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  • 1
    Language: English
    In: IEEE transactions on applied superconductivity, 2020-06, Vol.30 (4), p.1-5
    Description: In the framework of the FP7 EuCARD2 project, CEA Saclay developed a cos-theta insert magnet, wound with REBCO high temperature superconductor Roebel cable. Each dipole coil consists of a single arched layer of conductors, insulated with a glass fiber sleeve and impregnated with epoxy resin for mechanical reinforcement. Tooling has been developed to carefully guide the Roebel cable during the winding phase, transfer the coil to the impregnation mold and impregnate it. The magnet is made of two coils assembled around a Nitronic 40 hollow core to mechanically limit its ovalization when operating in a 13 T background field. The structure is completed by the addition of an external stainless steel tube surrounding the coils. This paper details manufacturing tools and fabrication processes validated with stainless steel dummy cable and relates about the fabrication of two superconducting coils. The magnet assembly and preparation for the tests in standalone configuration in INFN-LASA test facility are foreseen for the end of this year.
    Subject(s): Coils ; Superconducting cables ; Accelerator quality magnet ; EuCARD2 ; Windings ; Superconducting magnets ; Cable insulation ; Conductors ; HTS Roebel cable ; superconducting dipole magnet ; Cable shielding
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 2
    Language: English
    In: IEEE transactions on applied superconductivity, 2020-08, Vol.30 (5), p.1-11
    Description: The application of high-temperature superconductors to accelerator magnets for future particle colliders is under study. Numerical methods are crucial for an accurate evaluation of the complex dynamical behavior of the magnets, especially concerning the magnetic field quality and thermal behavior. We present a coupled A-H field formulation for the analysis of magneto-thermal transients in accelerator magnets. The magnetic field strength H accounts for the eddy current problem in the source regions containing the superconducting domains, while the magnetic vector potential A represents the magnetoquasistatic problem in the normal and nonconducting domains. Furthermore, we include a thin-shell approximation for the source regions, making the formulation suitable for large-scale models composed of thousands of tapes. In this article, the relevant equations are derived and discussed, with emphasis on the coupling conditions. The weak formulation is derived, and numerical results are provided in order to both verify the formulation and scale it to the size of an accelerator magnet.
    Subject(s): High-temperature superconductors ; finite-element analysis ; magnetic fields ; magnetization ; Windings ; Superconducting magnets ; Conductivity ; superconducting coils ; Magnetic separation ; Magnetic domains ; eddy currents ; Mathematical model ; Accelerator magnets
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 3
    Language: English
    In: IEEE transactions on applied superconductivity, 2019-08, Vol.29 (5), p.1-4
    Description: The short-sample critical current is only an indicative property for the maximum current a magnet can be continuously operated with. This was especially visible in the experiments of one of the world's first Roebel-cable-based high temperature superconductors dipole magnet prototype built and tested at CERN in 2017 where the thermal runaway developed very slowly in many cases. Consequently, the maximum stable operation current could be overstepped and stable operation could be recovered by lowering the current below the maximum of the stable range again. It is non-trivial to quantitatively predict this behavior from the critical current measurements which are observed under specific cooling conditions and based on an arbitrarily selected electric field criterion for the critical current. To make more rigorous predictions on the maximum stable operation current, one needs to consider in detail the interplay of cooling over the magnet surface and heat generation in the winding. This paper presents a methodology to determine the maximum stable operation current for a given magnet, as well as studies its mathematical background. Insight to this problem comes from the Roebel-cable-based dipole magnet studied at CERN during 2017.
    Subject(s): Heating systems ; High-temperature superconductors ; Cooling ; modeling ; Computational modeling ; finite element methods ; optimization ; Magnetic domains ; Superconducting magnets ; HTS magnets ; Thermal stability
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 4
    Language: English
    In: IEEE transactions on applied superconductivity, 2018-04, Vol.28 (3), p.1-10
    Description: The EuCARD2 collaboration aims at the development of a 10 kA-class superconducting, high current density cable suitable for accelerator magnets, to be tested in small coils and magnets capable to deliver 3-5 T when energized in stand-alone mode, and 15-18 T when inserted in a 12-13 T background magnet. REBCO tape, assembled in a Roebel cable, was selected as conductor. The developed REBCO tape has reached a record engineering critical current density, at 4.2 K and 18 T of 956 A/mm 2 . Roebel cable carried up to 13 kA at 20 K when tested in a small coil (FeatherM0.4). Then a first dipole magnet, wound with two low-grade Roebel cables of 25 m each, was assembled and tested. The dipole reached the short sample critical current of 6 kA generating more than 3 T central field at about 5.7 K, with indications of good current transfer among cable strands and of relatively soft transition. The construction of a costheta dipole is also discussed. Eucard2 is reaching its objective and is continuing with the H2020-ARIES program aiming at doubling the Je at 20 T to obtain 6 T as standalone and 18 T as insert in a high field facility.
