The next generation of high-field magnets for accelerators relies on Nb 3 Sn conductors, mostly Rutherford-type cables. Superconducting cables are anisotropic composites structures that can comprise ...strands, impregnation and insulation wrapping materials. Moreover, Rutherford cables are characterized by a multi-scale architecture going from the micron-size sub-elements to meter-size coils. Due to the mechanical sensitivity of the Nb 3 Sn material, the sub-element behavior drives the performance of the magnet. To predict and improve the performance and behavior of the magnets, numerical modeling is now crucial. The multi-physic and multi-axial loadings, the complex multi-scale structure and the intrinsic properties of the Nb 3 Sn material require three-dimensional models to be able to understand and represent the different phenomena. A tool that is able to generate 3D Finite Element (FE) model of a Rutherford cable has been developed at CEA over the last years in the framework of the CoCaSCOPE approach. It allows generating a meshed FE model from the main cable parameters (size, number of strands, etc.) and usable with multi-physic simulation software. This paper presents the different steps to construct the geometry of the cable, and the main features of the mesh. Techniques to model different configurations are presented, considering the stainless-steel core and/or a keystoned shape. Today, the CoCaSCOPE mesh generator (CoCaSCOPE-MG) is open to the scientific community. The authors propose to generate any type of Rutherford cable on demand.
The quench protection for the Future Circular Collider (FCC) 16 T Nb 3 Sn dipoles was based either on the CLIQ (Coupling Loss Induced Quench) system, or on resistive quench protection heaters. ...Several heater designs were sketched during the iterative magnet design processes. This led to identifying some rules about an effective heater design in the full-scale 14-m-long magnets. Following the FCC study, short dipole magnet models are being built to test the novel features that were envisioned for the FCC magnets. In this work, we review the principles of effective heater design, and then apply this methodology to the graded block dipole short model R2D2, which is being designed at CEA Saclay. This magnet has high current density in copper after quench, which makes the protection challenging and requires pushing the heater technology to its limits.
Future high energy particle colliders are under study, with a first goal of 16 T dipoles, which is believed to be the practical limit of Nb 3 Sn magnets. Another more ambitious goal is to aim for 20 ...T dipoles. This very high field would require High Temperature Superconductors (HTS), such as Bi2212 or REBCO. Their substantially higher cost necessitate anyways the use of Nb 3 Sn for an affordable accelerator application. Therefore, hybrid designs can be proposed, where the HTS are used in the high field (16-20 T) area, and Nb 3 Sn are used in the low field (<16T) area. Rectangular block-coil designs are particularly well adapted to this concept, since the separation between high field and low field can be made parallel to the cable turns, inside each layer of the coil. However, the large forces accumulating on the cable turns generate a high transverse stress detrimental to the coil. The paper presents a conceptual Hybrid Nb 3 Sn-HTS design generating 20 T in the bore with margin, using a block-coil concept. Several conductor options are discussed. The design also proposes stress-management solutions to deal with the large stress developing in the coils.
Superconducting magnets are crucial components in various scientific, industrial, and medical applications, offering unparalleled high magnetic fields and energy efficiency. However, the transition ...from the superconducting to the normal state, known as a quench, can pose significant challenges due to the sudden local release of stored energy and damage to the magnet system. Quench protection strategies have emerged as essential mechanisms to mitigate the adverse effects of quenches. One of the commonly used methods in accelerator magnets is to use strip heaters on coil surfaces. The heater element length and configuration influence the performance of the quench protection. The study of the quench protection by heaters requires the coupled modelling of the Joule heating, normal zone propagation, and transferring heat from the heaters to the cable. In this article, we present a new 2D finite element simulation model to model the increase of the cable resistance under different heater lengths in Nb 3 Sn accelerator magnets. The model allows analyzing heaters with several different lengths of heating stations along the cable. This strategy can be used to maximize the cable resistance increase at high operation current while still providing the needed normal zone propagation at lower currents. We demonstrate the model use with a high-field racetrack dipole model.
Towards 20 T Hybrid Accelerator Dipole Magnets Ferracin, P.; Ambrosio, G.; Arbelaez, D. ...
