Search

A preliminary design of the multi-meter long collinear dielectric wakefield accelerator that achieves a highly efficient transfer of the drive bunch energy to the wakefields and to the witness bunch is considered. It is made from ~0.5 m long accelerator modules containing a vacuum chamber with dielectric-lined walls, a quadrupole wiggler, an rf coupler, and BPM assembly. The single bunch breakup instability is a major limiting factor for accelerator efficiency, and the BNS damping is applied to obtain the stable multi-meter long propagation of a drive bunch. Numerical simulations using a 6D particle tracking computer code are performed and tolerances to various errors are defined.

A 0.27 meV-bandwidth monochromator for 21.5 keV synchrotron radiation demonstrates exceptional stability using cryogenic stabilization and active feedback control., A high-resolution silicon monochromator suitable for 21.541 keV synchrotron radiation is presented that produces a bandwidth of 0.27 meV. The operating energy corresponds to a nuclear transition in 151Eu. The first-of-its-kind, fully cryogenic design achieves an energy-alignment stability of 0.017 meV r.m.s. per day, or a 100-fold improvement over other meV-monochromators, and can tolerate higher X-ray power loads than room-temperature designs of comparable resolution. This offers the potential for significantly more accurate measurements of lattice excitation energies using nuclear resonant vibrational spectroscopy if combined with accurate energy calibration using, for example, high-speed Doppler shifting. The design of the monochromator along with its performance and impact on transmitted beam properties are presented.

Development of superconducting undulators continues at the Advanced Photon Source (APS). Two years after successful installation and commissioning of the first relatively short superconducting undulator ``SCU0'' in Sector 6 of the APS storage ring, the second 1.1-m-long superconducting undulator ``SCU1'' was installed in Sector 1 of the APS. The device has been in user operation since its commissioning in May 2015. This paper describes the magnetic and cryogenic design of the SCU1 together with the results of stand-alone cold tests. The SCU1's magnetic and cryogenic performance as well as its operating experience in the APS storage ring are also presented.

As part of the R&D program of the LCLS-II project, a novel 3.4-meter-long undulator prototype with horizontal magnetic field and dynamic force compensation has recently been developed at the Advanced Photon Source (APS). Previous steps in this development were the shorter 0.8-meter-long and 2.8-meter-long prototypes. Extensive mechanical and magnetic testing were carried out for each prototype, and each prototype was magnetically tuned using magnetic shims. The resulting performance of the 3.4-meter-long undulator prototype meets all requirements for the LCLS-II insertion device, including limits on the field integrals, phase errors, higher-order magnetic moments, and electron-beam trajectory for all operational gaps, as well as the reproducibility and accuracy of the gap settings.

We report progress on implementation and commissioning of sequential X-ray diffraction topography at 1-BM Optics Testing Beamline of the Advanced Photon Source to accommodate growing needs of strain characterization in diffractive crystal optics and other semiconductor single crystals. The setup enables evaluation of strain in single crystals in the nearly-nondispersive double-crystal geometry. Si asymmetric collimator crystals of different crystallographic orientations were designed, fabricated and characterized using in-house capabilities. Imaging the exit beam using digital area detectors permits rapid sequential acquisition of X-ray topographs at different angular positions on the rocking curve of a crystal under investigation. Results on sensitivity and spatial resolution are reported based on experiments with high-quality Si and diamond crystals. The new setup complements laboratory-based X-ray topography capabilities of the Optics group at the Advanced Photon Source.

Projection X-ray topography of single crystals is a classic technique for the evaluation of intrinsic crystal quality of large crystals. In this technique a crystal sample and an area detector (e.g., X-ray film) collecting intensity of a chosen crystallographic reflection are translated simultaneously across an X-ray beam collimated in the diffraction scattering plane (e.g., [1, 2]). A bending magnet beamline of a third-generation synchrotron source delivering x-ray beam with a large horizontal divergence, and therefore, a large horizontal beam size at a crystal sample position offers an opportunity to obtain X-ray topographs of large crystalline samples (e.g., 6-inch wafers) in just a few exposures. Here we report projection X-ray topography system implemented recently at 1-BM beamline of the Advanced Photon Source. A selected X-ray topograph of a 6-inch wafer of 4H-SiC illustrates capabilities and limitations of the technique.