    Subject(s): Coils ; High-temperature superconductors ; accelerator magnets ; Critical current density (superconductivity) ; Collaboration ; HTS dipoles ; Superconducting magnets ; Conductors ; HTS conductor ; Condensed Matter Physics ; Electrical and Electronic Engineering ; Electronic, Optical and Magnetic Materials
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 5
    Language: English
    In: IEEE transactions on applied superconductivity, 2019-08, Vol.29 (5), p.1-8
    Description: Very high electromagnetic forces are generated in the superconducting coils of high field accelerator magnets. The cables, which are used to wind the coils, can withstand limited pressure levels and strains generated during the powering without degradation. To protect the cables from mechanical damage, reliable prediction of strain and stress inside the coil is paramount for designing suitable support structure of the magnet. This is naturally done before a magnet is built and tested, which emphasizes the need for reliable modeling. Conventionally, the mechanics in superconducting coils are modeled assuming homogenized material properties inside a homogenized coil volume. Using this so-called coil block approach, predicting the actual cable strain or stress inside the homogenized volume is unreliable. In order to predict reliably the stress in the cable, more detailed representation of the modeling domain is needed. This paper presents a workflow to perform a detailed mechanical analysis using finite-element analysis following the envisioned and more detailed approach. As an example, a high field 20 T+ magnet with clover leaf ends is studied, and results are discussed. The results reveal considerable difference between the behavior of modeled homogenized coil blocks and coils where turns are individually considered.
    Subject(s): Coils ; Solid modeling ; quadrupoles ; modeling ; Magnetomechanical effects ; correctors ; simulation ; Superconducting magnets ; Stress ; Strain ; superconducting magnet mechanical factors ; finite element methods ; magnet supports ; Magnetic domains ; computer aided engineering ; magnet structure ; Accelerator magnets: dipoles ; HTS magnets
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 6
    Language: English
    In: IEEE transactions on applied superconductivity, 2019-08, Vol.29 (5), p.1-5
    Description: In the frame of the high-luminosity upgrade project for the large hadron collider, new twin aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These magnets are 2.2 m long canted cosine theta NbTi dipoles, with two independently powered apertures oriented such that their field vectors are perpendicular to each other and to the direction of the beams. A 0.5 m model magnet in single and double aperture configuration and a full-length double aperture prototype were built and tested at CERN. In this paper, the performance of these magnets at 1.9 K in terms of training behavior, quench detection and protection, and other tests is discussed. In addition, the thermal response of the magnet to a hypothetical beam discharge is simulated and analyzed.
    Subject(s): Temperature measurement ; Resistors ; quench ; Current measurement ; CCT ; Prototypes ; Superconducting magnets ; Apertures ; NbTi ; Magnetic tunneling
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 7
    Language: English
    In: IEEE transactions on applied superconductivity, 2015-12, Vol.25 (6), p.1-5
    Description: Due to the wide spectrum of current sharing temperatures in a high-temperature superconducting (HTS) magnet, estimating the energy required to quench the magnet is a complicated task. On the other hand, quenching a low-temperature superconducting (LTS) magnet for quench characterization purposes with a heater is straightforward due to the small temperature margin and correspondingly low minimum quench energy (MQE). To estimate the required energy for the LTS magnet, the analytical concept of MQE can be utilized. In this paper, we propose that only numerical simulations can give adequate estimates to the MQE of an HTS magnet, for measurement purposes. Furthermore, due to the high enthalpy margin, the utilization of spot heaters with short energy pulses becomes questionable. We present in detail the effect of heater's pulselength to the MQE, when a strip heater is utilized for quenching. In addition, the effect of the heater area on MQE is studied. We consider the model of a REBCO coil to be constructed and tested in the Enhanced European Coordination for Accelerator Research and Development (EuCARD-2) Project. According to the results: 1) MQE increases almost linearly for pulselengths between 100 and 500 ms; 2) when the heater area is enlarged, the required energy per area saturates to a certain value related to the coil's enthalpy margin; 3) MQE obtained with a traditional analytic approach based on a minimum propagating zone considerably underestimates the numerically obtained MQE.
    Subject(s): High-temperature superconductors ; high temperature superconductors ; quench simulation ; super conducting magnets ; Superconducting magnets ; Stability analysis ; minimum quench energy ; High temperature superconductivity ; Research ; Metals ; Methods ; Quenching
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 8
    Language: English
    In: IEEE transactions on applied superconductivity, 2016-06, Vol.26 (4), p.1-8
    Description: An investigation is performed on the quench behavior of a conceptual 50-GJ 8-T high-temperature-superconductor-based solenoid. In this design, a 50-kA conductor-on-round-core cable-in-conduit conductor utilizing ReBCO technology is envisioned, operating at 40 K. Various properties such as resistivity, thermal conductivity, and heat capacity are very different at this temperature, which affects the quench behavior. It is found that the envisioned conductor is very stable with a minimum quench energy of about 2 kJ. However, the quench propagation velocity is typically about 20 mm/s, so that creating a wide-spread normal zone throughout the coil is very challenging. Moreover, an extraction voltage exceeding 20 kV would be required to ensure a hot-spot temperature below 100 K once a thermal runaway occurs. A novel concept dubbed "rapid quench transformation" is proposed whereby the superconducting conductor is co-wound with a normal conductor to achieve a high degree of inductive coupling. This geometry allows for a significant electric noise reduction, thus enabling low-threshold quench detection. The secondary circuit is connected in series with a stack of diodes, not allowing current transfer during regular operation, but very fast current transfer once a quench is detected. With this approach, the hot-spot temperature can be kept within 20 K of the cold mass temperature at all times, the hot-spot temperature is well below 100 K, and just under 80% of the stored energy can be extracted during a quench.
    Subject(s): Geometry ; Critical current density (superconductivity) ; Power cables ; Superconducting magnets ; Conductors ; Thermal conductivity ; Cable shielding
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 9
    Language: English
    In: IEEE transactions on applied superconductivity, 2019-01, Vol.29 (1), p.1-8
    Description: For reaching very high magnetic fields in fully superconducting magnets, beyond 16 T for particle accelerators dipoles and beyond 23 T for solenoids, the use of high-temperature superconductors (HTS) is unavoidable. Due to the high minimum quench energy in HTS these coils are much more difficult to protect against quenches using conventional methods, such as quench heaters or coupling loss induced quench (CLIQ). Although it is possible to use a dump resistor on a short HTS magnet, extracting the energy externally, this does not provide a solution for longer magnets or magnets operated in a string, because the extraction voltage becomes unacceptably high. Here, a method named E 3 SPreSSO (External Energy Extraction Symbiotic Protection System for Series Operation) is proposed that allows for fast energy extraction in HTS magnets. The E 3 SPreSSO comprises of units with a near-zero self-inductance superconducting circuit, connected in series with the main magnet. When the protection is triggered, these devices are turned resistive, using quench heaters, overcurrent or CLIQ, causing them to absorb the energy of the system. The units can be located outside the main magnet and do not generate magnetic field. Therefore, it is possible to use relatively cost-efficient and robust Nb-Ti or possibly MgB 2 (at higher temperatures). This paper introduces the concept and provides an analytical method weighing the different options for designing the E 3 SPreSSO units themselves.
    Subject(s): Coils ; Resistance ; Heating systems ; Resistors ; High-temperature superconductors ; quench protection ; Superconducting magnets ; High-temperature-superconductors (HTS) ; Magnetic circuits ; switch
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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  • 10
    Language: English
    In: IEEE transactions on applied superconductivity, 2020-06, Vol.30 (4), p.1-5
    Description: Hadron and proton therapy are cutting edge techniques for cancer treatment and a great development of specialized medical centers and research facilities is foreseen in the next decades. One of the main obstacles to the penetration of the use of charged particles for therapy is the construction of complex and expensive accelerating structures and rotating transfer lines, i.e., gantries, able to bend and focus the beam down to the patient. GaToroid is a novel concept of a fixed toroidal gantry, able to deliver the dose at discrete angles in the whole range of treatment energies in steady-state configuration. The steady-state current and magnetic field are appealing features, implying simplified demands on stability, powering, mechanics and cooling, as well as for the clinical perspective, allowing rapid variations of beam energy and treatment angle. In this work, we present the magnetic design of the toroidal coils composing the first instance of GaToroid, focusing the analysis on an option for a proton machine with an energy range of 70 MeV to 250 MeV. To create a proper magnetic field distribution, the coils have been designed with peculiar asymmetric shape and the windings have been graded. An initial winding geometry was obtained with an optimization aiming at maximum energy acceptance of the gantry. We are now progressing to the detailed engineering design. We describe here the overall magnet design, coil and conductor layout (LTS and HTS options), and mechanical studies involving the general torus structure. Quench protection is evaluated for LTS (Nb-Ti) configuration, as well as more innovative HTS (ReBCO) options. Finally, we present the design and the construction of a scaled-down demonstrator, intended as the proof of principle of winding procedure and mechanical coil structure.
    Subject(s): Coils ; Protons ; Hadron Therapy ; High-temperature superconductors ; Toroidal Magnets ; Gantry ; Toroidal magnetic fields ; Medical treatment ; Superconducting magnets ; Conductors ; Magnet Design ; Superconducting Coils
    ISSN: 1051-8223
    E-ISSN: 1558-2515
    Source: IEEE Electronic Library (IEL)
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