Magnet Development Program Research Articles

Impregnation damage monitoring for the canted-cosine-theta magnets using time-domain reflectometry

Impregnation plays a crucial role in the performance and protection of superconducting magnets. To investigate the impregnation status during quench training, a vector network analyzer (VNA)-based time domain reflectometry (TDR) is introduced. The proposed method and analyses focus on demonstrating their applicability within canted-cosine-theta (CCT) magnets, covering both artificially induced quenches using spot heaters and naturally occurring quenches. To verify the performance of the proposed method, VNA-based TDR is applied to CCT Subscale magnets developed in the US Magnet Development Program. The findings contribute to a deeper understanding of CCT superconducting magnet behavior and inform strategies for improving their performance.

Design and Assembly of a Large-Aperture Nb3Sn Cos-Theta Dipole Coil With Stress Management in Dipole Mirror Configuration

The stress-management cos-theta (SMCT) coil is a new concept which has been proposed and is being developed at Fermilab in the framework of US Magnet Development Program (US-MDP) for high-field and/or large-aperture accelerator magnets based on low-temperature and high-temperature superconductors. The SMCT structure is used to reduce large coil deformations under the Lorentz forces and, thus, the excessively large strains and stresses in the coil. A large-aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn SMCT dipole coil has been developed and fabricated at Fermilab to demonstrate and test the SMCT concept including coil design, fabrication technology and performance. The first SMCT coil has been assembled with 60-mm aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn coil inside a dipole mirror configuration and will be tested separately and in series with the insert coil. This paper summarizes the large-aperture SMCT coil design and parameters and reports the coil fabrication steps and its assembly in dipole mirror configuration.

Status of the High Field Cable Test Facility at Fermilab

Fermi National Accelerator Laboratory (FNAL) and Lawrence Berkeley National Laboratory (LBNL) are building a new High Field Vertical Magnet Test Facility (HFVMTF) for testing superconducting cables in high magnetic field. The background magnetic field of 15 T in the HFVMTF will be produced by a magnet provided by LBNL. The HFVMTF is jointly funded by the US DOE Offices of Science, High Energy Physics (HEP), and Fusion Energy Sciences (FES), and will serve as a superconducting cable test facility in high magnetic fields and a wide range of temperatures for HEP and FES communities. This facility will also be used to test high-field superconducting magnet models and demonstrators, including hybrid magnets, produced by the US Magnet Development Program (MDP). The paper describes the status of the facility, including construction, cryostat designs, top and lambda plates, and systems for powering, and quench protection and monitoring.

Electromechanical Analysis for the Integration of a Nb3Sn and a Bi-2212 CCT Dipole Magnet for a Hybrid Magnet Test

Within the U.S. Magnet Development Program, LBNL is planning to fabricate and test hybrid magnets combining Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and Bi-2212 canted-cosine theta (CCT) magnets. The first planned hybrid magnet test integrates a 1 m long, 90 mm bore Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole magnet (CCT5), and a 39 cm long, 30.8 mm bore Bi-2212 dipole magnet (BIN5c), which are already fabricated and were tested individually. The second planned hybrid magnet test integrates a 1.5 m long, 120 mm bore Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole magnet (CCT6), still under design, and a 1 m long, 40 mm bore Bi-2212 dipole magnet (BiCCT1), which is under fabrication. This work gives an update of the status of the Bi-2212 CCT magnet program, and focuses on the first hybrid magnet (CCT5/BIN5c). The electromagnetic and mechanical analysis of the CCT5/BIN5c hybrid magnet is presented, as well as the proposed mechanical assembly process. The quench protection strategy associated with the hybrid magnet test is also presented.

Development of a Bi2212 Dipole Insert at Fermilab

A goal of the U.S. Magnet Development Program (US-MDP) is high-field magnets for accelerators with magnetic fields larger than 15 T, i.e., above the limits of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn accelerator magnets. Composite round wires and Rutherford cables made of high temperature superconductor Bi2212 may achieve this goal. Bi2212 is sensitive to transverse stresses and strains, and this requires stress management in the coil design. A stress management approach was developed at Fermilab for high-field large-aperture Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn accelerator magnets. Now it is being applied to high-field dipole insert coils based on Bi2212 Rutherford cable. This paper describes the insert coil design and main parameters, including the superconducting wire and cable. The coil will be installed inside a 60-mm bore Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole outsert coil and cold iron yoke. The Bi2212 coil will be tested individually and in series with the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn outsert coil. The expected Bi2212 insert test parameters are reported and discussed.