Lasing in a hard-X-ray free-electron laser is typically seeded from noise due to the self-amplification of spontaneous emission, which limits temporal coherence and spectral characteristics. Researchers now demonstrate self-seeding using X-rays from the first half of the magnetic undulator to seed the second half via a diamond-based monochromator at angstrom wavelengths.

A superconducting planar undulator is under development at the Advanced Photon Source. The R&D phase culminated in the successful testing of several short magnetic structure prototypes. Work is now focused on a complete design for the first undulator. The conceptual designs for its superconducting magnet, the cooling system, and the cryostat are described in this paper.

Computer simulations using a continuous change in particle energy are an important tool in improving the performance at the final stage of the Linac Coherent Light Source (LCLS) undulator line. Changes in the particle energy cause the break length between undulator segments to no longer be optimized. Radiation losses less than 0.1%/undulator segment can be easily compensated by adjustment of an undulator deflection parameter K. For higher losses, up to 0.4%, adjustment of K can still be compensated, but careful optimization is required. Compensating for losses greater than 0.4% requires tapering of the field within the undulator segment. The LCLS undulator segments are in mass production at this time. The first two undulators for the LCLS project were delivered to the APS magnetic measurement facility. They have already been tuned, and meet all requirements for the LCLS free-electron laser (FEL). The final results of this tuning will be presented, with emphasis on the FEL-specific requirements. A systematic zero shift in the Sentron [ 〈http://www.sentron.ch/〉 . [1] ] 2-axis Hall probe was discovered, which required correction in order to obtain the proper field integrals.

The design of a new hybrid-type undulator with a fixed gap of 6.4 mm, a period of 30 mm and a length of 3.4 m is presented. The fractional variations in deflection parameter K between segments of 130.4-m-long undulator line for the Linac Coherent Light Source (LCLS) must be ⩽1.5×10−4. Major design features and their choices are discussed. Lessons learned while working with this prototype are critical for successful project execution. Although the prototype undulator met all of the LCLS specifications, development continued in order to simplify the system. A canted-pole geometry was adopted, which allows the K value to be changed by lateral translation of the entire undulator segment. The prototype undulator was subsequently modified to test the canted-pole concept. Magnetic measurements demonstrated that the undulator with canted poles meets all LCLS specifications and is more cost effective to implement.

A full-length 30-mm-period prototype undulator segment has been constructed for the Linac Coherent Light Source (LCLS) project. It is a 3.42-m-long planar permanent magnet hybrid device with a fixed gap near 6.35 mm. The magnetic structure was assembled from a set of 500 magnets that were purchased from Shin-Etsu. A subset of the magnets was measured in a Helmholtz coil system to check the accuracy of the vendor's measurements of the magnetic moments. A specially designed half-period fixture was used for Hall probe measurements of the magnetic field of all the magnet blocks. The magnets were sorted based on the vendor's data of the total magnetic moment and our measurements of the field integrals. The trajectory calculated from Hall probe measurements of the assembled device was within the specified tolerance (deviation

Currently, a Linac Coherent Light Source (LCLS) prototype undulator is under construction. The prototype is a 3.4-m-long hybrid-type undulator with fixed gap of 6 mm. The period length is 30 mm and the number of poles is 226. For this undulator, 450 NdFeB magnet blocks are used. This project does not have demanding requirements for multipole component errors, but the field strength at x =0 should be as precise as possible to provide proper particle steering and phase errors. The first set of magnetic blocks has been measured. The strength and direction of magnetization of the magnet blocks are measured using a Helmholtz coil system. In addition to this, Hall probe measurements are performed for magnet blocks while they are mounted in a specially designed cassette with vanadium-permendur poles. The magnet blocks will be sorted using these data to minimize errors. Computer simulations show that magnets may be sorted in decreasing strengths with little or no additional tuning of the undulators.

