Showing papers in "IEEE Transactions on Applied Superconductivity in 2023"

Status of the MQXFB Nb3Sn Quadrupoles for the HL-LHC

Abstract: The cold powering test of the first two prototypes of the MQXFB quadrupoles (MQXFBP1, now disassembled, and MQXFBP2), the Nb3Sn inner triplet magnets to be installed in the HL-LHC, has validated many features of the design, such as field quality and quench protection, but has found performance limitations. In fact, both magnets showed a similar phenomenology, characterized by reproducible quenches in the straight part inner layer pole turn, with absence of training and limiting the performance at 93% (MQXFBP1) and 98% (MQXFBP2) of the nominal current at 1.9 K, required for HL-LHC operation at 7 TeV. Microstructural inspections of the quenching section of the limiting coil in MQXFBP1 have identified fractured Nb3Sn sub-elements in strands located at one specific position of the inner layer pole turn, allowing to determine the precise origin of the performance limitation. In this paper we outline the strategy that has been defined to address the possible sources of performance limitation, namely coil manufacturing, magnet assembly and integration in the cold mass.

Onset of Mechanical Degradation due to Transverse Compressive Stress in Nb3Sn Rutherford-Type Cables

Abstract: In the framework of the High Field Magnets program at CERN, lower limits of degradative mechanical loads on reacted and impregnated Nb3Sn Rutherford-type cables are being studied with the goal of optimizing the pre-stress applied at room temperature on the accelerator magnets. Coils are loaded during assembly, for instance when transverse load is applied by using a collaring press or the bladder and key technique. Nb3Sn is susceptible to transverse compressive stress, which is the loading condition investigated for this study. The purpose of this work is to identify the maximum pressure that can be applied, at room temperature, to reacted cables without generating cracks in the Nb3Sn subelements and to quantify the crack propagation with increasing pressure. Metallographic techniques are used to examine the onset and evolution of damage in the transverse planes of impregnated double-stacked Rutherford-type cable specimens with increasing stress. The damage pattern observed at subelement, strand and cable levels is described. Two reaction heat treatment cycles are analyzed.

The Challenges and Solutions of Meeting the Assembly Specifications for the 4.5 m Long MQXFA Magnets for the Hi-Luminosity LHC

Abstract: The U.S. High-Luminosity LHC Accelerator Upgrade Project (HL-LHC AUP) has, in the recent years, developed assembly specifications for the 4.5 m long MQXFA magnets, which are 150 mm aperture high-field Nb3Sn low-β quadrupole magnets that are being built for the CERN Hi-Luminosity LHC (HL-LHC) upgrade. While the specifications were based on lessons learned from the LHC Accelerator Research Program (LARP) effort and the MQXFS and MQXFA prototype magnets, the experience gained from having both MQXFA07 and MQXFA08 magnets not meeting performance specifications during cold testing actually catalyzed a better understanding of the impact of the target assembly specifications and a subsequent refinement of the same. This paper summarizes a body of assembly data from the Pre-Series (MQXFA03-MQXFA07) and Series magnets (MQXFA08-MQXFA11) that have been built to date, and discusses the processes employed to successfully face the challenge of ensuring that the assembly specifications are met for the duration of the project.

Role of Insulation Materials and Cryogenic Coolants on Fault Performance of MW-Scale Fault-Tolerant Current-Limiting Superconducting Transformers

Abstract: Fault-tolerant current-limiting (FTCL) high-temperature superconducting (HTS) transformers are promising components for playing a role in renewable energy integrated modern power systems. In this article, the impact of different insulation materials and cryogenic coolant fluids on the electro-thermal characteristic of an MW-scale FTCL-HTS transformer is investigated. For this purpose, an equivalent circuit model (ECM) is established to characterize the temperature, recovery time, and fault tolerability of FTCL-HTS transformer under different conditions. The proposed ECM is firstly validated using experimental results of a typical HTS transformer. After that the model is developed for a 50 MVA, 132 kV/13.8 kV HTS transformer. In order to add fault tolerance capability to the 50 MVA HTS transformer, three strategies were considered in this article. In the first strategy, the effect of three insulation materials (including Kapton tapes, Nomex papers, and Acrylated Urethane solid insulation) covering HTS tapes was investigated on fault performance. The second strategy was changing cryogenic fluid to liquid hydrogen instead of liquid nitrogen. As for the last strategy, the impacts of thickness and material properties of stabilizer in HTS tape were investigated on the maximum temperature and recovery time of HTS transformer. Results show that by using these strategies, the maximum temperature of HTS tape of transformer winding under a short circuit fault was reduced.