Status of the Nb$_{3}$Sn Canted-Cosine-Theta Dipole Magnet Program at Lawrence Berkeley National Laboratory

As part of the US Magnet Development Program, Lawrence Berkeley National Laboratory (LBNL) is working on the development of high field stress-managed Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn dipole magnets using canted-cosine-theta (CCT) technology. As part of this program, a series of two layer magnets, CCT3/4/5, with short sample bore field of approximately 10 T and a 90 mm diameter open aperture have been designed, fabricated, and tested. The first magnet in the series, CCT3, was limited to less than 70% of the short sample current, this limitation is believed to be due to conductor damage. The second magnet in the series, CCT4, reached 86% of the short sample current, after changes to the groove geometry were made to accommodate dimensional changes in the cable during heat treatment. The third and final magnet of this series, CCT5, reached 88% of the short sample current with improved training relative to CCT4, after changes were made to the impregnation and assembly methods. While this two layer series was used to successfully demonstrate Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn CCT magnet technology, improvements in the training behavior of these magnets is desirable. For this purpose, a subscale program has been devised in order to probe the causes and explore reductions / improvements to training in stress-managed magnet technology. The subscale nature of the magnets allows for faster turnaround in the fabrication and testing process. In this paper, we present the design and test results for the first (baseline) subscale Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> Sn CCT magnet and demonstrate that the subscale platform and the larger two-layer magnets produce similar training results.

Development of a Small-Aperture Cos-Theta Dipole Insert Coil Based on Bi2212 Rutherford Cable and Stress Management Structure

The U.S. Magnet Development Program (US-MDP) is developing high-field accelerator magnets with magnetic fields beyond the limits of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn technology based on high temperature superconductor Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8-x</sub> (Bi2212). However, Bi2212 wires and cables are sensitive to transverse stresses and strains, which are substantial in high-field accelerator magnets. To prevent large degradation of the Bi2212 coils and achieve the required field quality, an innovative design which provides turn positioning during coil fabrication and operation and manage azimuthal and radial strains/stresses in the coil has been proposed at FNAL. This paper describes the development of a small-aperture two-layer Bi2212 dipole coil with stress management. The main parameters of the Bi2212 wire and Rutherford cable, the design of coil stress management structure and its plastic model, the coil mechanical analysis in the dipole mirror configuration are presented and discussed.

Design of CCT6: A Large Aperture, Nb$_3$Sn Dipole Magnet for HTS Insert Testing

We present the design of a four-layer, Canted Cosine Theta (CCT) Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_3$</tex-math></inline-formula> Sn dipole magnet as part of the general R&D program for high field superconducting magnets supported by the US Magnet Development Program (US-MDP). Future testing with High-Temperature Superconducting (HTS) inserts in a hybrid configuration motivates the design’s large clear aperture of 120 mm and target operating dipole field of 12 T at 4.2 K. First, we present a graded magnetic design utilizing existing Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_3$</tex-math></inline-formula> Sn cables which results in 30% operating current margin at the target field. We then share results from a 2D mechanical analysis which makes use of an idealized external structure to provide initial guidance for design studies. This mechanical analysis is extended to demonstrate compatibility of the CCT6 design with a mechanical support structure, based on key and bladder technology, currently considered for use within multiple US-MDP high-field magnet programs.

