Anna Stampfli

High-temperature superconducting (HTS) cables of fer a promising opportunity for high-field magnet applications. However, the exact technology stack that would lead to accelerator-quality magnets is as yet not consolidated. A vigorous design-build-test cycle is required to evaluate the potential of different approaches. To implement such program at PSI, in the framework of the CHART initiative, we propose using the same magnet geometry previously tested with an LTS stress-managed magnet while replacing the rectangular Nb3Sn Rutherford cables with HTS straight soldered stack cables– a design that seamlessly integrates into the existing structure. Currently, we are in the design and process-development stage, with testing planned for later in 2025. This study presents magnetic field-quality estimation and AC loss computations for the HTS common coils magnet, based on finite element method (FEM) modeling of the final magnet design. The study includes an estimation of the required stabilizer content for protection with dump resistor at a maximum applied current of 10 kA, as well as the design of internal and external joints. Additionally, a novel coil winding technique enables simultaneous winding, insulation, and soldering of the cable, thus, overcoming the tape-stack cable's low minimal bending radius and offering scalability for larger magnet applications. This work represents a possible way for the practical application of HTS cables in accelerator magnets. A direct benchmark against LTS cables in identical geometry provides valuable insights and a faster path-way to experimental results and model validation.

The Magnet Development (MagDev) laboratory at the Paul Scherrer Institute (PSI) has designed and successfully manufactured the first subscale stress-managed common coil magnet. The magnet was tested at CERN and reached 98% of its short sample current at 4.5 K. Following the high-field magnet roadmap of the Swiss Accelerator Research and Technology initiative (CHART), a new magnet was assembled after replacing two of the four Nb₃Sn coils and manufacturing and integrating four copper-based coils, which are part of the Energy Shift with Coupling (ESC) quench protection method. The ESC system uses normal-conducting auxiliary coils that are strongly magnetically coupled with the magnet’s Nb₃Sn coils for protection. When a quench is detected, a current is discharged through the auxiliary coils, leading to a rapid transfer of the magnet’s energy from the Nb₃Sn coils to the copper-based coils. This process results in transient losses and quick transition to the normal state of the Nb₃Sn conductor, which facilitates quick energy extraction. This work presents the manufacturing of the copper-based coils, magnet assembly, and test results of the subscale SMCC2.