Performance of the Full-Length Vertical Polarizing Undulator Prototype for LCLS-II

As part of the LCLS-II R&D program, a novel 3.4-meter long undulator prototype with horizontal main magnetic field and dynamic force compensation - called the horizontal gap vertical polarization undulator (HGVPU) - has recently been developed at the Advanced Photon Source (APS). Initial steps of the project included designing, building, and a testing 0.8-meter long prototype. Extensive mechanical testing of the HGVPU has been carried out. The magnetic tuning was accomplished by applying a set of magnetic shims. As a result, the performance of the HGVPU meets all the stringent requirements for the LCLS-II insertion device, which includes limits on the field integrals and phase errors for all operational gaps, as well as the reproducibility and accuracy of the gap settings. The HGVPU has been included in the baseline of the LCLS-II project for the hard x-ray undulator line.