The Advanced Photon Source self-amplified spontaneous emission (SASE) free-electron laser (FEL) uses diagnostics between undulator sections to characterize the light and the electron beam. These diagnostics enable z-dependent measurements of the exponential growth of the radiation and of the microbunching. The original diagnostics were designed for visible light. To enable measurements down to 265 nm, UV-enhanced cameras and fused-silica lenses have been installed. We have now designed a diagnostics suite that will enable us to continue measurements down to 50 nm using reflective optics and back-illuminated CCD cameras operating in vacuum. We describe the enhancements to the diagnostics for operation in the UV and VUV.

A short prototype (847-mm-long) of an Insertion Device (ID) with the dynamic compensation of ID magnetic forces has been designed, built, and tested at the Advanced Photon Source (APS) of the Argonne National Laboratory. The ID magnetic forces were compensated by the set of conical springs placed along the ID strongback. Well-controlled exponential characteristics of conical springs permitted a very close fit to the ID magnetic forces. Several effects related to the imperfections of actual springs, their mounting and tuning, and how these factors affect the prototype performance has been studied. Finally, series of tests to determine the accuracy and reproducibility of the ID magnetic gap settings have been carried out. Based on the magnetic measurements of the ID Beff, it has been demonstrated that the magnetic gaps within an operating range were controlled accurately and reproducibly within ±1 μm. Successful tests of this ID prototype led to the design of a 3-m long device based on the same concept. The 3-m long prototype is currently under construction. It represents R&D efforts by the APS toward APS Upgrade Project goals as well as the future generation of IDs for the Linac Coherent Light Source (LCLS).

Exponential growth of self-amplified spontaneous emission at 530 nm was first experimentally observed at the Advanced Photon Source low-energy undulator test line in December 1999. Since then, further detailed measurements and analysis of the results have been made. Here, we present the measurements and compare these with calculations based on measured electron beam properties and theoretical expectations.

Self-amplified spontaneous emission in a free-electron laser has been proposed for the generation of very high brightness coherent x-rays. This process involves passing a high-energy, high-charge, short-pulse, low-energy-spread, and low-emittance electron beam through the periodic magnetic field of a long series of high-quality undulator magnets. The radiation produced grows exponentially in intensity until it reaches a saturation point. We report on the demonstration of self-amplified spontaneous emission gain, exponential growth, and saturation at visible (530 nanometers) and ultraviolet (385 nanometers) wavelengths. Good agreement between theory and simulation indicates that scaling to much shorter wavelengths may be possible. These results confirm the physics behind the self-amplified spontaneous emission process and forward the development of an operational x-ray free-electron laser.

Three vacuum chambers for the VUV SASE FEL undulator sections at the TESLA Test Facility (TTF) were designed, built, tested and installed. Each chamber is 4.5 m long and of 11.5 mm thick. The inner diameter of the beam pipe is 9.5 mm. The rectangular chamber pro"le with a width of 128 mm is used to integrate beam position monitors and steerers. This is needed to provide a good overlap between the electron and the photon beam over the entire undulator length. The chambers are built in an aluminum extrusion technology developed for the insertion device vacuum chambers of the Advanced Photon Source. After manufacturing, special processing was performed to reach low outgassing rates ((1]10~11mbar) l/s) cm2) and particle-free chambers. Mounting of the chambers at TTF were performed under clean room conditions better class 100. ( 2000 Elsevier Science B.V. All rights reserved.

A self-amplified spontaneously emitting (SASE) free-electron laser (FEL) for the visible-to-ultraviolet spectral range is under construction at the Advanced Photon Source at Argonne National Laboratory. The amplifier part of the FEL consists of twelve identical 2.7-m-long sections. Each section includes a 2.4-m-long, 33-mm-period hybrid undulator, a quadrupole lens, and a set of electron beam and radiation diagnostics equipment. The undulators will operate at a fixed magnetic gap (approx. 9.3 mm) with K=3.1. The electron beam position will be monitored using capacitive beam position monitors, YAG scintillators with imaging optics, and secondary emission detectors. The spatial distribution of the photon beam will be monitored by position sensitive detectors equipped with narrow-band filters. A high-resolution spectrograph will be used to observe the spectral distribution of the FEL radiation.