MDPCT1 Quench Data and Performance Analysis

MDPCT1is a four-layer cos-theta Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole demonstrator developed and tested at FNAL in the framework of the U.S. Magnet Development Program. The magnet reached record fields for accelerator magnets of 14.1 T at 4.5 K in the first test and 14.5 T at 1.9 K in the second test and then showed large degradation. While its inner coils performed exceptionally well with only two quenches up to 14.5 T and no evidence of degradation, the outer coils degraded over the course of testing. By adopting new measurement and analysis techniques at FNAL we are discussing in detail what happened. Both success and failure in our diagnostics are discussed. The evolution of techniques over the course of two tests (and three thermal cycles) shows the path to address challenges brought by the first four-layer magnet tested at FNAL. This paper presents the analysis of quench data along with diagnostic features and complementary measurements taken in support of the magnet performance analysis.

Design and Construction of a High Field Cable Test Facility at Fermilab

Fermi National Accelerator Laboratory, together with Lawrence Berkeley National Laboratory, is building a new High Field Vertical Magnet Test Facility (HFVMTF) to be situated in the Magnet Test Facility at Fermilab. The HFVMTF is jointly funded by the US DOE Offices of Science, High Energy Physics, and Fusion Energy Sciences, and will serve as a superconducting cable test facility for both communities. The background magnetic field for test samples is 15 T and will be produced by a magnet provided by LBNL operating at 1.9 K in superfluid helium. The samples will be placed in the background magnetic field, cooled to between 4.5 K and a user-specified upper limit, and will be powered with a superconducting transformer at up to 100 kA. Additionally, this facility will be used to test high-field superconducting magnet models and demonstrators, including hybrid magnets, produced by the US Magnet Development Program. Currently, the various tasks of the project are at different stages of execution, from conceptual to ready-for-construction designs. This paper describes the parameters and design status of the pit construction, cryostat, heat exchanger, lambda plate, power system, and quench protection and monitoring systems of the facility.

Reassembly and Test of High-Field Nb3Sn Dipole Demonstrator MDPCT1

In the framework of the U.S. Magnet Development Program (MDP), Fermilab has developed and tested a high-field Nb3Sn dipole demonstrator MDPCT1 for a post-LHC Hadron Collider. The magnet was first assembled with a lower coil pre-load to minimize the risk of coil damage during assembly and test. In the first test the magnet reached its test goal producing a world record field of 14.1 T at 4.5 K. Next the magnet was reassembled with nominal pre-load to achieve its design field limit of 15 T. This paper describes the details of MDPCT1 inspection, design modifications and reassembly. The magnet quench performance, including training, ramp rate and temperature dependences in the temperature range of 1.9-4.5 K, is presented and discussed.

Conceptual Design of a HTS Dipole Insert Based on Bi2212 Rutherford Cable

The U.S. Magnet Development Program (US-MDP) is aimed at developing high-field accelerator magnets with magnetic fields beyond the limits of Nb3Sn technology. Recent progress with composite wires and Rutherford cables based on the first generation high-temperature superconductor Bi2Sr2CaCu2O8−x (Bi2212) allows considering them for this purpose. However, Bi2212 wires and cables are sensitive to transverse stresses and strains, which are large in high-field accelerator magnets. This requires magnet designs with stress management concepts to control azimuthal and radial strains in the coil windings and prevent the degradation of the current carrying capability of Bi2212 conductor or even its permanent damage. This paper describes a novel stress management approach, which was developed at Fermilab for high-field large-aperture Nb3Sn accelerator magnets, and is now being applied to high-field dipole inserts based on Bi2212 Rutherford cables. The insert conceptual design and main parameters, including the superconducting wire and cable, as well as the coil stress management structure, key technological steps and approaches, test configurations and their target parameters, are presented and discussed.

Superconducting Accelerator Magnets Based on High-Temperature Superconducting Bi-2212 Round Wires

