A Dual-Lunate-Ring Bulk RE-Ba-Cu-O Undulator

RE-Ba-Cu-O (REBCO) bulk high temperature superconducting undulators have been experimentally demonstrated to generate undulator fields exceeding 2 T at a 10 mm period, outperforming alternative undulator technologies for short-period applications. This study aims to further enhance undulator performance by reducing the period length through optimization of staggered-array, half-moon-shaped REBCO bulks. We propose a novel dual-lunate-ring-based REBCO undulator geometry that enables control of magnetization currents within individual lunate rings. The coexistence of magnetization currents on both the upper and lower sides of the undulator axis contributes to a significant enhancement of the on-axis magnetic field. To evaluate the performance of this design, the undulator period and gap were fixed at 7 mm and 3.3 mm, respectively, while the dimensions of the bulk rings were optimized numerically using the H-formulation. When the background solenoidal field changes from 10T to zero (ΔBs = 10 T), the undulator is expected to achieve a field strength B0 of 1.65T with a 7 mm period, corresponding to a deflection parameter of K = 1.1.