A Low-Energy Undulator Test Line (LEUTL) is under construction at the Advanced Photon Source (APS). Its purpose is to fully characterize innovative, future-generation undulators, and to act as a test line in pursuit of generating coherent radiation at wavelengths down to a few tens of nanometers. The line will use a high-brightness RF electron gun as its source and the APS linac to accelerate these electrons up to >650 MeV. This beam will then be directed through undulators located in a new 50 m long enclosure. In addition, there is an end station external to the radiation environment which will house the equipment necessary to directly study the light generated by the beam and undulator system. At present, the new enclosures are complete, the electron rf gun is installed and operational, and a part of the necessary transport line is installed. A prototypical undulator cell, suitable for testing the requirements of single-pass free-electron laser operation, is near completion and will be installed during the winter shutdown of 1998. This paper will describe the LEUTL project and, in particular, its capabilities for exploring the self-amplified spontaneous emission process.

We present a pulsed-magnet system that enables x-ray single-crystal diffraction in addition to powder and spectroscopic studies with the magnetic field applied on or close to the scattering plane. The apparatus consists of a single large-bore solenoid, cooled by liquid nitrogen. A second independent closed-cycle cryostat is used for cooling samples near liquid helium temperatures. Pulsed magnetic fields close to $\sim 30$ T with a zero-to-peak-field rise time of $\sim$2.9 ms are generated by discharging a 40 kJ capacitor bank into the magnet coil. The unique characteristic of this instrument is the preservation of maximum scattering angle ($\sim 23.6^\circ$) on the entrance and exit sides of the magnet bore by virtue of a novel double-funnel insert. This instrument will facilitate x-ray diffraction and spectroscopic studies that are impractical, if not impossible, to perform using split-pair and narrow-opening solenoid magnets, and offers a practical solution for preserving optical access in future higher-field pulsed magnets., Comment: Accepted for publication in Rev. Sci. Instrum

The engineering of a dual-cryostat for a pulsed-magnet instrument at the Advanced Photon Source is presented. The dual-cryostat independently cools the magnet coil (using liquid-nitrogen) and the sample (using a closed-cycle refrigerator). Liquid-nitrogen cooling may allow a repetition rate of a few minutes for peak fields near 30 T. The system is unique in that the liquid-nitrogen cryostat incorporates a double-funnel vacuum tube passing through the solenoid's bore in order to preserve the entire angular range allowed by the magnet bore for scattering studies. Second, the use of a separate refrigerator for the sample allows precise positioning of samples in the bore while minimizing magnet vibrations propagating to the sample during pulsed-field generation.

A superconducting planar undulator with 9.5 mm pole gap, 16 mm period and required peak field 0.64 T is at present under development at the Advanced Photon Source. Magnet structure precision is a key component of the project. The current design of the magnet structure is based on the assembled jaws with individual poles, while previous designs utilized solid cores with machined coil grooves. Each jaw has a core with pole grooves and separate precise poles inserted in these grooves and fixed with small screws. This approach allows achieving a uniformity of the poles thickness to within 15 µm, improving the surface finish, as well as using magnetic poles with non-magnetic cores. Several 42-pole jaws have already been produced, wound and tested. Magnetic measurements of the first structure have confirmed the mechanical precision of the assemblies. Details of the magnet structure design and jaw assembly, and changes made from the first prototype system to the production unit, are presented here.

In the present work the SR beam lines at the TNK are described. Two types of SR beam lines are considered: for radiation from strong-field superconducting wigglers in the 0.2–5 A wavelength range and for radiation from bending magnets, undulators and multipole wigglers in the 5–2000 A range.

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 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.

At the Advanced Photon Source, three new beamlines will use an undulator configuration enabling the simultaneous use of two photon beams from a single straight section. To accommodate this configuration, a new front end was designed that is capable of handling the power of two undulators, with a beam separation of 1 mrad and a stored beam current of 200 mA at 7 GeV. Commissioning of the first front end took place early this summer. The design and major benefits of the new front‐end components will be discussed in this paper.