64-GHz Operation of the Pseudorandom Binary Sequence Generator Using the Dual RSFQ/ERSFQ Standard Cell Library

Abstract: A pseudorandom binary sequence of 7-bit word length (PRBS-7) generator has been designed as a low complexity circuit to validate the dual RSFQ/ERSFQ standard cell library, the circuit simulation methodology using process corners and Monte-Carlo statistical variations, as well as the digital design methodology using Verilog simulations with load-dependent timing back-annotation. The PRBS-7 design was optimized across multiple process corners with Monte-Carlo circuit simulations by incorporating statistical variations of the process parameters. To validate the digital design flow, the PRBS-7 was simulated using the Verilog behavioral descriptions of library cells. Using Liberty files for different global bias current (XI) process corners, the margins obtained from digital simulation were compared with circuit simulations. A 5 mm × 5 mm chip, incorporating both the RSFQ and ERSFQ variant of the PRBS-7, was fabricated in the MIT-LL 100 μA/μm2 SFQ5ee fab node. The RSFQ variant of the PRBS-7 has been successfully tested up to 64.77-GHz clock frequency, and the ERSFQ variant up to 45.72-GHz clock frequency. In addition, we have analyzed the model-to-hardware correlation for RSFQ PRBS-7 for different clock frequencies. The simulations account for two process parameters, critical current density (Jc), and sheet resistance (Rs).

Progress Toward Superconductor Electronics Fabrication Process With Planarized NbN and NbN/Nb Layers

Abstract: In order to increase circuit density of superconductor digital and neuromorphic circuits by 10× and reach integration scale of 108 Josephson junctions (JJs) per chip, we developed a new fabrication process on 200-mm wafers, using self-shunted Nb/Al-AlOx/Nb JJs and kinetic inductors for cell miniaturization. The process has one layer of JJs, one layer of resistors, and ten fully planarized superconducting layers: 8 niobium layers and two layers of high kinetic inductance materials, Mo2N and NbN, with sheet inductance of 8 pH/sq and 3 pH/sq, respectively. The minimum linewidth of NbN kinetic inductors is 250 nm. NbN films were deposited by two methods: with ${T}_c \approx $15.5 K by reactive sputtering of a Nb target in Ar+N2 mixture; with ${T}_c$ in the range from 9 K to 13 K by plasma-enhanced chemical vapor deposition (PECVD) using Tris(diethylamido)(tert-butylimido)niobium(V) metalorganic precursor. PECVD of NbN was investigated to obtain conformal deposition and filling narrow trenches and vias with high depth-to-width ratios, d/w>1, which was not possible to achieve using sputtering and other physical vapor deposition methods at temperatures below 200 °C required to prevent degradation of Nb/Al-AlOx/Nb junctions. Nb layers with 200 nm thickness are used in the process layer stack as ground planes to maintain a high level of interlayer shielding and low intralayer mutual coupling, for passive transmission lines with wave impedances matching impedances of JJs, typically ≤50 Ω, and for low-value inductors. NbN and NbN/Nb bilayer are used for cell inductors. Using NbN/Nb bilayers and individual pattering of both layers to form inductors allowed us to increase critical currents of the interlayer vias and minimize parasitic kinetic inductance associated with the vias and connections to JJs. Fabrication details and results of electrical characterization of NbN films, wires, and vias, and comparison with Nb properties are given.

Analysis of the Magnetization-Induced Field Error in a Superconducting Bending Magnet for a Compact, Rapid-Cycling Heavy-Ion Synchrotron

Abstract: An ongoing design study of a 90-degree superconducting bending magnet (SCBM) is being conducted for a compact, rapid-cycling heavy-ion synchrotron at the National Institutes for Quantum Science and Technology (QST). The SCBM is designed to generate a 3.5 T dipole field and a 1.5 T $\cdot$ m$^{-1}$ quadrupole field for bending and horizontally defocusing heavy-ion beams. Since a heavy-ion beam is injected into the synchrotron at the field of 0.3 T, and accelerated to 3.5 T in 5 s, and then it is extracted at the field range from 1.1 T to 3.5 T, field errors derived from the magnetization at such a ramp rate will cause instability of the beam during the acceleration. In this paper, the field errors derived from both the DC and the AC effects are analyzed with numerical models in two dimensions (2D). The DC effects from the screening current in the superconducting coil and iron hysteresis behavior are estimated by the nested ellipse model and the finite element method (FEM) coupled with an inverse Jiles-Atherton model. The AC effects from the eddy current generated in the thermal shield, the beam pipe and the thermal path are estimated by a transient FEM analysis and analytical method. The change of the field error due to the magnetization is estimated to be about 1 unit at the time of beam injection.

