79, the critical current begins to increase. It is improved nearly two times up to the PF limit 0.89. Compaction over the PF limit introduced cable degradation and decrease of critical current. Bending tests applied to cables showed that critical current degradation starts below the bending diameter 120 mm for 6-filaments Cu sheath and 70 mm for single-core Cu10Ni sheath cable. Tensile tests showed similar irreversible strain values for the both types of cables. Rutherford cables assembled of single-core strands are promising for low field (2.7−4 T) applications where low bending diameters are required.

Braiding ultrathin layer for insulation of superconducting Rutherford cables

Over-braiding of superconducting Rutherford cable was used for the composite insulation in this research. Braiding was a suitable alternative to fabric tape winding for achieving ultrathin insulation with required electrical breakdown voltage. A brief overview of the superconducting magnets, their application and requirements of insulation has been covered in order to bridge the literature gap between braiding and the superconducting magnet field of studies. Organic size coating on the fibre leaves carbon residue during high temperature treatment of the cables and hence glass fibre was desized before braiding. Braiding difficulties with desized glass fibre and possibility of braiding using compatible size coating have been discussed. The requirement of ultrathin braided layer was achieved with sufficient surface coverage with a suitable braid angle and fibre. As part of the study, braid cover factor variation on the surface of the cable was investigated and it was discussed using image analysis.

Simulation of the cabling process for Rutherford cables: An advanced finite element model

In all existing large particle accelerators (Tevatron, HERA, RHIC, LHC) the main superconducting magnets are based on Rutherford cables, which are characterized by having: strands fully transposed with respect to the magnetic field, a significant compaction that assures a large engineering critical current density and a geometry that allows efficient winding of the coils. The Nb3Sn magnets developed in the framework of the HL-LHC project for improving the luminosity of the Large Hadron Collider (LHC) are also based on Rutherford cables. Due to the characteristics of Nb3Sn wires, the cabling process has become a crucial step in the magnet manufacturing. During cabling the wires experience large plastic deformations that strongly modify the geometrical dimensions of the sub-elements constituting the superconducting strand. These deformations are particularly severe on the cable edges and can result in a significant reduction of the cable critical current as well as of the Residual Resistivity Ratio (RRR) of the stabilizing copper. In order to understand the main parameters that rule the cabling process and their impact on the cable performance, CERN has developed a 3D Finite Element (FE) model based on the LS-Dyna® software that simulates the whole cabling process. In the paper the model is presented together with a comparison between experimental and numerical results for a copper cable produced at CERN.

Dimensional Changes of Nb3Sn Rutherford Cables During Heat Treatment

In high field magnet applications, Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coils undergo a heat treatment step after winding. During this stage, coils radially expand and longitudinally contract due to the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn phase change. In order to prevent residual strain from altering superconducting performances, the tooling must provide the adequate space for these dimensional changes. The aim of this paper is to understand the behavior of cable dimensions during heat treatment and to provide estimates of the space to be accommodated in the tooling for coil expansion and contraction. This paper summarizes measurements of dimensional changes on strands, single Rutherford cables, cable stacks, and coils performed between 2013 and 2015. These samples and coils have been performed within a collaboration between CERN and the U.S. LHC Accelerator Research Program to develop Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn quadrupole magnets for the HiLumi LHC. The results are also compared with other high field magnet projects.

Retraining of the 1232 Main Dipole Magnets in the LHC

The Large Hadron Collider (LHC) contains eight main dipole circuits, each of them with 154 dipole magnets powered in series. These 15-m-long magnets are wound from Nb-Ti superconducting Rutherford cables, and have active quench detection triggering heaters to quickly force the transition of the coil to the normal conducting state in case of a quench, and hence reduce the hot spot temperature. During the reception tests in 2002-2007, all these magnets have been trained up to at least 12 kA, corresponding to a beam energy of 7.1 TeV. After installation in the accelerator, the circuits have been operated at reduced currents of up to 6.8 kA, from 2010 to 2013, corresponding to a beam energy of 4 TeV. After the first long shutdown of 2013-2014, the LHC runs at 6.5 TeV, requiring a dipole magnet current of 11.0 kA. A significant number of training quenches were needed to bring the 1232 magnets up to this current. In this paper, the circuit behavior in case of a quench is presented, as well as the quench training as compared to the initial training during the reception tests of the individual magnets.