IEEE transactions on applied superconductivity,
09/2022, Letnik:
32, Številka:
6
Journal Article
Recenzirano
Odprti dostop
The most effective way to achieve very high collision energies in a circular particle accelerator is to maximize the field strength of the main bending dipoles. In dipole magnets using Nb-Ti ...superconductor the practical field limit is considered to be 8-9 T. When Nb 3 Sn superconductor material is utilized, a field level of 15-16 T can be achieved. To further push the magnetic field beyond the Nb 3 Sn limits, High Temperature Superconductors (HTS) need to be considered in the magnet design. The most promising HTS materials for particle accelerator magnets are Bi2212 and REBCO. However, their outstanding performance comes with a significantly higher cost. Therefore, an economically viable option towards 20 T dipole magnets could consist in an "hybrid" solution, where both HTS and Nb 3 Sn materials are used. We discuss in this paper preliminary conceptual designs of various 20 T hybrid magnet concepts. After the definition of the overall design criteria, the coil dimensions and parameters are investigated with finite element models based on simple sector coils. Preliminary 2D cross-section computation results are then presented and three main layouts compared: cos-theta, block, and common-coil. Both traditional designs and more advanced stress-management options are considered.
R2D2, the Research Racetrack Dipole Demonstrator, is a short model being developed within a collaboration between CEA Paris-Saclay and CERN. The goal of the program is to develop key technologies for ...future high field 16 T Nb3Sn magnets for particle colliders. In the particular case of block-coil designs, two different cable grades are wound in the same coil layer, in order to maximize the current density, therefore to minimize the size of the magnet and the use of superconductor. One of the most challenging technologies with this grading concept, is the connection between two cables grades. CEA Paris-Saclay has proposed a concept of external joints, for which the cable exits are guided outside of the coil to perform the connections between the cable grades. The R2D2 project is aimed at demonstrating this technology in a representative demonstrator magnet, while simplifying and reducing the risks when possible, as an intermediate step towards 16 T magnets. In particular, the magnet is composed of single-layer racetrack coils, mainly to reduce the use of conductor and simplify some fabrication steps. However, the complexity inherent to the external joints requires a special focus in the design of the coil ends. To do so, the design of the magnet has been performed using a combination of CAD (Computer Aided Design), magnetic and mechanical 3D FEM (Finite-Elements Models). This paper will explain the design choices leading to a safe operation of the magnet in terms of peak fields and peak stresses.
ASTERICS is an Electron Cyclotron Resonance (ECR) ion source designed by CEA, GANIL, and LPSC for the NEWGAIN project in France. The design of the Nb-Ti superconducting magnet is inspired from two ...magnets built for 28 GHz ion sources (VENUS and FRIB ion sources) and is composed of a sextupole inside three solenoids to confine the plasma. The main improvement in terms of magnetic design comes from an increase of the plasma chamber radius from 71.85 mm to 91 mm aiming at increasing the metallic beam yield at both 18 and 28 GHz. This change in magnetic design leads to an increase of Lorentz forces, impacting the design of the mechanical structure. Like the FRIB ion source, the architecture uses an aluminum shell-based support structure with bladders and keys to compress the sextupole azimuthally, and endplates for its axial compression. The bladders and keys allow a disassembly of the sextupole coils, and an adjustment of the coils pre-stress. The solenoids are wound under tension around an aluminum mandrel acting as a shell for the sextupole pre-load. Interfaces between solenoids and mandrel are designed to allow detachment and low friction sliding during excitation. The scale-up of the support structure, to address the dimension increase, is presented here. The 2D and 3D mechanical models developed to perform the mechanical analysis and the results obtained are detailed along with the preliminary assembly process.
In the framework of the NEWGAIN project, which aims to build a second injector with a mass to charge-state ratio A/q=7 for the SPIRAL2 linear accelerator at GANIL, CEA is developing in collaboration ...with LPSC and GANIL a new superconducting 28 GHz ECR Ion Source Magnet named ASTERICS. The magnetic design is based on an advanced concept of the VENUS ECR ion source operating at Berkeley and the FRIB source under commisionning at MSU. The ion source superconducting magnet consists of a sextupole inside three solenoids to confine the plasma and a shell-based support structure to apply a preload to the sextupole coils. The confinement coils will be made in Nb-Ti and will be operated at 4.2 K. The cryogenic environment will be ensured by liquid helium thermosiphon closed loop thanks to six in-situ cryocoolers. Specific HTS current leads are being designed to power the magnet. A cold integrated He buffer will also allow He almost-lossless quenches. The preliminary design choices of the ASTERICS superconducting magnet are presented here from the magnetic, mechanical and protection design to the cryogenic definition emphasizing the global approach used to obtain the final magnet configuration.
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 Nb 3 Sn 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 Nb 3 Sn 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.
