Speaker
Description
High Temperature Superconductors (HTS) offer significant potential for very high field dipole. We started the development of REBCO-insulated dipole magnetsin 2010 with EUCARD and EUCARD2 programs. CEA Paris-Saclay then chose to apply the Metal-as-Insulation (MI) REBCO winding, originally developed in the 32.5 T solenoid insert project NOUGAT, the design, fabrication and tests of HTS high field dipoles. These new developments started in 2023 through the support of a CERN-CEA collaboration in the framework of High Field Magnet (HFM) CERN program. It is the first step toward a 14 T+ HTS dipole magnet for accelerator machines.
The development strategy is to start with small and simple coils to validate the numerical design models, and then increase gradually the complexity and risks. In this regard, we began by modelling and studying the racetrack coil shape. This configuration offers the advantages of planar winding and therefore does not require hardway bending. This kind of geometry is therefore easily transferable from the pancake solenoid coils. The MI approach is also well suited for testing models limits because it allows for very compact coils. Additionally, despite the higher complexity of numerical models, MI coils present lower degradation risks compared to its insulated counterpart during testing. Over the past two years, we focused on developing the tools for making MI racetrack coils. This includes numerical tools for MI racetrack coils design, as well as tooling, and winding procedures. We have also focused on the design of mechanical structures, including the cooling aspects, the stresses management, and the assembly of multi racetracks coils. Recently, we fabricated and tested the first two mockup racetracks coils in 140 mm and 600 mm straight part length versions With a 30 mm width mandrel. These tests were conducted in a self-field configuration, at liquid nitrogen temperature for both coil lengths and at liquid helium temperature only for the shortest coils.
After a brief description of the program’s philosophy and strategy, this presentation will detail the design, fabrication, assembly and test of two racetracks. We will also discuss the lessons learned from measurements at current density above 1500 A/mm² and the results regarding the design and numerical evaluations. One major aspect is the high magnetization effect that can lead to a lower critical current than expected even for 4 mm-wide REBCO tape. This is due to very high local current densities and related magnetic stresses.
This work was supported by CERN-CEA Collaboration Agreement under Grant HFM/KE5647/TE
