The ESRF Insertion Devices

The European Synchrotron Radiation facility is presently operating 47 segments of insertion devices (IDs). A record brilliance of 1 × 10²⁰ photons s^-1 (0.1% bandwidth)^-1 mm^-2 mrad^-2 has been reached. Almost all devices are built with permanent magnets with or without iron pole pieces. They have been mechanically and magnetically designed and field-measured in house. Multipole shimming has been applied to all devices to remove the integrated dipole and higher-order multipole fields, thereby reducing the interaction between the IDs and the stored beam. For all undulators, the field errors have been corrected further using spectrum shimming in order to achieve ideal spectral brilliance on all harmonic numbers from 1 to 15. A significant effort has been made to optimize the magnet terminations for both field-integral correction and phasing. A phasing scheme of the undulator segments has been developed which allows the independent manufacture and operation of individual segments. Several designs for undulator phasing are presented, together with a comparison between hybrid and pure-permanent-magnet technology. A new type of variable-polarization helical undulator is presented.