• G. Rakowsky
  BNL, Upton, Long Island, New York

Various magnet sorting strategies have been used to minimize trajectory and phase errors in undulators, ranging from intuitive pairing of stronger and weaker magnets, to full 3D FEM simulation with actual Helmholtz coil magnet data. We present a simpler approach, first deriving trajectory displacement, kick angle and phase error signatures of each component of magnetization error from a 3D Radia* undulator model. Then, for a given sequence of magnets, the trajectory and phase profiles are computed by cumulatively summing the scaled displacements and phase errors. The rms error is then minimized by swapping magnets according to one's favorite optimization method. A fast, simple magnet swapping algorithm, implemented in Mathematica, is described. 100,000 iterations take only minutes, so dozens of solutions can be compared. This approach was applied recently at NSLS to a short in-vacuum undulator, which required no trajectory or phase shimming. We also obtain trajectory and phase error signatures of some mechanical errors, to guide "virtual shimming" and specifying mechanical tolerances. Finally, multipole signatures of some simple inhomogeneities are modeled.

* O. Chubar, P. Elleaume, J. Chavanne, "A 3D Magnetostatics Computer Code for Insertion Devices", SRI97 Conference August 1997, J. Synchrotron Rad. (1998). 5, 481-484

• T. Tanabe, O.V. Chubar, T.M. Corwin, D.A. Harder, P. He, G. Rakowsky, J. Rank, C.J. Spataro
  BNL, Upton, Long Island, New York

National Synchrotron Light Source-II (NSLS-II) project is now in the construction stage. A new insertion device (ID) magnetic measurement facility (MMF) is being set up at Brookhaven National Laboratory in order to satisfy the stringent requirement on the magnetic field measurement of IDs. ISO-Class7 temperature stabilized clean room is being constructed for this purpose. A state-of-the-art Hall probe bench and integrated field measurement system will be installed therein. IDs in the project baseline scope include six damping wigglers, two elliptically polarizing undulators (EPUs), three 3.0m long in-vacuum undulators (IVUs) and one 1.5m long IVU. Three-pole wigglers with peak field over 1 Tesla will be utilized to accommodate the users of bending magnet radiation at the NSLS. Future plan includes: 1) an in-vacuum magnetic measurement system, 2) use of PrFeB magnet for improved cryo undulator, 3) development of advanced optimization program for sorting and shimming of IDs, 4) development of a closed loop He gas refrigerator, 5) switchable quasi-periodic EPU. Design features of the baseline devices, IDMMF and the future plans for NSLS-II ID activities are described.