Superconducting magnets are an invaluable tool for scientific discovery, energy research, and medical diagnosis. To date, virtually all superconducting magnets have been made from two Nb-based low-temperature superconductors (Nb-Ti with a superconducting transition temperature Tc of 9.2 K and Nb3Sn with a Tc of 18.3 K). The 8.33 T Nb-Ti accelerator dipole magnets of the large hadron collider (LHC) at CERN enabled the discovery of the Higgs Boson and the ongoing search for physics beyond the standard model of high energy physics. The 12 T class Nb3Sn magnets are key to the International Thermonuclear Experimental Reactor (ITER) Tokamak and to the high-luminosity upgrade of the LHC that aims to increase the luminosity by a factor of 5–10. In this paper, we discuss opportunities with a high-temperature superconducting material Bi-2212 with a Tc of 80–92 K for building more powerful magnets for high energy circular colliders. The development of a superconducting accelerator magnet could not succeed without a parallel development of a high performance conductor. We will review triumphs of developing Bi-2212 round wires into a magnet grade conductor and technologies that enable them. Then, we will discuss the challenges associated with constructing a high-field accelerator magnet using Bi-2212 wires, especially those dipoles of 15–20 T class with a significant value for future physics colliders, potential technology paths forward, and progress made so far with subscale magnet development based on racetrack coils and a canted-cosine-theta magnet design that uniquely addresses the mechanical weaknesses of Bi-2212 cables. Additionally, a roadmap being implemented by the US Magnet Development Program for demonstrating high-field Bi-2212 accelerator dipole technologies is presented.

Structural Diagnostics of Superconducting Magnets Using Diffuse Field Ultrasound

Among various diagnostics, acoustic techniques are valuable for characterizing mechanical instabilities associated with lengthy training, premature quenching and other performance limitations of high-field accelerator magnets. While acoustic emissions from magnets were studied since early 80 s, techniques involving external acoustic excitation have so far been of limited use. As such techniques are already well-developed in materials science and geoscience, they offer a great potential for the superconducting magnet applications. In a typical magnet coil an acoustic pulse emitted by a coupled ultrasonic transducer would experience multiple scatterings from boundaries and interfaces along its propagation path, in resemblance to a diffusion process. The resulting diffuse ultrasonic field uniquely samples geometrical boundaries, scatterer locations and sound velocity distribution in the propagation medium. Variation of these properties can be tracked in real time and with high accuracy by monitoring shape distortions and temporal shift of the ultrasonic waveforms acquired by sensors coupled to the coil. We discuss key physical principles and capabilities of diffuse field ultrasound, and give examples of using it for detecting interface instabilities in Canted Cosine Theta (CCT) Nb3Sn superconducting accelerator magnets built by the US Magnet Development Program.

First Field Measurements of the 15 T Nb3Sn Dipole Demonstrator MDPCT1

Within the US Magnet Development Program (MDP), a 15 T Nb3Sn dipole was developed to demonstrate a possible magnet design for a post-LHC proton-proton Collider. The magnet design is based on 60 mm aperture 4-layer shell-type coils, graded between the inner and outer layers to maximize magnet performance. Magnet coils are surrounded by vertically split thick iron laminations, connected by aluminum I-clamps, and a thick stainless-steel skin. The magnet coils were preloaded to achieve 14 T in the first test. The magnet was tested at the Vertical Magnet Test Facility (VMTF) at Fermilab. This paper reports the first results of magnetic measurements of the 15 T Nb3Sn dipole demonstrator, including dipole strength, geometrical harmonics, coil magnetization and iron saturation effects. At the maximum quench current of 9742 A we obtained a dipole strength of 14.13 T.

Development and First Test of the 15 T Nb3Sn Dipole Demonstrator MDPCT1

Fermilab in the framework of the U.S. Magnet Devel-opment Program (MDP) has developed a $Nb_3Sn$ dipole demonstrator for a post-LHC hadron collider. The magnet uses 60-mm aperture 4-layer shell-type graded coils. The cable in the two inner-most layers has 28 strands 1.0 mm in diameter and the cable in the two outermost layers has 40 strands 0.7 mm in diameter. An inno-vative mechanical structure based on aluminum I-clamps and a thick stainless steel skin is used to preload $Nb_3Sn$ coils and support large Lorentz forces. The maximum field for this magnet is limited by 15 T due to mechanical considerations. The first magnet assembly was done with lower coil pre-load to achieve 14 T and minimize the risk of coil damage during assembly. This paper describes the magnet design and the details of its assembly procedure, and re-ports the results of its cold tests.

