HALL PROBE MEASUREMENTS OF 80 UNIT CELL MAGNETS FOR THE MAX-IV STORAGE RING A

80 unit cell magnet segments have been manufactured by Scanditronix Magnet for the 3 GeV storage ring at MAX-IV in Lund, Sweden. All of the magnets have been approved by Max-lab after a large field measuring campaign using both a high precision Hall probe bench, as well as a new rotating coil system. Each unit cell magnet consists of one dipole, two quadrupole, three sextupole and one vertical and one horizontal corrector magnets. The Hall probe bench was used to measure the dipole magnet (with combined dipole and quadrupole component) as well as the quadrupole magnets. This paper will focus on the Hall probe measurements performed on the dipole magnets from the perspective of a manufacturer. E.g. the repeatability of the measurements and the relation between field performance and mechanical tolerances will be analysed. MAX-IV MAX-IV aims to be the new centre for synchrotron light in Sweden, and will be the replacement of the smaller MAX-II and MAX-III storage rings. The accelerator complex will consist of a linac and two storage rings (see Fig. 1), with the larger one having a circumference of 528 m and electron energy of 3 GeV. The concept is similar to that of the MAX-III accelerator, focusing on a compact magnet design, with combined function magnets. Also with separate magnetic elements built into the same iron block. This keeps the overall dimensions of the magnets down, as well as simplifies the alignment of the magnets [1]. The entire 3 GeV storage ring contains 20 achromats, with each achromat consisting of two matching cells and five unit cells. The cells contain one dipole magnet each which gives the storage ring the advantages of a multibend achromat lattice, which lowers the electron beam emittance. It also has the benefits of increasing the energy acceptance, as well as improves the dynamic aperture [2]. Figure 1: An overview of the MAX-IV accelerator complex. Courtesy of MAX IV Laboratory. Scanditronix has produced four of the five unit cell families (U1, U2, U4 and U5) as seen in Fig. 2. The magnets contained in the U1 and U5 cells are identical, and U2 and U4 as well, the only difference is that the cells are mirrored versions of each other. However, all four families contain the same dipole magnet. Figure 2: Image of one achromat (mock-up). Courtesy of MAX IV Laboratory. Scanditronix Magnet selected two subcontractors for the machining of the iron blocks to keep the tight time schedule for the project. One company produced the U1 and U2 segments, and the other produced the U4 and U5 segments. It is seen from the results of the field measurements that there are no significant difference between the magnets machined at the two subcontractors. HALL PROBE BENCH Scanditronix Magnet acquired a new state-of-the-art Hall probe mapping bench (see Fig. 3) to meet the high precision in measurements that was required by Max-lab. This is located in a temperature controlled room where the magnets were stored until correct measuring temperature was achieved. The base of the measurement system is a 3D coordinate measuring machine (CMM) of portal type from Hexagon Metrology. This is built on a flat table of solid granite, to ensure a horizontal placement of the magnets, as well as a good resistance against vibrations. The CMM has been equipped with a Hall probe and teslameter from Group3, with an absolute accuracy of ±0.01% of reading ±0.006% of range [3]. The CMM has a volumetric measuring range of 3000x1200x1000 mm, and an accuracy of about 5 m per 6th International Particle Accelerator Conference IPAC2015, Richmond, VA, USA JACoW Publishing ISBN: 978-3-95450-168-7 doi:10.18429/JACoW-IPAC2015-WEPMN066 WEPMN066 3076 Co nt en tf ro m th is w or k m ay be us ed un de rt he te rm so ft he CC BY 3. 0 lic en ce (© 20 15 ). A ny di str ib ut io n of th is w or k m us tm ai nt ai n at tri bu tio n to th e au th or (s ), tit le of th e w or k, pu bl ish er ,a nd D O I. 7: Accelerator Technology T09 Room Temperature Magnets meter, which makes it very suitable for the measurements of the over 2.4 m long magnet block. Figure 3: The Hall probe mapping bench. After machining of the iron the five fiducial spheres on the yoke top surface were measured by the subcontractor in the coordinate system of the magnet block. Prior to the field mapping, the fiducial spheres where measured with the mechanical probe of the Hall probe bench, which then performed a standard best fit algorithm to align itself to the magnet block. This made it possible to measure the field using the same fiducials that are then used for the actual installation of the magnet in the storage ring. The original idea was to measure directly on the fiducial surfaces located on the sides of the iron block, which were used as reference for the machining and the measurement of the spheres at the sub-contractor. However, this would have introduced another source for error when comparing the coordinate system used for the field measurements to the actual alignment of the block in the storage ring.