Superconducting magnets for accelerators were first suggested in the mid-60’s and have since become one of the major components of modern particle colliders. Technological progress has been slow but steady for the last half-century, based primarily on Nb–Ti superconductor. That technology has reached its peak with the Large Hadron Collider (LHC). Despite the superior electromagnetic properties of Nb3Sn and adoption by early magnet pioneers, it is just now coming into use in accelerators though it has not yet reliably achieved fields close to the theoretical limit. The discovery of the High Temperature Superconductors (HTS) in the late ’80’s created tremendous excitement, but these materials, with tantalizing performance at high fields and temperatures, have not yet been successfully developed into accelerator magnet configurations. Thanks to relatively recent developments in both Bi-2212 and REBCO, and a more focused international effort on magnet development, the situation has changed dramatically. Early optimism has been replaced with a reality that could create a new paradigm in superconducting magnet technology. Using selected examples of magnet technology from the previous century to define the context, this paper will describe the possible innovations using HTS materials as the basis for a new paradigm.

Quench detection capability is essential for reliable operation and protection of superconducting magnets, coils, cables, and machinery. We propose a quench detection technique based on sensing local temperature variations in the bulk of a superconducting winding by monitoring its transient acoustic response. Our approach is primarily aimed at coils and devices built with high-temperature superconductor materials where quench detection using standard voltage-based techniques may be inefficient due to the slow velocity of quench propagation. The acoustic sensing technique is non-invasive, fast, and capable of detecting temperature variations of less than 1 K in the interior of the superconductor cable stack in a 77 K cryogenic environment. We show results of finite element modeling and experiments conducted on a model superconductor stack demonstrating viability of the technique for practical quench detection, discuss sensitivity limits of the technique, and its various applications.

A robust fabrication technology is critical to achieve the high performance in YBa2Cu3O (YBCO) coils as the critical current of the brittle YBCO layer is subject to the strain-induced degradation during coil fabrication. The expected current-carrying capability of the magnet and its temperature dependence are two key inputs to the coil technology development. However, the expected magnet performance is not straightforward to determine because the short-sample critical current depends on both the amplitude and orientation of the applied magnetic field with respect to the broad surface of the tape-form conductor. In this paper, we present an approach to calculate the self-field performance limit for YBCO racetrack coils at 77 and 4.2 K. Critical current of short YBCO samples was measured as a function of the applied field perpendicular to the conductor surface from 0 to 15 T. This field direction limited the conductor critical current. Two double-layer racetrack coils, one with three turns and the other with 10 turns, were wound and tested at 77 and 4.2 K. The test coils reached at least 80% of the expected critical current. The ratio between the coil critical currents at 77 and 4.2 K agreed well with the calculation. We conclude that the presented approach can determine the performance limit in YBCO racetrack coils based on the short-sample critical current and provide a useful guideline for assessing the coil performance and fabrication technology. The correlation of the coil critical current between 77 K and 4.2 K was also observed, allowing the 77 K test to be a cost-effective tool for the development of coil technology.

A commercial Finite-Element-Analysis program, ANSYS®, is widely used in structural and thermal analysis. With the program's ability to include nonlinear material properties and import complex CAD files, one can generate coil geometries and simulate quench propagation in superconducting magnets. A "proof-of-principle" finite element model was developed assuming a resistivity that increases linearly from zero to its normal value at a temperature consistent with the assumed B magnetic field. More sophisticated models could easily include finer-grained coil, cable, structural, and circuit details. A quench is provoked by raising the temperature of an arbitrary superconducting element above its Tc. The time response to this perturbation is calculated using small time-steps to allow convergence between steps. Snapshots of the temperature and voltage distributions allow examination of longitudinal and turn-to-turn quench propagation, quench-front annihilation, and cryo-stability. Modeling details are discussed, and a computed voltage history was compared with measurements from a recent magnet test.

The design of a class of short period superconducting undulators is presented. We begin with a parameter-based analysis that provides insight into potential device performance as a function of the properties of superconducting materials. We present data on candidate low-temperature superconducting materials and the motivation to consider low-copper fraction, high Jc materials. Measured data on recent Nb3Sn conductors is provided, together with wire and cable design issues that are tailored for undulator applications. Key design concerns are then addressed, in particular the quench protection system limitations and the system performance. Progress on the construction and testing of a prototype 30mm period device is described.

An R&D effort is underway at Lawrence Berkeley National Laboratory (LBNL) to develop the technology of Nb 3Sn superconducting undulators (SCUs). Issues relating to the selection of the appropriate conductor are discussed. The design and fabrication of SCUs using Nb 3Sn 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 ∼70% of short-sample J c. Stability issues associated with flux-jumps and possible epoxy cracking are discussed. © 2005 IEEE.

The U.S. Fusion Energy Sciences Advisory Committee was charged “to identify the most promising transformative enabling capabilities (TEC) for the U.S. to pursue that could promote efficient advance toward fusion energy, building on burning plasma science and technology.” A subcommittee of U.S. technical experts was formed and received community input in the form of white papers and presentations on the charge questions. The subcommittee identified four “most promising transformative enabling capabilities”: 1. advanced algorithms 2. high critical temperature superconductors 3. advanced materials and manufacturing 4. novel technologies for tritium fuel cycle control. In addition, one second-tier TEC, defined as a “promising transformative enabling capability,” was identified: fast-flowing liquid-metal plasma-facing components. Each of these TECs presents a tremendous opportunity to accelerate fusion science and technology toward power production. Dedicated investment in these TECs for fusion systems is needed to capitalize on the rapid advances being made for a variety of nonfusion applications to fully realize their transformative potential for fusion energy.

Persistent magnetization currents are induced in superconducting filaments during the current ramping in magnets. The resulting perturbation to the design magnetic field leads to field quality degradation, particularly at low field, where the effect is stronger relative to the main field. The effects observed in NbTi accelerator magnets were reproduced well with the critical-state model. However, this approach becomes less accurate for the calculation of the persistent-current effects observed in Nb3Sn accelerator magnets. Here, a finite-element method based on the measured strand magnetization is validated using three state-of-the-art Nb3Sn accelerator magnets featuring different subelement diameters, conductor critical currents, magnet designs, and test temperatures. The temperature dependence of the persistent-current effects is reproduced. Based on the validated model, the impact of conductor design on the persistent-current effects is discussed. The strengths, limitations, and possible improvements of the approach are also discussed.

In response to the 2013 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) study was launched, as an international collaboration hosted by CERN. This study covers a highest-luminosity high-energy lepton collider (FCC-ee) and an energy-frontier hadron collider (FCC-hh), which could, successively, be installed in the same 100 km tunnel. The scientific capabilities of the integrated FCC programme would serve the worldwide community throughout the 21st century. The FCC study also investigates an LHC energy upgrade, using FCC-hh technology. This document constitutes the second volume of the FCC Conceptual Design Report, devoted to the electron-positron collider FCC-ee. After summarizing the physics discovery opportunities, it presents the accelerator design, performance reach, a staged operation scenario, the underlying technologies, civil engineering, technical infrastructure, and an implementation plan. FCC-ee can be built with today’s technology. Most of the FCC-ee infrastructure could be reused for FCC-hh. Combining concepts from past and present lepton colliders and adding a few novel elements, the FCC-ee design promises outstandingly high luminosity. This will make the FCC-ee a unique precision instrument to study the heaviest known particles (Z, W and H bosons and the top quark), offering great direct and indirect sensitivity to new physics.

In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100 km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre-of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries.