Magnetic determination of the current center line for the superconducting ITER TF coils

The ITER tokamak includes 18 superconducting D-shaped toroidal field (TF) coils. Unavoidable shape deformations as well as assembly errors will lead to error fields in the final configuration, which can be modeled with the knowledge of the current center line (CCL). We are building a room temperature magnetic measurement system using low frequency ac excitation current through the TF coil and arrays of pick-up coils, fabricated with printed circuit board technology. Deviations from the expected shape of the CCL will be obtained by comparing the amplitude of magnetic flux measured at several locations around the perimeter of the TF coil, with values computed assuming the nominal current distribution. We present experimental results obtained with a cable placed in one turn groove of a full scale radial plate.peer-reviewe

Design and Beam Dynamics Studies of a Novel Compact Recoil Separator Ring for Nuclear Research with Radioactive Beams

The recent development of radioactive beam facilities has significantly expanded the capabilities for investigating the structure of the atomic nucleus and the nuclear interaction. For instance, the HIE-ISOLDE facility at CERN delivers presently the largest range of low-energy radioactive beam available worldwide. This energy range is ideal for the study of nuclear structure, low-energy dynamics and astrophysics by using nucleon transfer, Coulomb excitation and deep inelastic reactions. All these studies require an efficient and high-resolution recoil separator for the clear identification of medium and large mass reaction fragments. To meet these needs, we propose a versatile recoil separator for radioisotopes based on a compact storage ring, the Isolde Superconducting Recoil Separator (ISRS) formed of superconducting combined-function nested magnets with both, bending and focusing/defocusing functions. The ISRS is designed to operate in high momentum acceptance and isochronous modes. In this paper, we present the optics design and detailed beam dynamics studies for the performance characterisation

Mechanical Characterization of Nb3Sn Cable Insulation Systems Used for HL-LHC Accelerator Magnets at Ambient Temperature

The performance of accelerator magnets is strongly relying on the dielectric strength and mechanical robustness of the insulation system. This is in particular relevant for the current development of high field superconducting Nb 3 Sn magnets with the insulation system made from resin-impregnated glass fibres. During the assembly and operation at cold temperature, this insulation system is exposed to high mechanical compressive and shear stresses. The focus of the study was the investigation of the mechanical shear strength of the insulation composite. The experimental tests have been performed at room temperature, determining the mechanical strength and the failure mechanisms of the cable insulation system. Within this test the inter-laminar shear strength (ILSS) and non-standardized combined shear compressive strength were determined. The test sample preparation was based on the manufacturing procedures and materials used in the series fabrication for the CERN HL-LHC Nb 3 Sn coils. The individual insulation systems are varying in the S2-glass yarn density, the sizing, and the fibre volume fraction. Furthermore, the presence of mica insulation on the mechanical strength has also been studied. This paper describes the applied measurement procedures used during the test campaign, and presents the relevant measurement results, identifying the mechanical limitations of the insulation system

Room Temperature Magnetic Determination of the Current Center Line for the ITER TF Coils

The ITER tokamak includes 18 superconducting D-shaped toroidal field (IT) coils. Unavoidable shape deformations as well as assembly errors will lead to field errors, which can be modeled with the knowledge of the current center line (CCL). Accurate survey during the entire manufacturing and assembly process, including transfer of survey points, is complex. In order to increase the level of confidence, a room temperature magnetic measurement of the CCL on assembled and closed winding packs is foreseen, prior to insertion into their cold case. In this contribution, we discuss the principle of the CCL determination and present a low frequency ac measurement system under development at PSI, within an ITER framework contract. The largest current allowed to flow in the TF coil at room temperature and the precision requirements for the determination of the CCL loci of the coil are hard boundaries. Eddy currents in the radial plates, the winding pack enclosures, and possibly from iron in the reinforced concrete floor of the assembly hall are more subtle to bring under control quantitatively, and will limit the highest frequency that can be used to measure reliable values of the field gradients. Our objective is to measure the CCL loci by combining magnetic data obtained with printed circuit board flux coils and survey data gathered around the perimeter of the D-shaped coil

Development of a Short Model of the Superconducting Separation Dipoles D2 for the High Luminosity Upgrade of LHC

The luminosity upgrade of the Large Hadron Collider requires that the new separation/recombination dipoles D2 deliver a field integral of 35 Tm. A design has been developed of a twin dipole generating a magnetic field as high as 4.5 T in apertures of 105-mm and 7.78-m magnetic length. The magnetic field direction is identical in both apertures causing not negligible magnetic cross talk, which could be highly detrimental for the field quality. In order to minimize the cross talk effects a design based on asymmetric coils has been developed in the past years. Recently, the design has achieved a level of maturity allowing the starting of a second phase of development involving the construction of a short model preliminary to prototyping activities. The short model (1.6-m long) has been designed in all aspects and it is presently under construction in industry. The contribution is focused on the design of the short model with emphasis on the mechanical aspects, which includes a novel approach to the integration of coils in the mechanical structure through the use of Al-alloy sleeves

Frequency-Domain Diagnosis Methods for Quality Assessment of Nb3_{3}Sn Coil Insulation Systems and Impedance Measurement

In recent years, the superconducting Nb$_{3}$Sn cable material became the privileged mature candidate for the high-field magnets in new projects like high-luminosity LHC (HL-LHC) accelerator at CERN, Geneva, Switzerland. The technology in 2017-2021 needs to be deployed through an unprecedented magnet series production with dedicated online quality control. The key fabrication stage of the vacuum pressure impregnation (VPI) after the heat treatment reaction of Nb$_{3}$Sn coils, as on the new 11-T dispersion region dipole, enhances both the structural integrity and the dielectric strength of the winding packs. The global vacuum impregnation pressure method exhibits various merits in insulation performance and high dielectric strength reliability, which is strongly dependent on the success of the resin filling cycle. This online capacitive measurement method enables one to derive comparative master trend curves of various impregnated coils and possibly optimize the curing cycle. Ultimately, a combination of the above methods with a dielectric frequency response can bring insights on the impregnation process, the impacts from the resin choice and insulation material quality on the degree of curing, and the coil assembly geometry. The frequency impedance measurement of the first short dipole models DP101-102 provides the distributed lumped circuit fitting electrical parameters for the transient characterization of produced magnets