The use of circularly polarized radiation is advantageous for the study of magnetic materials using x‐ray scattering techniques. The APS is an ideal source of x‐ray radiation for such studies. We present a description of the elliptical multipole wiggler (EMW) [S. Yamamoto, H. Kawata, H. Kitamura, and M. Ando, Phys. Rev. Lett. 62, 2672 (1989)] to be constructed at the APS. This device has been chosen for reasons of tunability and special polarization properties. This insertion device is capable of producing circularly polarized x rays on axis. The EMW period will be λu=16 cm, the number of full strength poles in the hybrid structure is 31, and the device length is 2.8 m. The hybrid magnetic structure produces a peak vertical magnetic field with Ky=14 and the electromagnet provides horizontal magnetic field with Kx=1–2. The frequency of the horizontal field change is up to 10 Hz. The beamline will consist of three stations operating in tandem with only one station receiving x rays at any one time. The three...

The Stanford Linear Accelerator Center, in collaboration with Argonne National Laboratory, Brookhaven National Laboratory, Los Alamos National Laboratory, Lawrence Livermore National Laboratory, and the University of California at Los Angeles, have collaborated to create a conceptual design for a Free-Electron-Laser (FEL) R&D facility operating in the wavelength range 1.5-15 {angstrom}. This FEL, called the ''Linac Coherent Light Source'' (LCLS), utilizes the SLAC linac and produces sub-picosecond pulses of short wavelength x-rays with very high peak brightness and full transverse coherence. The first two-thirds of the SLAC linac are used for injection into the PEP-II storage rings. The last one-third will be converted to a source of electrons for the LCLS. The electrons will be transported to the SLAC Final Focus Test Beam (FFTB) Facility, which will be extended to house a 122-m undulator system. In passing through the undulators, the electrons will be bunched by the force of their own synchrotron radiation to produce an intense, spatially coherent beam of x-rays, tunable in energy from 0.8 keV to 8 keV. The LCLS will include two experiment halls as well as x-ray optics and infrastructure necessary to make use of this x-ray beam for research in a variety of disciplines suchmore » as atomic physics, materials science, plasma physics and biosciences. This Conceptual Design Report, the authors believe, confirms the feasibility of constructing an x-ray FEL based on the SLAC linac.« less

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.

We use Fresnel zone plates as focusing optics in hard x-ray microprobes at energies typically between 6 and 30 keV. While a spatial resolution close to 0.1 {micro}m can currently be achieved, highest spatial resolution is obtained only at reduced diffraction efficiency due to manufacturing limitations with respect to the aspect ratios of zone plates. To increase the effective thickness of zone plates, we are stacking several identical zone plates on-axis in close proximity. If the zone plates are aligned laterally to within better than an outermost zone width and longitudinally within the optical near-field, they form a single optical element of larger effective thickness and improved efficiency and reduced background from undiffracted radiation. This allows us both to use zone plates of moderate outermost zone width at energies of 30 keV and above, as well as to increase the efficiency of zone plates with small outermost zone widths particularly for the energy range of 6-15 keV.

There are 236 vacuum chambers and 23 special insertion device vacuum chambers installed at the Advanced Photon Source storage ring. Each is fabricated from an aluminum extrusion, followed by machining and welding. The standard vacuum chambers have a vertical aperture of 42 mm with a synchrotron radiation extraction channel of 10 mm, while 21 of the insertion device chambers have an 8 mm vertical aperture with an outside dimension of 10 mm, and two insertion device chambers have a 5 min vertical aperture with an outside dimension of 8 mm. The minimum pole gap in the insertion devices is 10.5 mm and 8.5 mm, respectively. The standard vacuum chambers are installed and aligned to /spl plusmn/150 microns, while the insertion device chambers are aligned to /spl plusmn/75 microns. All chambers have distributed NEG strip pumping, with ion pumps and lumped NEG pumps at locations of high gas loads, such as absorbers. During construction, all vacuum chambers were certified for use at 2/spl times/10/sup -10/ Torr. During operation, vacuum with 100 mA beam current is about 3/spl times/10/sup -10/ Torr. Without the beam, the vacuum is in the 10/sup -11/ Torr range. Both chamber types incorporate an antechamber design. The so-called "NEG dust" effect has not been observed. We have over five years of commissioning and operations experience at the APS, without any sign of aging of all the major components. Important design features and operations experience are discussed.

