Clement Lorin

Accelerator-Quality HTS Dipole Magnet Demonstrator Designs for the EuCARD-2 5-T 40-mm Clear Aperture Magnet

Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The Enhanced European Coordination for Accelerator Research and Development (EuCARD-2) Work Package 10 is a collaborative push to take high-temperature superconductor (HTS) materials into an accelerator-quality demonstrator magnet. The demonstrator will produce 5 T stand alone and between 17 and 20 T when inserted into the 100-mm aperture of a Fresca-2 high-field outsert magnet. The HTS magnet will demonstrate the field strength and the field quality that can be achieved. An effective quench detection and protection system will have to be developed to operate with the HTS superconducting materials. This paper presents a ReBCO magnet design using a multistrand Roebel cable that develops a stand-alone field of 5 T in a 40-mm clear aperture and discusses the challenges associated with a good field quality using this type of material. A selection of magnet designs is presented as the result of the first phase of development.

The EuCARD-2 Future Magnets European Collaboration for Accelerator-Quality HTS Magnets

EuCARD-2 is a project supported by FP7-European Commission that includes, inter alia, a work-package (WP10) called “Future Magnets.” This project is part of the long term development that CERN is launching to explore magnet technology at 16 T to 20 T dipole operating field, within the scope of a study on Future Circular Colliders. The EuCARD2 collaboration is closely liaising with similar programs for high field accelerator magnets in the USA and Japan. The main focus of EuCARD2 WP10 is the development of a 10 kA-class superconducting, high current density cable suitable for accelerator magnets, The cable will be used to wind a stand-alone magnet 500 mm long and with an aperture of 40 mm. This magnet should yield 5 T, when stand-alone, and will enable to reach a 15 to 18 T dipole field by placing it in a large bore background dipole of 12-15 T. REBCO based Roebel cables is the baseline. Various magnet configurations with HTS tapes are under investigation and also use of Bi-2212 round wire based cables is considered. The paper presents the structure of the collaboration and describes the main choices made in the first year of the program, which has a breadth of five to six years of which four are covered by the FP7 frame.

The 16 T Dipole Development Program for FCC

A key challenge for a future circular collider (FCC) with centre-of-mass energy of 100 TeV and a circumference in the range of 100 km is the development of high-field superconducting accelerator magnets, capable of providing a 16 T dipolar field of accelerator quality in a 50 mm aperture. This paper summarizes the strategy and actions being undertaken in the framework of the FCC 16 T Magnet Technology Program and the Work Package 5 of the EuroCirCol.

Status of the Demonstrator Magnets for the EuCARD-2 Future Magnets Project

EuCARD-2 is a project partly supported by FP7 European Commission aiming at exploring accelerator magnet technology for 20-T dipole operating field. The EuCARD-2 collaboration is liaising with similar programs for high-field magnets in the U.S. and Japan. EuCARD-2 focuses, through the work package 10 “future magnets,” on the development of a 10-kA-class superconducting high-current-density cable suitable for accelerator magnets, for a 5-T stand-alone dipole of 40-mm bore and about 1-m length. After stand-alone testing, the magnet will be inserted in a large bore background dipole, 10-18 T. This paper reports on the design and development of models, which are called Feather0, wound with REBCO Roebel cable. Based on aligned block design to take advantage of the anisotropy of the REBCO tapes, Feather0 is a precursor of Feather2, which should reach the project goals in 2016. Feather0 is planned to be tested both in stand alone and as an insert mounted in the CERN Fresca facility providing 10-T background field. The progress of other designs pursued in the collaboration, one based on classical ϑ layout with Roebel cable and the other based on coil block with stacked tape cable, will be also reported.

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Next generation of dipole magnets with a field higher than 16 T are considered for future particle colliders. To do so, combined-technology magnets, made of Nb-Ti, Nb3Sn and high-temperature superconductor (HTS) materials, have to be developed to reduce the cost of such a magnet. Therefore, in the framework of the European Coordination for Accelerator Research and Development (EuCARD-2) project, many HTS dipole magnet designs have to be investigated to find the most effective design for the HTS insert in a graded magnet. This paper discusses the cos θ option. A 5-T stand-alone configuration of the HTS accelerator magnet (the first goal of EuCARD-2) appears to be achievable, whereas mechanical stress distribution shows that its use as an insert in a graded magnet is very challenging. This paves the way for alternative designs as the so-called slot or motor-like design, which is briefly introduced here.

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Distributed propulsion in aircraft brings many advantages in terms of efficiency and noise reduction. While the distribution can be done mechanically through the use of gears and transmissions, electrical propulsion allows for lower maintenance needs, higher efficiency, and lower emissions through the complete decoupling of the gas turbines and the propulsion fans. Such systems have been investigated in the past and NASA is executing on a development plan to bring turbo-electric propulsion systems for transportation aircraft by 2035. The very high specific power required for the airborne generators and motors can only be achieved by using superconductors. Analytical 2-D sizing models have been created and showed very promising results. NASA is now funding the development of higher fidelity models for superconducting machines in which an actual 3-D representation of the geometry is considered. The magnetic flux distribution is calculated using Biot-Savarts law coupled with the magnetic moment method for the backiron. The code also includes thermal and mechanical models allowing for a full and accurate design. The paper describes the model architecture and the methods used to perform high-temperature superconducting machine sizing and optimization.

