Sorting and Shimming Strategy for the HZB-In-Vacuum APPLE II IVUE32

Abstract The In-vacuum APPLE II IVUE32 at HZB will be the first undulator of this type. Due to RF-restrictions well-established shimming methods are difficult to adopt, and a precise characterization of magnet units in combination with an efficient sorting strategy is of utmost importance. The compensation of unavoidable systematic magnet inhomogeneities follows a similar strategy as for single magnet blocks of conventional BESSY II APPLE II. We present high accuracy stretched wire measurements of two recent HZB-in-air APPLE II devices, the UE48 (magnet pairs measured 2015) and the UE51 (magnet pairs measured 2020). These devices document the successful development of an efficient fabrication and sorting strategy including the compensation of magnet pair inhomogeneities, which has been done in collaboration with Vacuumschmelze. For the UE48 16 magnet pairs were re-magnetized (easy-axis reversal) for aiming at the targeted compensation level of inhomogeneities, whereas the UE51 magnet pairs encounter already a sufficient compensation level after fabrication. The suitability of the proven strategy for the IVUE32 will be discussed in the paper.