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Design and construction of the undulators for the linac coherent light source (LCLS) at the Stanford Linear Accelerator Center (SLAC) is the responsibility of Argonne National Laboratory (ANL). A full-scale prototype undulator was constructed in-house and extensively tested at Argonne's advanced photon source (APS). The device was tunable to well within the LCLS requirements and was stable for five years. Experience constructing the prototype undulator led us to conclude that with appropriate engineering design and detailed assembly procedures, precision undulators can be constructed by highly-qualified industrial vendors without undulator-construction experience. Argonne's detailed technological knowledge and experience were transferred to the successful bidders who produced outstanding undulators. Our production concept for the 3.4-m-long, fixed-gap, planar-hybrid undulators with a 30-mm period is discussed. Manufacturing, quality assurance, and acceptance testing details are also presented.

Decreasing an ID vacuum chamber wall thickness is a way to achieve a smaller ID gap and a higher magnetic field without decreasing the clear beam aperture of the chamber. Multiple extruded aluminum ID vacuum chambers with 1-mm wall thickness were developed and fabricated at Argonne for the APS and several other synchrotron radiation facilities [1]. Thinner walls have been avoided due to fear that porosity and defects from the extrusion process would result in vacuum leaks. There were also concerns that thinner walls may have excessive deformation or may not withstand the stresses. Recently, several extrusions have been machined to a wall thickness of less than 1 mm to determine the practical limits. Using the extrusion for the insertion device vacuum chamber (ID VC) for the DESY FEL project with a 9.5-mm inner diameter and the LCLS test vacuum chamber extrusion, we decreased the wall thickness to 0.6, 0.5, and 0.4 mm to test the vacuum integrity for a thin wall in these extrusions. Structural analysis and test results are presented.

A precision positioning system has been designed for the Linac Coherent Light Source (LCLS) and a prototype system is being fabricated. The LCLS will use a beam-based alignment technique to precisely align all of the segments of the 131.52-m-long undulator line. The requirement for overlap between the electron beam and the x-ray beam, in order to develop and maintain lasing, demands that each quadrupole must be aligned within a tolerance of ± 7 μm and that undulator axes must be positioned within 5 μm vertically and 10 μm horizontally. Five cam movers, each with an eccentricity of 1.2 mm, will allow adjustment of a cradle supporting the undulator, its vacuum chamber, a quadrupole, and a beam position monitor. An additional motion transverse to the beam axis allows removal of individual undulators from the beam path. Positioning feedback will be provided by a wire position monitor system and a hydrostatic leveling system.

Six new types of insertion device vacuum chambers have been designed at the Advanced Photon Source (APS). One chamber has been designed for the APS canted undulator beamlines, two for the Canadian Light Source (CLS), and three for BESSY II. For the double canted undulators and CLS, a new extrusion shape with an oval aperture (not elliptical as usual) was developed and extruded. That required a thorough stress analysis and some compromise, which included a small increase of the vacuum chamber wall thickness. The details of the stress analyses and design of the chambers, along with lessons learned, are presented.

The vacuum requirement for the undulator line of the Linac Coherent Light Source is extremely challenging: a low resistive wall impedance 3.42-m-long chamber that fits within a 6.3 mm undulator gap that has ultralow outgassing and a surface finish, less than 100 nm Ra. A prototype chamber will be fabricated from electropolished semiconductor-processing-grade stainless-steel seamless tubing. Since stainless-steel tubing has a high electric resistivity, which can increase the resistive wall wake, a thin layer of copper will be deposited to minimize this effect. A thin nickel plating will be deposited in advance for better adhesion. This process will be followed by electropolishing of the copper surface. The first approach for Cu coating of the vacuum chamber has been investigated. Roughness measurements and preliminary coating results with a one-meter-long tube will be presented.

