NSLS-II Seminar

In the presentation we discuss feasibility of enhancement of the peak field in a short-period cryogenically-cooled hybrid permanent-magnet undualtor by using pole inserts with the saturation inductance Bsat over that of iron ( 2 - 2.5 Tesla). Magnetic simulations performed by RADIA magnetostatics code for the magnet material (PrFeB) and geometrical parameters of cryogenically-cooled permanent-magnet undulators considered for the development at the NSLS-II, demonstrate that the peak field continues to increase as Bsat of the pole is increased, reaching saturation at Bsat = 3.5 Tesla. Dysprosium metal, with the saturation inductance of 3.4 Tesla below 90 K, appears as a good candidate for the optimized pole material. However, due to high magnetic anisotropy of Dy, such a high level of magnetization can only be realized when the external field lies in the basal plane. This implies that the pole has to be single-crystalline or highly textured. Considering that the growing of large, >10 mm, Dy single crystals is difficult, we propose secondary re-crystallization as a method to induce the required texture in thin Dy foils. The textured foils can be stacked to produce pole inserts of the desired geometry and orientation. Results of small-scale processing and magnetic measurements of thin (20-60 microns) foils prove that the required texture quality can be achieved by relatively simple sequence of heat-treatment and rolling.