Geometrical Behavior of Nb3Sn Rutherford Cables During Heat Treatment

Geometrical Behavior of Nb₃Sn Rutherford Cables During Heat Treatment

Transport Properties of CuNb/Nb3Sn Rutherford Coils With Various Diameters

Our group has been developing an Nb-rod-processed CuNb-reinforced Nb3Sn Rutherford cable for developments in high-field superconducting magnets, such as a 25-T cryogen-free superconducting magnet. The Rutherford cable has good mechanical, electrical, and superconducting properties in high fields. In this paper, we investigated the influence of winding coil diameters on the transport properties of the Rutherford cable for the coil application wound with a react-and-wind method. We prepared two Rutherford coils with diameters of 110 mm (0.2% pure bending strain) and 70 mm (0.6% pure bending strain) with 0.7% prebending treatment in order to measure the critical current at various temperatures in fields up to 18 T. We found that the Rutherford coil with a diameter of 110 mm has good transport properties. The critical current of the Rutherford coil with a diameter of 70 mm exhibited a deterioration of about 14% in comparison to the coil having a diameter of 110 mm. Although the tensile strain dependence of the critical current $(I_{c})$ suggests a large deterioration for the 0.6% pure bent coil, the Rutherford coil can keep the high $I_{c}$ under a large pure bending strain.

Nb3Sn RRP Strand and Rutherford Cable Development for a 15 T Dipole Demonstrator

Keystoned Rutherford cables made of 28 strands and with a stainless steel core were developed and manufactured using 1-mm $\text{Nb}_{3}\text{Sn}$ composite wires produced by Oxford Superconducting Technology with 127 and 169 restacks using the Restacked-Rod-Process. The performance and properties of these cables were studied to evaluate possible candidates for 15-T accelerator magnets.

Analysis of the quench propagation along Nb3Sn Rutherford cables with the THELMA code. Part II: Model predictions and comparison with experimental results

To improve the technology of the new generation of accelerator magnets, prototypes are being manufactured and tested in several laboratories. In parallel, many numerical analyses are being carried out to predict the magnets behaviour and interpret the experimental results. This paper focuses on the quench propagation velocity, which is a crucial parameter as regards the energy dissipation along the magnet conductor. The THELMA code, originally developed for cable-in-conduit conductors for fusion magnets, has been used to study such quench propagation. To this purpose, new code modules have been added to describe the Rutherford cable geometry, the material non-linear thermal properties and to describe the thermal conduction problem in transient regime. THELMA can describe the Rutherford cable at the strand level, modelling both the electrical and thermal contact resistances between strands and enabling the analysis of the effects of local hot spots and quench heaters. This paper describes the model application to a sample of Short Model Coil tested at CERN: a comparison is made between the experimental results and the model prediction, showing a good agreement. A comparison is also made with the prediction of the most common analytical models, which give large inaccuracies when dealing with low n-index cables like Nb3Sn cables.

Analysis of the quench propagation along Nb3Sn Rutherford cables with the THELMA code. Part I: Geometric and thermal models

The paper describes the new lumped thermal model recently implemented in THELMA code for the coupled electromagnetic–thermal analysis of superconducting cables. A new geometrical model is also presented, which describes the Rutherford cables used for the accelerator magnets. A first validation of these models has been given by the analysis of the quench longitudinal propagation velocity in the Nb3Sn prototype coil SMC3, built and tested in the frame of the EUCARD project for the development of high field magnets for LHC machine. This paper shows in detail the models, while their application to the quench propagation analysis is presented in a companion paper.

Results of R&amp;D and Production on Two Types of High-Purity Aluminum-Stabilized Superconducting Cable

Two types of high-purity aluminum-stabilized superconducting conductor were developed and produced for use in large-aperture high-field superconducting solenoids. One (DS1) has transverse rectangular dimensions of 5.27 mm × 20.1 mm, whereas the other (PS) has 5.52 mm × 30.1 mm. The superconductor for both cables is copper-stabilized NbTi strand woven into a Rutherford cable. The stabilizer for the DS1 conductor is 5N aluminum, whereas the stabilizer for PS is an aluminum alloy of 5N aluminum with a 0.1wt% Ni addition. Continuous unit lengths up to 1700 m are required for production. In total, over 18 000 m are required for this contract. A major goal of the R&D is to produce a cable having high shear strength between Cu and Al boundary while maintaining high residual resistivity ratio (RRR) and strength in the Al parts. We report on the cable mechanical properties, RRR of aluminum, sharing stress between Cu and Al, and critical current $(I_{C})$ of the cable, as well as the progress toward the fabrication of long unit lengths for production.