The Linac Coherent Light Source (LCLS) will require undulators with unprecedented mechanical precision in order to achieve the magnetic field requirements. Distortion of the undulator strongback due to the thermal effects and magnetic and gravitational forces could seriously degrade the performance. To minimize the distortion, a C-type, fixed-gap undulator with titanium strongback will be used. An analysis of the design of the structure and a comparison of the predicted results with the mechanical requirements and with magnetic measurements is presented.

During the last five years, a new approach to the design and fabrication of extruded aluminum vacuum chambers for insertion devices was developed at the Advanced Photon Source (APS). With this approach, three different versions of the vacuum chamber, with vertical apertures of 12 mm, 8 mm, and 5 mm, were manufactured and tested. Twenty chambers were installed in the storage ring and successfully integrated into the APS vacuum system. All have operated with beam, and 16 have been coupled with insertion devices. Two different vacuum chambers with vertical apertures of 16 mm and 11 mm were developed for the BESSY-II storage ring and 3 of the 16 mm chambers were manufactured.

The insertion devices (IDs) at the Advanced Photon Source have been magnetically tuned to minimize the integrals of the field through the devices and to minimize the variation of those integrals with gap, with a goal of not perturbing the stored particle beam. Measurements of the particle beam motion as the ID gap was changed found that the closed-orbit distortion was better than the requirement and agreed well with predictions based on magnetic measurement results. Another goal of the magnetic tuning is to ensure high brilliance in the low-order harmonics by keeping the rms phase error small.

The elliptical multipole wiggler (EMW) has been designed, constructed, and installed in the X13 straight section of the NSLS X-ray Ring. The EMW generates circularly polarized photons in the energy range of 0.1-10 keV with AC modulation of polarization helicity. The vertical magnetic field of 0.8 T is produced by a hybrid permanent magnet structure with a period of 16 cm. The horizontal magnetic field of 0.22 T is generated by an electromagnet, the core of which is fabricated from laminated iron to operate with a switching frequency up to 100 Hz. There are dynamic compensation trim magnets at the wiggler ends to control the first and second field integrals with very high accuracy throughout the AC cycle. The residual closed orbit motion due to the electromagnet AC operation is discussed.

A vacuum system for the insertion devices at the Advanced Photon Source was designed, and chambers of this design were successfully manufactured and tested. Three different versions of the vacuum chamber have been developed with vertical apertures of 12 mm, 8 mm, and 5 mm, respectively. The chambers are fabricated by extruding 6063 aluminum alloy to form a tube with the desired internal shape and machining the exterior to finish dimensions. The wall thickness of the completed chamber at the beam orbit position is 1 mm. The design utilizes a rigid strongback that limits deflection of the chamber under vacuum despite the thin wall. Chambers with lengths of 2.2 m and 5.2 m have been fabricated. Pumping is accomplished by a combination of lumped and distributed non-evaporable getters and ion pumps. An ultimate pressure of 5.1/spl times/10/sup -11/ torr was achieved with the 12-mm vertical aperture prototype. Alignment of the vacuum chamber on its support stand can be made with a precision of /spl plusmn/25 /spl mu/m in the vertical plane, which allows minimum insertion device pole gaps of 14.5 mm, 10.5 mm, and 7.5 mm.

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 /spl Aring/ 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.

Two insertion device magnetic structures have been prepared for the Advanced Photon Source (APS) FEL project. The magnetic structures are standard APS undulators, 2.4 m long with 3.3-cm period. Measurements and tuning of the undulators have been completed at a magnetic gap of about 9.3 mm, where K is 3.1. Special measurement and tuning techniques were used to satisfy the tight trajectory straightness requirement that the second field integral be less than 3.3 kG-cm/sup 2/. The magnetic field strengths of the undulators must be well matched; this leads to the requirement that the magnetic gap must be controlled to better than 10 microns. Proper phasing between the undulators is ensured by adjusting the length of the drift space between the undulators. The drift space length that is needed is strongly affected by the end fields of the magnetic structures. The results of measurements of the magnetic field and calculations of the drift length are provided.