Assembly and Tests of Mechanical Models of the 15-T Nb3Sn Dipole Demonstrator

Within the U.S. magnet development program, Fermilab is developing a 15-T Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole demonstrator. Prior to the construction of the real magnet model, short sections and the whole structure were instrumented with strain gauges and assembled to validate the results of structural analysis, check tooling, and to gain experience with the assembly of the real magnet components. This paper summarizes the lessons learned from these mechanical models and compares the measured data with the finite-element analysis.

Fabrication of Bi-2212 Canted-Cosine-Theta Dipole Prototypes

Author(s): Fajardo, LG; Brouwer, L; Caspi, S; Hafalia, A; Hernikl, C; Prestemon, S; Shen, T; Bosque, E; English, C | Abstract: The U.S. Magnet Development Program (MDP) is exploring the possibility of combining low-and higherature superconductor technologies, using cosine-theta and canted-cosine-theta (CCT) Nb3Sn dipole magnets together with Bi-2212 CCT inserts, with the ultimate goal of constructing a 20-T dipole. The MDP short-term goal is a Bi-2212 CCT insert capable of reaching 5 T in the bore when operating as a stand-alone and 3 T when operating under a background field of 15 T. This paper reports on the fabrication of our BIN4 dipole magnet and our BIN5a and BIN5b coils, designed and built at the Lawrence Berkeley National Laboratory to address potential fabrication issues of Bi-2212 coils and verify the design of our 18-20-T dipole magnet. BIN4 is a two-layer 50-cm-long CCT magnet that uses a nine-strand Rutherford cable made with 0.8-mm-diameter Bi-2212 strands. Its goal is to investigate critical current, insulation integrity, manufacturing challenges, and quench protection issues after heat treating both layers together under oxygen at standard atmosphere (1 bar). BIN5a and BIN5b are two identical coils, similar to the outer layer of BIN4, with the difference that the length is 39 cm, and they will undergo 50-bar overpressure processing heat treatment. BIN5 coils are made from the state-of-the-art strand with an engineering critical current density of 1150 A/mm2 at 4.2 K and 5 T.

Mechanical Utility Structure for Testing High Field Superconducting Dipole Magnets

The U.S. Magnet Development Program (MDP) collaboration is designing a utility mechanical structure for testing various high-field superconducting dipole coils. The design uses a shell-based structure concept, which allows applying preload in two steps: during a room temperature assembly and during a cool down to a cryogenic temperature. The structure is designed to accommodate various coil designs-including Nb3Sn Cosine Theta (CT) and Canted CT magnets as well as hybrid magnets with high temperature superconductor cables. Superconducting coils, enclosed by bolted pads to form an octagonal coil pack, will be inserted into a reusable yoke-shell subassembly and precisely preloaded during the assembly using a bladder-and-key technology. Due to a differential thermal contraction between an external aluminum shell and the magnet core, the coil preload increases during the cool down up to level required for 17-T excitation. Such a reusable structure will serve as a testing fixture supporting goals of the MDP program, decreasing cost and simplifying coil performance testing at different preload levels. We present a finite-element analysis of the structure preloading various coil designs and examine the predicted coil stress at each step of the magnet assembly and excitation.

FEA Model and Mechanical Analysis of the Nb3Sn 15-T Dipole Demonstrator

Nb3Sn magnets with a nominal operation field of ∼15 T are being considered for the large hadron collider (LHC) energy upgrade high-energy large hadron collider (HE-LHC) and a post-LHC future circular collider. To demonstrate the feasibility of 15-T accelerator quality dipole magnets, the U.S. magnet development program is developing a single-aperture 15-T Nb3Sn dipole demonstrator based on a 4-layer graded cos-theta coil with 60 mm aperture and cold iron yoke. The main design challenges for 15-T accelerator magnets include large Lorentz forces at this field level. To counteract them, an innovative mechanical structure based on a vertically split iron yoke, locked by large aluminum IC-clamps and supported by a thick stainless steel skin, has been developed at Fermilab. To study the performance of the structure, a parametric multiphysics finite element analysis (FEA) model has been set up. This paper describes the numerical model as well as the results of a sensitivity analysis of the effect of geometrical tolerances and assembly parameters.