Gijs de Rijk

The Astroparticle Research Compact Orbital Spectrometer (ARCOS) magnet is a 12-coil toroidal magnet for a proposed next-generation magnetic spectrometer in space. AMaSED-2 is a small-scale non-flight demonstrator coil for the ARCOS magnet. AMaSED-2 consists of two individually built no-insulation high-temperature superconducting pancake coils with racetrack-like shapes. The two pancake coils are contained in a total of 724 m of 12 m m wide SuperPower REBCO HTS tape. Copper bands functioning as current leads and layer jump surround the winding blocks. An aluminum structure mechanically supports the coil assemblies. AMaSED-2 was manufactured and tested at CERN. The coil was tested in cryogenic helium gas at various temperatures between 10 K and 77 K by measuring the center magnetic flux density while varying the operating current. We employ a model for no-insulation coils and identify for each temperature the center magnet constant and magnet charging time constant as system parameters. We also determine the radial resistance, peak magnet constant, magnet critical current, and maximum achieved magnetic flux densities. Central magnetic flux densities up to 2.9 T were measured, corresponding to a peak magnetic flux density on the coil of 9.7 T . The design and characterization of AMaSED-2 provides a basis for future magnet development of a flight model.

Magnetic spectrometers detect the rigidity of charged particles by measuring the bending of their trajectories as they pass through a magnetic field. ARCOS is a proposal for a next generation magnetic spectrometer in space with a bending strength of 3 T $\,$ m at an operating temperature of 20 K. ARCOS is based on a 12-coil toroidal HTS magnet. Within the HTS Demonstrator Magnet for Space (HDMS) project, we have designed and built AMaSED-2, a small-scale demonstrator coil for the ARCOS magnet. AMaSED-2 consists of two individually built no-insulation HTS ReBCO pancake coils with racetrack-like shapes. The exclusion of electrical insulation material between adjacent winding turns enables self-protection against quenches. The winding blocks are surrounded by copper bands functioning as current leads and layer jumps. AMaSED-2 is supported by a lightweight mechanical structure made from aluminum alloy. We describe the design of AMaSED-2 and present a simple mathematical circuit model for no-insulation coils.

The design and construction of compact and lightweight gantries for hadron therapy are essential steps toward wider accessibility to this cancer treatment. The use of a high-field steady-state toroidal gantry, i.e., GaToroid, represents an attractive alternative to the state-of-the-art with the potential of significantly reducing size and weight of present installations. It is interesting to conceive the use of High-Temperature Superconductors (HTS) conductors to reach magnetic fields beyond 8 T at relatively high temperatures, decreasing the beam bending radius and, at the same time, avoiding complex cryogenics systems in the hospitals. The construction of such a machine requires several steps of prototyping and this manuscript presents the design of the first GaToroid single-coil demonstrator, wound with ReBCO conductors. The demonstrator is a scaled version of a full-scale GaToroid coil, with the conductors spaced into four planar windings, i.e., grades, and wound as a double pancake. Two operating regimes are foreseen to test the demonstrator at different temperatures, currents and magnetic fields. The cable geometry, composed of four ReBCO non-twisted tapes, was validated through 1D quench propagation studies in both regimes, and the hot spot temperature is well below 100 K. Furthermore, three-dimensional mechanical simulations allowed to estimate the stress state on the conductor, as well as to define the impregnation strategy of the demonstrator. The answers provided by the manufacturing, powering and test of the proposed demonstrator can provide valuable insights for the future construction of full-scale GaToroid coils.

The upgraded magnet assembly of the EDIPO test facility aims at generating 15 T at 4.2 K and 85% of short sample limit in a large rectangular aperture and over a uniform field length of 1000 mm. During 2020 the design studies have concentrated on two flared-end block-coil design options with four double-pancake coils, two per pole. The coils are planned to be produced using Nb3Sn Rutherford cable with 44 × 1.1 mm diameter strands, which results in significantly larger dimensions compared to the typical cables used in accelerator magnets. Two sections of dummy superconducting cable have been produced, and dedicated tooling was developed to study the wind-ability of such high aspect ratio cable and provide input to define the geometrical parameters of the coil flared ends. This paper describes two magnet designs proposed for EDIPO focusing on the magnetic and the mechanical design.

In 2018, FRESCA2 magnet, developed within a collaboration be-tween CEA and CERN to provide a background field for tests of cables and small coils, reached a field of 14.6 T. This represents a new record field for dipole magnets with a clear aperture. As a continuity of the European project EUCARD-2, CERN aims at exploring accelerator magnet technology up to a 20 T operating field level. For that aim, Feather magnet 2, coils 3 and 4 (FM2.3-4) utilizing REBCO Roebel cable is planned to be inserted in FRESCA2 to reach a higher field. A new structure must be de-signed to accommodate the insert coils inside FRESCA2. The in-tegrated design has to be capable to deal with several challenges. The magnetic forces in the coils of the insert magnet are high. FRESCA2 is pre-loaded by the so-called bladder-and-key con-cept, and a shrinking Al-alloy shell. The preload, however, de-creases the diameter of the aperture at cryogenic temperature. The stiff external tube of FM2.3-4 is specifically designed for the background field operation. This component, made of 3D printed Inconel-based alloy, has a different thermal contraction with re-spect to the inner pole of FRESCA2. As a result, the thickness of the shell of FM2.3-4 needs to be maximized to guarantee mechan-ical support for the FM2.3-4, while simultaneously enabling the integration with FRESCA2.

In 2018, two structures have been proposed with the goal of re-placing the magnet EDIPO that stopped operating in 2016. These two solutions were designed to generate a field of 15 T on an aperture of 100x150 mm2 at 4.2 K by using Nb3Sn super-conducting Rutherford cable. After the boarding review, which took place in December 2018, a solution consisting of 6-double-layers coils was retained, based on the 2-D modelling results. We now extend the study, by considering the 3-D models, with the goal of concluding the magnet conceptual design. The target is to obtain a homogeneous field, with 1% of homogeneity, over a length of 1000 mm, which allows the testing of superconduct-ing cables for both fusion and high-energy physics. The double-layers coils, of the block-type magnet, have flared ends to allow the aperture to cross the magnet length. The 6-coils solution differs from previous similar projects as the FRESCA2 and HD2 magnets, where 4-coils were used

In the frame of a collaboration between CERN, ASI, University of Trento, and TIFPA, the HTS demonstrator magnet for space project has started to define methods and procedures for manufacturing high temperature superconducting magnets for space applications. To this purpose, we developed a conceptual design of a superconducting magnetic spectrometer for a physics experiment in space. The configuration is a toroid with twelve superconducting coils based on ReBCO tape. By using ReBCO tape with an engineering critical current density, J _e, exceeding 1000 A mm⁻² at 4.2 K and 20 T , as reached in the H2020-ARIES program, the magnet system provides an average bending strength of 3 T m . This is sufficient to measure charged particles with rigidities up to 100 TV , more than two orders of magnitude higher than the present state-of-the-art space spectrometer. The magnet system requires about 62 km of 12 mm ReBCO tape and produces a peak magnetic field of 11.9 T at an operating temperature of 20 K . A small scale single coil, which is about one third in size of a coil from the toroidal magnet system, will be manufactured and tested as demonstrator of the magnet technology. The mechanical structure and performance of the toroidal magnet system and demonstrator coil are described.