Development of Permanent Magnet Quadrupoles at NSRRC

Low emittance storage rings are the trend for the next generation of accelerators. The Taiwan Photon Source (TPS) is also planning to upgrade to this superior kind of storage ring in the future. The permanent magnet technology is key to the fabrication of such rings because it can be used to build very compact, large gradient, and energy-saving quadrupoles. We thus develop the relevant technologies for the projected future TPS upgrade and build quadrupoles for a compact X-ray Free Electron Laser. One quadrupole design has a hybrid type magnetic structure with a very small bore radius of 3.5 mm and very strong gradient of 330 T/m. The field is produced by permanent magnet blocks and pure iron yokes, which are fixed by non-magnetic mechanical parts. Although Nd ₂ Fe ₁₄ B has a higher field strength, it is more sensitive to temperature and is less radiation resistant than Sm ₂ Co ₁₇ is. Therefore, Sm ₂ Co ₁₇ was chosen to minimize the temperature effect and radiation damage. The gradient can be tuned by moving shunt plates, reaching a tunability of ± 15 T/m. A small thickness Hall probe was used to measure the central field gradient of the prototype device. The design and shape of the magnet pole, the fabrication process of a prototype and the field measurement results are presented in this article.