Design Evolution of MADMAX Conductor to a Nb–Ti Cable in Copper Conduit

Abstract: The MAgnetized Disc and Mirror Axion eXperiment (MADMAX) project aims at detecting axion dark matter in the mass range around 100 μeV. Prerequisite for success is a very large dipole (1.35-m warm bore) with a high magnetic field up to 10 T. A first conductor design made of Nb–Ti Rutherford cable on conduit conductor with a hole in the copper conduit (RCOCC type) was already presented. The coolant is static bath of superfluid helium at 1.8 K. Unfortunately, no conductor manufacturer with an available production line was found to take in charge the cable insertion/soldering process. Actually, such a production line should be compatible with large conductor section (∼400 mm2), including a solder wave device. The type of conductor was changed to use a line developed for ITER cable-in-conduit conductor. Nevertheless, the jacket part was kept in copper. The main evolution of the MADMAX conductor design is presently reviewed. The final outer dimensions of the conductor, the void fraction, and the required cold work of the copper induce a reverse engineering challenge on the initial shape of the copper profile. Then, the cable geometry modification involves a lots of differences in terms of self-field, strand diameters, transposition paths, joints technique, and conductance between the strands and the stabilizer. The mechanical aspects are subject to evolution for the project due to the magnetic design optimization and conductor-type change. A submodeling approach is used to detail the stress level in the stabilizer jacket. The possibility of wire motion and wire deformation during the conductor compaction in the production line is also discussed. Concerning the thermal analysis, the major difference is the thermohydraulic quench back that induces a much higher pressure drop of the helium in the conduit. So, higher pressure-induced higher helium velocity and a fast detection after a quench event in superfluid environment become possible.

Straight and Curved Canted Cosine Theta Superconducting Dipoles for Ion Therapy: Comparison Between Various Design Options and Technologies for Ramping Operation

Abstract: Canted Cosine Theta layout for accelerator magnets is a very attractive since such magnets can be manufactured and assembled without big tooling, and with a relatively modest number of parts and tools. In the frame of European Horizon2020 funds, two collaborations, HITRIplus and I.FAST, are developing a CCT design, of 80 mm free bore, 4 T central dipole field, and 0.4 T/s ramp-rate. This magnet is expected to be the bending element of a gantry, to control the beam delivery in therapy with ions (hadrontherapy). The paper illustrates first a comparison between CCT and more classical cosine theta layout, followed by the comparison between Nb-Ti, Nb3Sn, MgB2, and HTS tapes coils. Relevant requirement for the magnets of this study is to be operated at low current, to limit the heat generation, in sight of a liquid-free cooling system. The results of the comparison is then applied to the design of two magnet demonstrators. Both adopt a low-losses Nb-Ti rope, consistently with the need for keeping the heat generation as low as possible. The first is a straight combined function dipole-quadrupole, while the second is a curved CCT dipole. The paper concludes with the first manufacturing tests for the CCT formers, for which aluminium -bronze, stainless steel and charged PEEK polymer are being explored as basic material.

Large-Area Niobium Titanium Nitride Superconducting Microstrip Single-Photon Detector Fabricated Using a Photolithography Process

Abstract: In this paper, we present a large-area niobium titanium nitride (NbTiN) superconducting microstrip single-photon detector (SMSPD) fabricated using a photolithography process. We fabricated a 1-μm-wide NbTiN-SMSPD covering 420 × 420 μm2 active area with a filling factor of 20% using an i-line stepper. The detector is cooled down to approximately 2.2 K, and its performance is evaluated at the wavelengths from visible to near-infrared. The detector operates stably without a shunt resistor and shows single-photon sensitivity for photons with a wavelength of 1550 nm. The bias current dependence of the detection count rate is measured at the wavelengths from 406 to 1550 nm. The saturation of the detection count rate with increasing the bias current was successfully observed at wavelengths below 850 nm, suggesting an internal detection efficiency approaching 100%. Furthermore, we evaluated the timing jitter performance using the femtosecond pulse laser with a wavelength of 1550 nm. Consequently, we achieved a system timing jitter of 85 ps for a light spot diameter of 100 μm.

