Field uniformity enhancement in a prototype high-temperature superconducting dipole magnet

Area of Science:

• Superconducting Magnet Technology
• Particle Accelerator Physics
• Materials Science

Background:

• High-temperature superconducting (HTS) magnets are crucial for MRI, NMR, fusion, and particle accelerators requiring higher magnetic fields.
• Saddle geometry dipole magnets are needed for synchrotrons, with REBCO emerging as a promising HTS material.
• Ensuring spatial homogeneity and temporal stability of the magnetic field is critical for beam lines.

Purpose of the Study:

• To demonstrate improved field uniformity in a conduction-cooled, no-insulation (NI) REBCO saddle dipole magnet.
• To assess strategies for mitigating magnetic field non-uniformity caused by screening-current-induced field (SCIF) and fabrication errors.
• To provide a practical route towards achieving low-temperature-superconducting (LTS)-class field uniformity in compact, cryogen-free HTS dipole magnets.

Main Methods:

• Engineered a conduction-cooled, no-insulation (NI) REBCO saddle dipole magnet with a 0.5 T central field.
• Assessed current sweep reversal (CSR) and passive shimming with AISI 1008 ferroshim to improve magnetic field uniformity.
• Utilized numerical simulations and experimental validations to analyze the impact of each technique.

Main Results:

• CSR improved spatial uniformity by approximately 0.4×.
• Passive shimming with ferroshim enhanced uniformity by 4.5×.
• Achieved sextupole-dominant harmonics with small skew residuals and temporal drift ≤0.38× [Formula: see text] [Formula: see text].

Conclusions:

• Both CSR and passive shimming effectively mitigate magnetic field non-uniformity in REBCO dipole magnets.
• Passive shimming offers a significantly greater improvement in field uniformity compared to CSR.
• The study presents a viable method for achieving LTS-class field uniformity in NI HTS dipole magnets.