Mechanical design of the VISA undulator

As part of the research and development effort for a 4th generation light source, we have designed a 4-meter long free-electron laser (FEL) undulator. The undulator will be installed at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory to conduct a self-amplified spontaneous emission (SASE) demonstration. The demonstration is called VISA, which stands for "Visible to Infrared SASE Amplifier." The undulator consists of 440 permanent dipole magnets per meter which are supported and aligned on a precision strongback. Focusing and defocusing permanent quadrupole magnets are also supported by the strongback. Each of the 4 one-meter sections of undulator are kinematically supported and housed within the vacuum vessel. The undulator and the vacuum vessel are supported independently to eliminate undulator misalignment during vacuum pump-down of the vessel. We describe the design requirements and features of the undulator, vacuum vessel and support system.