60-GHz Single Flux Quantum Pulse Transfer Circuit for Serial Biasing

Abstract: Serial Biasing (SB) is a technique to reduce the total DC bias current of Rapid Single Flux Quantum (RSFQ) circuits by partitioning a design into several islands with isolated grounds and sequential biasing. In this paper we focus on the design of a driver-receiver pair (DRP) to transfer pulses between islands that are galvanically isolated for pulse streams. We discuss both DRP itself and the structure for its testing, that comprises several DRPs connected in series, on-chip pseudo random binary sequence (PRBS) generator for circuit stimulation, and HF output interface. We use the layout of DRPs’ chain as an example to illustrate the advantage of the grapevine (GV) approach, introduced earlier, to manage the bias current flowing into and out of an island. The GV current management technique is analyzed by both electromagnetic simulations and measurement, compared, and contrasted with the so-called ‘straightforward’ (SF) approach. The maximum operational frequency for SF test structure was 10 GHz with zero margins for the SB current. Measurements of the GV structure at 10 GHz demonstrated BER of 10−12 with ±5.8% margins for SB current. We observed the correct operation of the 5-island DRP chain up to 60 GHz using the grapevine approach for SB current management. All chips were fabricated at MIT Lincoln Laboratory using SFQ5ee fab node.

Applied Metrology for the Assembly of the Nb3Sn MQXFA Quadrupole Magnets for the HL-LHC AUP

Abstract: The US HL-LHC Accelerator Upgrade Project (AUP) is building Nb3Sn quadrupole magnets, called MQXFA, with plans to install 16 of them in the HL-LHC Interaction Regions. Variability in coil size must be dealt with at the assembly level, which requires timely and repeatable measurement of each coil. In this paper we will present the methodology used for coil measurements and the geometrical size data for the coils that have been measured thus far. We will also show the coil measurements of 8 coils before and after cold test. The Leica AT960-MR laser tracker with Spatial Analyzer software acquired to achieve these measurements has been used elsewhere in the project to great effect.

A Novel Design for Improving the Control on the Stainless-Steel Vessel Welding Process for Superconducting Magnets

Abstract: Stainless steel vessels see widespread use in superconducting magnets for particle accelerator applications. Their function varies in different magnet designs: they always provide the necessary liquid helium containment, but in some cases are also used to provide azimuthal prestress and can also be welded to the magnet end plate to provide additional longitudinal stiffness. A magnet designed with the bladder and key technology does not rely on the structural role of the vessel. They are structurally supported using azimuthally prestressed aluminum shells, and the longitudinal constraint by rods. In this case, the magnet designer would generally like to minimize the interaction between the magnet and the stainless-steel vessel and to minimize the coil stress variation due to the vessel. The stress state in the vessel and in the coil is a function of the circumferential interference, defined as the vessel azimuthal length minus the magnet circumference. The vessel and the magnet azimuthal length machining tolerances are relatively large resulting in significant stress variations in the superconducting coils. In this paper we introduce an interference-control shim, which can significantly limit the stress variation of the coils for a given variation of the interference. The effectiveness of the interference-control shim is evaluated numerically on the MQXF, the low-$\beta$ quadrupole for the High Luminosity LHC.

Basic Coil Structure for Rapid Charge in a Low-Frequency and High-Efficiency Wireless Power Transmission System Using High-Temperature Superconducting Coil for Railway Vehicle

Abstract: We have been investigating the possibility of a low-frequency and high-efficiency wireless power transmission (WPT) system for the railway vehicle using a high-temperature superconducting (HTS) coil. We investigated a basic HTS coil structure having a low ac loss and a high coupling coefficient between the primary and secondary coils by adjusting a radial gap between turns. The devised HTS coil was configured to have a radial gap approximately equal to the HTS tape width and increase the number of turns while reducing the inner diameter of the coil. Also, we analyzed the power transmission characteristics in the 40 kW class WPT system using the devised HTS coils operated at a low frequency around 1 kHz for the railway vehicle. Furthermore, we fabricated the 1 kW class WPT model system at an operating frequency of 0.92 kHz using the devised HTS coil and demonstrated the effectiveness of the low-frequency and high-efficiency WPT system using the devised HTS coil structure. As a result, we clarified that the low-frequency WPT system using the devised HTS coil for the railway vehicle can perform more rapid charging and the high-efficiency transmission than that using the copper coils.