Development of Aluminum-Stabilized Superconducting Cables for the Mu2e Detector Solenoid

The Mu2e experiment at Fermilab is designed to measure the rare process of direct muon-to-electron conversion in the field of a nucleus. The experiment comprises a system of three superconducting solenoids, which focus secondary muons from the production target and transport them to an aluminum stopping target, while minimizing the associated background. The Detector Solenoid (DS) is the last magnet in the transport line and its main functions are to provide a graded field in the region of the stopping target as well as a precision magnetic field in a volume large enough to house the tracker downstream of the stopping target. The Detector Solenoid coils are designed to be wound using NbTi Rutherford cables conformed in high purity aluminum for stabilization and then cold-worked for strength. Two types of Al-stabilized conductor are required to build the DS coils, one for the gradient section and one for the spectrometer section of the solenoid. The dimensions are optimized to generate the required field profile when the same current is transported in both conductors. The conductors contain NbTi Rutherford cables with 12 (DS1) and 8 (DS2) strands respectively and are manufactured by two different vendors. This paper describes the results of themore » manufacturing of production lengths of the Al-stabilized cables needed to build the Mu2e Detector Solenoid as well as the testing campaigns and main results. The main cable properties and results of electrical and mechanical tests are summarized and discussed for each stage of the cable development process. Results are compared to design values to show how the production cables satisfy all the design criteria starting from the NbTi wires to the Al-stabilized cables.« less

Development of Nb-Rod-Method Cu–Nb Reinforced Nb3Sn Rutherford Cables for React-and-Wind Processed Wide-Bore High Magnetic Field Coils

We developed Cu-Nb reinforced Nb 3 Sn Rutherford cables for wide-bore high magnetic field coils that were able to be produced by React-and-Wind technique. The Cu-Nb/Nb 3 Sn strands were reinforced by internal Cu-20 vol%Nb composites fabricated by the Nb-rod-method and were manufactured through the bronze-process. The Rutherford cables composed of sixteen un-reacted Cu-Nb/Nb 3 Sn strands of 0.8-mm diameter were heat-treated at 670 °C for 96 hours. After that, repeated bending strains (pre-bending strains) were applied to the flatwise direction of the reacted Nb 3 Sn Rutherford cables at room temperature. Critical current (Ic) values of Cu-Nb/Nb 3 Sn strands extracted from the Rutherford cables were compared to those of the single strands that had undergone the same processing as the cables. I c values under the applied tensile stress of the Rutherford cable were increased by the pre-bending treatment as similar to the single strand. The performances of Cu-Nb/Nb 3 Sn Rutherford cables were improved by utilization of the pre-bending process.

Transport Properties of CuNb Reinforced &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\hbox{Nb}_{3}\hbox{Sn}$&lt;/tex-math&gt;&lt;/inline-formula&gt; Rutherford Coils in High Fields

Nb 3 Sn Rutherford cables have been investigated for the development of a 25-T cryogen-free superconducting magnet. We developed Rutherford cables composed of 16 Nb-rodprocessed CuNb-reinforced Nb 3 Sn (CuNb/Nb 3 Sn) strands with an 0.8-mm diameter. In this paper, the transport and mechanical properties of the epoxy impregnated multilayer coil of the (CuNb/Nb 3 Sn) Rutherford cable were investigated in high magnetic fields. The coil reached the maximum transport current of 1655 A at 4.2 K and 13.5 T after four times of training quenches. The electromagnetic stresses at the maximum transport current were 240 MPa at an inner surface of the coil and 210 MPa at an outer surface of the coil. The hoop strain of 0.2% for the coil was measured, which was applied at the outer surface of the coil. The strain value was the same as the calculated result using Wilson's equation and stress-strain curve of the strand.

Thermal-Mechanical Properties of Epoxy-Impregnated Bi-2212/Ag Composite

Knowledge of the thermal-mechanical properties of epoxy/superconductor/insulation composite is important for designing, fabricating, and operating epoxy impregnated high field superconducting magnets near their ultimate potentials. We report measurements of the modulus of elasticity, Poisson's ratio, and the coefficient of thermal contraction of epoxy-impregnated composite made from the state-of-the-art powder-in-tube multifilamentary Ag/Bi 2 Sr 2 CaCu 2 O x round wire at room temperature and cryogenic temperatures. Stress-strain curves of samples made from single-strand and Rutherford cables were tested under both monotonic and cyclic compressive loads, with single strands insulated using a thin TiO 2 insulation coating and the Rutherford cable insulated with a braided ceramic sleeve.

Analysis and Modeling of Damage in RRP Nb&lt;sub&gt;3&lt;/sub&gt;Sn Wires During Cabling

High-critical current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires such as restacked-rod process wires are used in Rutherford cables for high-field superconducting magnets. However, during cabling, the wires experience strong plastic strains, which break some superconducting sub-elements and can degrade the electromagnetic performances. The damage can be reduced by forming Cu-Sn phases in the sub-elements during an annealing process prior to cabling. We found experimentally that annealing plays a significant role in reducing damage. Furthermore, we used finite-element models to validate the observations on samples and quantify the impact of annealing on damage reduction.

