Modeling and Experimental Result of a Double Staggered-Array Helical Undulator Made of Stacked RE-Ba-Cu-O Tapes

High-temperature superconducting (HTS) materials have attracted significant interest for use in insertion devices due to their high critical temperature and larger critical current density. These properties enable the development of undulators with short period and large on-axis magnetic field. To facilitate the future upgrade of the Shanghai Soft X-ray Free Electron Laser (SXFEL) facility, we propose the development of a 12 mmperiod HTS helical undulator incorporating a double staggeredarray of stacked RE-Ba-Cu-O tapes, supplied by Shanghai Creative Superconductor. Numerical optimization of various stacked tape configurations indicates that an on-axis dual sinusoidal magnetic field, with a 90° phase shift between the Bx and By components and equal amplitudes of 0.57 T, can be achieved with a magnetic gap of 6 mm at 20 K. At 4.2 K, the attainable field amplitude increases to B<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x0</sub> = B<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y0</sub> = 0.70 T. This study presents the details of the numerical calculations, fabrication of the stacked tape assemblies, preparation of the undulator prototype, and preliminary results from field-cooled magnetization tests and surface magnetic field mapping conducted at 77 K.