Design of a Helium-Free Test Cryostat for Superconducting Wires, Cables, and Windings

Abstract: A helium-free test cryostat is being built to support testing of superconducting wires, cables, and windings. Three cryocoolers are mounted on the top hat of an LN2-shielded open-top cryostat and used to heat-sink thermal intercept shells at 50 K, 20 K, and 4.2 K. Ternary leads are used for supply and return of a 10 kA circuit (for a background-field dipole) and a 20 kA circuit for a test sample. Each lead is a series connection of a N2 vapor-cooled lead and a Bi-2223 Type G lead. A closed-flow liquid helium loop is used to maintain the Nb3Sn CIC windings of a 10 T background field dipole at 5 K. The objective of the design is to make it possible to sustain the test environment relying solely on LN2 and three cryocoolers, without the expense of a helium liquefier or a large inventory of liquid helium.

Conceptual Design of a 20 T Hybrid Cos-Theta Dipole Superconducting Magnet for Future High-Energy Particle Accelerators

Abstract: High energy physics research will need more and more powerful circular accelerators in the next decades. It is therefore desirable to have dipole magnets able to produce the largest possible magnetic field, in order to keep the machine diameter within a reasonable size. A 20 T dipole is considered a desired achievement since it would allow the construction of an 80 km machine, able to circulate 100 TeV proton beams. In order to reach 20 T, a hybrid Low-Temperature Superconductor (LTS) - High-Temperature Superconductor (HTS) magnet is needed, since LTS technology is presently limited to ∼16 T for accelerator magnet applications. In this paper, we present the design of a 6 layers 20 T hybrid dipole magnet using Nb3Sn (LTS) and Bi2212 (HTS). We show that it is possible to achieve this magnetic field with accelerator field quality, with sufficient margin on a realistic conductor, keeping the stresses within safe limit, avoiding conductor degradation.

Numerical Assessment of the Inhomogeneous Temperature Field and the Quality of Heat Extraction of Nb3Sn Impregnated Magnets for the High Luminosity Upgrade of the LHC

Abstract: The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN foresees the installation of Nb3Sn-based quadrupole magnets at selected interaction points of the accelerator. The precise knowledge of each magnet's thermal characteristics and heat extraction performance in response to power depositions during both nominal and ultimate conditions is essential in determining safe operating margins. A 2D numerical framework has been developed to systematically assess the temperature distribution in the combined magnet structure-superfluid He system of each magnet and enveloping cold mass using open-source software. Here a full cross-section of a magnet cold mass is modelled, under the power density distribution expected at the most exposed longitudinal position during accelerator operation at an instantaneous luminosity of 5.0 × 1034 cm−2s−1, corresponding to the nominal conditions for HL-LHC. Temperature maps and margins are presented for the inner triplet magnets (MQXF) for both horizontal and vertical beam crossing conditions, along with the validation of the design of cold mass cooling channels for heat extraction.

Conceptual Design of 20 T Hybrid Accelerator Dipole Magnets

Abstract: Hybrid magnets are currently under consideration as an economically viable option towards 20 T dipole magnets for next generation of particle accelerators. In these magnets, High Temperature Superconducting (HTS) materials are used in the high field part of the coil with so-called “insert coils”, and Low Temperature Superconductors (LTS) like Nb3Sn and Nb-Ti superconductors are used in the lower field region with so-called “outsert coils”. The attractiveness of the hybrid option lays on the fact that, on the one hand, the 20 T field level is beyond the Nb3Sn practical limits of 15-16 T for accelerator magnets and can be achieved only via HTS materials; on the other hand, the high cost of HTS superconductors compared to LTS superconductors makes it advantageous exploring a hybrid approach, where the HTS portion of the coil is minimized. We present in this paper an overview of different design options aimed at generating 20 T field in a 50 mm clear aperture. The coil layouts investigated include the Cos-theta design (CT), with its variations to reduce the conductor peak stress, namely the Canted Cos-theta design (CCT) and the Stress Management Cos-theta design (SMCT), and, in addition, the Block-type design (BL) including a form of stress management and the Common-Coil design (CC). Results from a magnetic and mechanical analysis are discussed, with particular focus on the comparison between the different options regarding quantity of superconducting material, field quality, conductor peak stress, and quench protection.

