Design and manufacture of a prototype undulator for the LCLS project

The goal of the Linac Coherent Light Source (LCLS) project is to build a free-electron laser (FEL) that will produce X-rays of 1.5 Å wavelength by sending a 14.35 GeV electron beam from the Stanford Linear Accelerator through a line of undulators. The undulator line will consist of a series of 3.4-m-long undulator sections, with diagnostics inserted between the sections. The design for an undulator section has been completed, and a prototype is under construction at the Advanced Photon Source. The undulator will be a fixed-gap device, with a magnetic pole gap of 6 mm and a period of 30 mm. The strongback is machined with high accuracy from a solid, forged Ti bar. Titanium was chosen for its low thermal expansion and for its strength and low density, which will reduce the weight and the deflection of the strongback under gravity. Stringent magnetic requirements demand a stable undulator, and the fixed gap will help achieve it