부산대학교 도서관

Undulators are X-ray sources which are widely used in synchrotron storage rings and free-electron laser (FEL) facilities. As the development of future light sources envisages smaller and more compact undulators, it is necessary to construct small-scale high-field undulators with short period lengths $\lambda \,< $ 10 mm and narrow magnetic gaps $d_\text{mag} < $ 4 mm. Therefore, high-temperature superconducting (HTS) tapes are a promising candidate, since they offer a high critical current density at higher temperatures. Instead of the commonly used wounded coils of low-temperature superconducting (LTS) wires, such as NbTi, to generate the alternating magnetic dipole field, a meandering pattern is structured on the surface of the HTS tape with ps laser pulses to provide a sinusoidal current path through the tape, see Fig. 1. This technique leads to a precise structure and at the same time prevents damage to the superconducting layer due to overheating. A new concept has been developed and improved at KIT. The new concept involves two opposing stacks of 30 laser-structured HTS tapes. The ends of each tape are soldered and connected to the tape above, resulting in an accordion-like arrangement, see Figs. 2 and 3. This paper presents the general design and the preparation of the stacks of the compact SCU, followed by the results of a Biot-Savart magnetic field simulation. The magnetic field measurement setup and a first current carrying test of the two coils are included.