Continuous Fiber Bragg Grating Optical Sensors for Superconducting Magnet Quench Detection: The Effects of Attenuation and Position in the Array

Abstract: Quasi-continuous arrays of fiber Bragg gratings (FBGs) show great promise for quench protection in superconductors. The number of identical gratings and the reflectivity of the individual gratings are important parameters determining the sensitivity of the system to a local temperature or strain perturbation. We apply strain to shift the Bragg wavelength of a single FBG through the spectrum of an array of up to 1000 identical gratings, and map out the detection sensitivity for a given $\Delta \lambda$ relative to the peak reflectance of the FBG array, and show that the position of the perturbed FBG matters only due to the broadband attenuation of the probe light down the array. Varying the number of gratings in the array shows the interplay between the number of gratings, the reflectivity of the gratings, and the sensitivity of the system. We demonstrate that the ability to model the spectrum of the FBG array is crucial to predicting system performance.

Correcting Gain Drift in TES Detectors for Future X-Ray Satellite Missions

Abstract: Changes in the operating environment of transition-edge sensor (TES) microcalorimeters can cause variations in the detector gain function over time. If not corrected, this can degrade the spectral resolution, and cause systematic errors in the knowledge of the absolute energy. The non-linear nature of the TES energy scale function and the potential for multiple, simultaneous sources of drift can make effective corrections extremely challenging. Satellite instruments typically employ an on-board calibration source to provide known reference X-ray lines. This allows real-time monitoring of the detector gain stability and provides information that can be used to correct for drifts. Here we discuss progress towards demonstrating that the energy scale requirements can be met for future instruments such as Athena X-IFU. We present measurements (from ∼1–12 keV) on ∼200 pixels in a prototype X-IFU array. We use a non-linear drift correction algorithm that uses two fiducial calibration lines (5.4 keV and 8.0 keV) to track gain and interpolate a new, corrected gain between a set of three pre-calibrated gain functions that span the anticipated range of induced drifts. We demonstrate this algorithm is effective at correcting the full gain scale in the presence of multiple sources of environmental drift.

Challenges and Lessons Learned From Fabrication, Testing, and Analysis of Eight MQXFA Low Beta Quadrupole Magnets for HL-LHC

Abstract: By the end of October 2022, the US HL-LHC Accelerator Upgrade Project (AUP) had completed fabrication of ten MQXFA magnets and tested eight of them. The MQXFA magnets are the low-beta quadrupole magnets to be used in the Q1 and Q3 Inner Triplet elements of the High Luminosity LHC. This AUP effort is shared by BNL, Fermilab, and LBNL, with strand verification tests at NHMFL. An important step of the AUP QA plan is the testing of MQXFA magnets in a vertical cryostat at BNL. The acceptance criteria that could be tested at BNL were all met by the first four production magnets (MQXFA03-MQXFA06). Subsequently, two magnets (MQXFA07 and MQXFA08) did not meet some of the criteria and were disassembled. Lessons learned during the disassembly of MQXFA07 caused a revision to the assembly specifications that were used for MQXFA10 and subsequent magnets. In this article, we present a summary of: 1) the fabrication and test data for all the MQXFA magnets; 2) the analysis of MQXFA07/A08 test results with characterization of the limiting mechanism; 3) the outcome of the investigation, including the lessons learned during MQXFA07 disassembly; and 4) the finite element analysis correlating observations with test performance.

Design Optimization, Cabling and Stability of Large-Diameter High Jc Nb3Sn Wires

Abstract: In the framework of the High Field Magnets (HFM) program, CERN is developing and qualifying Nb3Sn Rutherford cables to support magnet development towards the requirements of a future energy-frontier collider, using both state-of-the-art commercial wires and experimental wires under development with industrial partners. The trend towards higher current density and larger diameter wires imposes challenges for magneto-thermal stability. In this study, rolling trials and Rutherford cabling have been performed at CERN for two designs of a 1 mm diameter distributed tin Nb3Sn wire produced by KAT, and for 1 mm and 1.1 mm diameter RRP® Nb3Sn wires procured from Bruker OST, and the self-field stability and cabling degradation have been analyzed. The 1 mm RRP® wire shows significant degradation in Ic and stability on cabling. Although the latter is not expected to impact the performance of research magnets, the potential of heat treatment optimization to improve stability has also been quantified. The distributed tin wire shows substantially poorer stability, but promising indications of low cabling degradation. The influence of wire design characteristics on cabling behavior and stability have been assessed, and the implications for future wire optimization towards high field accelerator magnet applications have been discussed.