Quench Propagation in &lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\hbox{Nb}_{3}\hbox{Sn} $&lt;/tex-math&gt;&lt;/inline-formula&gt; Rutherford Cables for the Hi-Lumi Quadrupole Magnets

The quadrupole magnets for the LHC High Luminosity (Hi-Lumi) upgrade will be based on Nb 3 Sn Rutherford cables that operate at 1.9 K and experience magnetic fields larger than 12 T. Because of the large stored energy, one of the major issues in the design of these magnets is their protection. To study the quench propagation in Nb 3 Sn Rutherford cables for the Hi-Lumi Quadrupole magnets, a campaign of measurements was carried out in the FRESCA test station at CERN. In addition to the critical and stability current measurements at 4.3 K and 1.9 K, we performed a series of tests where the quenches were induced by resistive heaters impregnated in the cable. The longitudinal and transversal speeds of the normal zone propagation were investigated at different magnetic fields and operating currents. In this paper, the numerical and experimental results are reported, compared and discussed.

Mechanically Reinforced Bi-2212 Strand

Bi-2212 offers a lot of opportunities for very high fields at low temperature. The current density is large under high fields, particularly with recent enhanced results. The Bi-2212 conductor may be a round strand: a very favorable shape to wind and to make high-current Rutherford cables required for protection. There is no satisfying high-current cable with YBCO. One drawback of Bi-2212 is their low mechanical properties. Large fields and current densities indeed induce high mechanical stresses. To improve the mechanical properties of Bi-2212 strands, Nexans has proposed to reinforce it with a metal sheath wrapped around using their process of shaping and welding. The sheath is wrapped around the strand and laser welded, and the whole is drawn to a diameter of 0.9 mm. Several materials for the sheath were studied to determine their resistance to thermal treatment of Bi-2212 and their mechanical properties after treatment. We choose Inconel 601. A method of perforating the sheath has been developed to enable the oxygenation during the heat treatment. A 6 + 1 conductor has also been produced around an Inconel core and inserted in a tube. The 6 + 1 reinforced conductor was then drawn to a diameter of 2.7 mm. The I c measurements at 4 K show that our mechanical reinforcement does not significantly lower the transport capacities. They therefore validate the method and the heat treatment.

Effects of Core Type, Placement, and Width on the Estimated Interstrand Coupling Properties of QXF-Type Nb&lt;sub&gt;3&lt;/sub&gt;Sn Rutherford Cables

The coupling magnetization of a Rutherford cable is inversely proportional to an effective interstrand contact resistance R eff , a function of the crossing-strand resistance R c , and the adjacent strand resistance Ra. In cored cables, R eff continuously varies with W, the core width expressed as percent interstrand cover. For a series of un-heat-treated stabrite-coated NbTi LHC-inner cables with stainless-steel (SS, insulating) cores, R eff (W) decreased smoothly as W decreased from 100%, whereas for a set of research-wound SS-cored Nb 3 Sn cables, R eff plummeted abruptly and remained low over most of the range. The difference is due to the controlling influence of R c - 2.5 μΩ for the stabrite/NbTi and 0.26 μΩ for Nb 3 Sn. The experimental behavior was replicated in the R eff (W )'s calculated by the program CUDI, which (using the basic parameters of the QXF cable) went on to show in terms of decreasing W that: 1) in QXF-type Nb 3 Sn cables (R c = 0.26 μΩ), Reff dropped even more suddenly when the SS core, instead of being centered, was offset to one edge of the cable; 2) R eff decreased more gradually in cables with higher R c 's; and 3) a suitable R eff for a Nb 3 Sn cable can be achieved by inserting a suitably resistive core rather than an insulating (SS) one.

Electro-mechanical properties of PIT Nb3Sn wires under transverse stress: experimental results and FEM analysis

Nowadays there is a great deal of interest in the scientific community in developing next-generation accelerator magnets based on high-Jc Nb3Sn Rutherford cables. Inside a cable the wires are subjected to the combined effect of axial and transverse load. Since Nb3Sn is a strain sensitive material, electromechanical characterization of cables is essential for magnet design. Testing a full-size Rutherford cable is an extremely complex and involved task. For this reason special Walters springs have been developed at the University of Geneva to test single wires under longitudinal and transverse load. In this work we analyze three PIT wires under transverse compressive load. To better understand the experimental results, a finite element model was developed. This model enabled better understanding of the mechanical behavior of the three samples and investigation of the mechanisms that determine wire performance degradation upon loading.