Design of Dipole Inserts Made of REBCO-Roebel or BSCCO-Rutherford Cables

In the scope of the Future Circular Collider, work package 10, i.e., “Future Magnets,” of the EuCARD2 project aims at investigating accelerator quality magnets made of high-temperature superconductors. This paper deals with development of a cosϑ dipole relying on Roebel cable technology. In the first part, we present in detail the design of the dipole: the magnet generates 5 T in stand-alone mode with an overall current density of 684 A/mm2. When operating in a background field of 13 T, an extra field of 2 T can be provided by the cos ϑ insert due to mechanical limitations. A field increase up to 2.5 T is conceivable, providing the addition of inner shell reinforcement that would reduce the magnet aperture from 40 to 30 mm. In the second part, winding tests of dummy Roebel cable are reported. They demonstrate the challenges stemming from the relative slippage of the cable tapes while winding, which may be overcome by a lengthening of the longitudinal gap of the cable either by an increase of the transposition pitch or a decrease of the number of tapes in the cable. The cable shows a smooth winding behavior along the coil for two different magnet end designs and for its path outward the magnet.

Development of a 3D Sizing Model for All-Superconducting Machines for Turbo-Electric Aircraft Propulsion

Superconducting magnets can exhibit training quenches during successive powering to reaching nominal performance. The slip-stick motion of the conductors is considered to be one of the mechanisms of training. In this paper, we present a simple quantitative model where the training is described as a discrete dynamical system matching the equilibrium between the energy margin of the superconducting cable and the frictional energy released during the conductor motion. The model can be explicitly solved in the linearized case, showing that the short sample limit is reached via a power law. Training phenomena have a large random component. A large set of data of the large hadron collider magnet tests is postprocessed according to previously defined methods to extract an average training curve for dipoles and quadrupoles. These curves show the asymptotic power law predicted by the model. The curves are then fit through the model, which has two free parameters. The model shows good agreement over a large range, but it fails to describe the very initial part of the training.

Development of a Roebel-Cable-Based

EuCARD-2 is a project partly supported by FP7-European Commission aiming at exploring accelerator magnet technology for 20 T dipole operating field. The EuCARD-2 collaboration is liaising with similar programs for high field magnets in the USA and Japan. EuCARD-2 focuses, through the work-package 10 “Future magnets,” on the development of a 10 kA-class superconducting, high current density cable suitable for accelerator magnets, for a 5 T stand-alone dipole of 40 mm bore and about 1 m length. After standalone testing, the magnet will possibly be inserted in a large bore background dipole, to be tested at a peak field up to 18 T. This paper starts by reporting on a few of the highlight simulations that demonstrate the progress made in predicting: dynamic current distribution and influence on field quality, complex quench propagation between tapes, and minimum quench energy in the multitape cable. The multiphysics output importantly helps predicting quench signals and guides the development of the novel early detection systems. Knowing current position within individual tapes of each cable we present stress distribution throughout the coils. We report on the development of the mechanical component and assembly processes selected for Feather-M2 the 5 T EuCARD2 magnet. We describe the CERN variable temperature flowing helium cold gas test system. We describe the parallel integration of the FPGA early quench detection system, using pickup coils and temperature sensors, alongside the standard CERN magnet quench detection system using voltage taps. Finally we report on the first cold tests of the REBCO 10 kA class Roebel subscale coil named Feather-M0.

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AC losses need to be accurately estimated in order to develop more accurate thermal models for fully superconducting machines. In the framework of the development of a high-fidelity sizing tool for superconducting rotating machine for NASA, simulations showed that the classical models for ac losses, taking into account a purely alternating field, would not provide accurate estimations for the magnetization losses. Indeed, superconducting stators usually exhibit a large electrical loading and therefore are subjected to both alternating and rotating fields. As preliminary analysis, a numerical 2-D model is developed to calculate the magnetization losses generated by an elliptical magnetic field in a filament or round mono-core wire. The simulations are based on the H-formulation and executed using a commercial finite element analysis solver. The elliptical magnetic field applied to the superconducting wire is produced by a linear combination of both alternating and rotating fields. The load angle of the rotating machine, creating an angular shift between the alternating and rotating fields, has an impact on the losses and is taken into account. At this point of the study, no transport current is considered. We focus on the ratio between the effective losses and the losses created by a purely alternating field, which are considered known. The investigation leads to a fit formula of the ratio, which has been implemented in a high-fidelity superconducting machine model.