Conductor Qualification and Fabrication for the MACQU Solenoid

Abstract: A solenoid mock-up called MAdmax Coil for Quench Understanding (MACQU) was designed and tested at CEA Saclay to study the quench propagation in a MAgnetized Disc and Mirror Axion eXperiment (MADMAX) like conductor, i.e., a cable-in-conduit conductor (CICC) with copper conduit cooled at 1.8 K with stagnant superfluid helium. Compared to classic CICCs for fusion magnets, the presence of a cable wrapped by a copper tape and inserted in a copper conduit represented new features from the manufacturing point of view that required a R&D program. In this article, the whole process that led to the final conductor designed for the solenoid MACQU, from strand characterization to the fabrication through the R&D and acceptance phases, is described.

Progress on the R&D for the New Cable-in-Conduit Conductor Type of the MADMAX Dipole

Abstract: The concept of cable-in-conduit conductor (CICC) has been adopted for the large superconducting dipole of the magnetized disc and mirror axion experiment (MADMAX) project. It is based on a multistage cable inserted in a potentially prehardened copper profile and then compacted together down to the final rectangular shape. NbTi technology and internal cooling with stagnant superfluid helium is kept in order to operate at 1.8 K. On the other hand, the use of copper instead of stainless steel as for common CICCs for fusion magnets led to an extensive R&D phase. The need to improve the mechanical properties of the conduit to withstand the high level of mechanical stress in the magnet requires significant level of cold working, which can be obtained by compacting a profile with a large initial cross section. Manufacturing with high compaction over long lengths, within certain tolerances, represented a challenge to find the initial shape of the profile. To deal with it, different compaction scenarios were simulated by finite element methods on two copper profiles eventually manufactured. A mechanical tests campaign aimed to investigate the properties of the processed samples was also carried out. In the present work, the main characteristics of the new MADMAX CICC will be summarized, the R&D phase will be presented, and the results will be widely discussed.

Nb3Sn CIC for Outsert Windings of Hybrid Dipoles

Abstract: A Nb3Sn Cable-in-Conduit (CIC) conductor is being developed for use in the outsert winding of a hybrid dipole for a future hadron collider. The CIC provides several significant benefits for use in a hybrid dipole: Lorentz stress is managed at the cable level, flared ends can be formed with small bend radius with no degradation to the wires within, and supercritical helium cooling flows through the perforated center tube to provide enhanced wire stability. The Nb3Sn outsert is heat-treated as an autonomous assembly, then assembled onto a REBCO insert and preloaded within the dipole yoke structure. The cable and coil technologies of the Nb3Sn CIC are described, and its incorporation in the 18.5 T hybrid dipole is presented.

Failure Mode Effects and Analysis of Superconducting Power Distribution and Related Cryogenic Components for All-Electric Ship

Abstract: Potential failure modes of high temperature superconducting (HTS) devices and related cryogenic systems in electric ship applications are analyzed to understand and plan for the necessary mitigation systems. Risk-based FMEA methodology was adopted to aid in improving the resiliency of large superconducting power distribution systems. A concurrent FMEA study of cryogenic thermal and electrical systems in an HTS power distribution network is discussed. A one-line architecture for a power distribution system was developed to identify the key parameters needed for performing FMEA for HTS power distribution systems. The failure modes are listed to show the interdependence of the electrical and cryogenic systems. The severity and detectability of various failures were used to formulate critical redundancy and mitigation tools to design resilient power distribution systems for electric ships.

Experimental Results of Ultrahigh-Efficiency Wireless Power Transfer Using Extremely High-Quality Factor Superconducting Coil With Double-Sided Coated Conductor Tape

Abstract: Extremely high-quality factor (Q) superconducting coils comprising two conventional high-temperature superconducting (HTS) coated conductor (CC) tapes, the use of which substantially improves the power transfer efficiency (PTE) of resonant coupling wireless power transfer (WPT), have been developed. In this article, a method for joining two HTS CC tapes by using dielectric film tape was developed. A styrene foam coil-support configuration that has lower effective dielectric loss was also developed. The skin effect of the Ag protection layer was suppressed by making it thinner than the conventional one. A coil using the proposed tape had a measured Q (resonant frequency: 8.0 MHz) of around 20 000, which is about 20 times that of one using Cu tape. Measurement of the PTE of a WPT system using coils fabricated using the proposed tape for transmitting and receiving demonstrated that the use of coils with an extremely high Q enables a WPT system to achieve a transfer distance much greater than that of a comparable system with Cu coils. Measured PTE of the system using such coils and one using Cu coils were 90% and 28% at a transfer distance of 80 cm. This achievement opens the door to new high-frequency applications of HTS CC tape such as using if for WPT.

Design and Feasibility Assessment of an HTS Sector Shaped High-Current Conductor for Fusion Coils

Abstract: Technologies based on High Temperature Superconductors (HTS) are evolving rapidly toward maturity. Within the magnetic confinement fusion environment, several projects are demonstrating the possibility to integrate HTS in the coil systems. With respect to Low Temperature Superconducting (LTS) technologies, HTS could allow extending the operating space of fusion coils, either at higher temperatures, or at higher magnetic field levels, and in any case with larger operating margins. Different perspectives and development strategies are proposed, depending on whether HTS is considered a technology to completely substitute LTS, or to integrate and extend its performance range. A fundamental common requirement is the assessment of the layout, the feasibility, and performance demonstration of high-current conductors. Starting from the results achieved with the Al-slotted core cable-in-conduit conductor, and with a view on existing concepts for standard copper and aluminum cables, we have designed a new HTS sector-cable concept, to allow a flexible conductor design and a robust industrial processing. Several trials have been carried out, to verify the manufacturing approach, using either Al- or Cu-based stabilizers. Prototype sub-cables have been characterized at 77 K and self-field, as a necessary step toward the final target of a CICC operating stably with 60 kA at 4.2 K and 18 T, that is presently of interest for the EU-DEMO Central Solenoid Coil.

Electromagnetic Behavior Simulation of REBCO Pancake Coils Considering REBCO Tape Rotation Under High Magnetic Field

Abstract: Since the screening current induced in rare earth-barium-copper-oxide (REBCO) magnet generates an irregular magnetic field, a few screening current simulation methods have been proposed. For an insert REBCO magnet generating ultra-high magnetic field, a new screening current method has been proposed with consideration of the coil-deformation effect. In this article, we have developed a new screening current method based on a partial element equivalent circuit (PEEC) model coupling with a two-dimensional stress finite element analysis to accurately the time-transient distribution of accurate screening current. In the presented method, the changes of self/mutual inductances are considered due to the coil deformation. As the simulation results, it was found that the coil deformation affected the screening current distribution. When considering the coil deformations, the screening current-induced fields to operating current are different for charging cycles. It is necessary to simulate the coil deformation to accurately estimate the screening current and the screening current-induced field.

Impact of Calcium Doping of YBa2Cu3O7-δ Multilayer Thin Films on the Flux Pinning Landscape at 65–5 K, 0–9 T for Various Applications

Abstract: An important research goal in the applications of high temperature superconductor YBa2Cu3O7-δ (YBCO) thin films is increasing both the critical current density and also the isotropic nature of the film. YBCO is inherently anisotropic due to its layered perovskite structure. The critical current density of YBCO thin films is enhanced by increasing the flux pinning sites in the film by the addition of insulating nano-phase materials, such as BaZrO3 (BZO) nanorods, which are also anisotropic in nature. Using a multilayer pulsed laser deposition technique has been shown to produce films with inclusions that are more isotropic in nature. However, the defective BZO nanorod interface, resulting from its lattice mismatch with YBCO, prevents obtaining optimum pinning force. This research explores the effect of Ca doped YBCO space layers in the multilayer composite film, on the BZO nanorod/YBCO interface, over a wide range of conditions of 65–5 K and 0–9T that are suitable for various applications. The interplay of combining these three variables: BaZrO3 addition to YBCO, multilayer film growth resulting from varying pulsed laser deposition conditions, and employing calcium doped YBCO space layers, and the resulting impact on film microstructures and superconducting properties, will be presented.