We present the first observation of Self-Amplified Spontaneous Emission (SASE) in a free-electron laser (FEL) in the Vacuum Ultraviolet regime at 109 nm wavelength (11 eV). The observed free-electron laser gain (approx. 3000) and the radiation characteristics, such as dependency on bunch charge, angular distribution, spectral width and intensity fluctuations all corroborate the existing models for SASE FELs., 6 pages including 6 figures; e-mail: joerg.rossbach@desy.de

Linearly and circularly polarized x-rays have been very successfully applied to the study of the properties of materials. Many applications can benefit from the availability of energy-tunable, high-brilliance x-ray beams with adjustable polarization properties. A helical undulator that can generate beams of variable (linear to circular) polarization has been designed and built by the Budker Institute of Nuclear Physics and the Advanced Photon Source. The first harmonic of this 12.8-cm-period device will cover the energy range from 0.4 keV to 3.5 keV. An important feature of this fully electromagnetic device is that it will allow us to generate 100% horizontally (Kx=0) or vertically (Ky=0) plane-polarized radiation, which will enable many experiments otherwise not technically feasible. With symmetric deflection parameters (Kx=Ky), the on-axis radiation will be circularly polarized, with a user-selectable handedness. The polarization can be changed at rates up to 10 Hz.

We have developed a x-ray microprobe in the energy region from 6 to 20 keV using undulator radiation and zone-plate optics for microfocusing-based techniques and applications at a beamline at the Advanced Photon Source (APS). The performance of the beamline was shown to meet our design objectives, including preservation of the source brilliance and coherence, selectable transverse coherence length and energy bandwidth, high angular stability, and harmonic suppression of the beam. These objectives were achieved by careful thermal management and use of a novel mirror and crystal monochromator cooling geometry. All beamline optical components are water cooled, and the x-ray beam in the experiment station is stable in beam intensity, energy, and position over many days with no active feedback. Using a double-crystal Si(111) monochromator, we have obtained a focal spot size (FWHM) of 0.15 μm(v)×1.0 μm(h), and a photon flux of 4×109 photons/sec at the focal spot, and thus a photon flux density gain of 15,000. A...

A design of a special synchrotron radiation absorber for the storage ring VEPP-4M is presented. The density of the synchrotron radiation power on the absorber surface is up to 500 W/mm 2 . The absorber is made from a beryllium plate, brazed inside to the copper vacuum chamber, which is intensively water-cooled from outside.

Construction of a single-pass free-electron laser (EEL) based on the self-amplified spontaneous emission(SASE) mode of operation is nearing completion at the Advanced Photon Source (APS) with initialexperiments imminent. The APS SASE FEL is a proof-of-principle fourth-generation light source. As of January 1999 the undulator hall, end-station building, necessary transfer lines, electron and opticaldiagnostics, injectors, and initial undulators have been constructed and, with the exception of the undulators, installed. All preliminary code development and simulations have also been completed. Theundulator hall is now ready to accept first beam for characterization of the output radiation. It is the project goal to push towards full EEL saturation, initially in the visible, but ultimately to UV and VUV, wavelengths.Keywords: Advanced Photon Source, APS, free-electron laser, FEL, self-amplified spontaneous emission,SASE, injector, linac, undulator, diagnostics 1. INTRODUCTION Synchrotron light sources are presently in their third generation, where a generation can loosely be definedby the available source brightness. The accelerator community has been developing ideas to push beyondthe present third generation and so usher in the next or fourth generation of light sources together with thescientific explorations pursued with these sources. However, until recently there was no clear consensus on

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.

We have constructed a high resolution scanning x-ray microscope at the 2-ID-B beamline at the Advanced Photon Source for 1-4 keV x-ray imaging and microspectroscopy experiments. The microscope uses a Fresnel zone plate to focus coherent x-ray undulator radiation to a 150 nm focal spot on a sample. The spectral flux in the focus is 10{sup 8} ph/s/0.1% BW. X-ray photons transmitted by the sample are detected by an avalanche photodiode as the sample is scanned to form an absorption image. The sample stage has both coarse and fine translation axes for raster scanning and a rotation axis for microtomography experiments. The incident x-ray beam energy can also be scanned via the 2-ID-B monochromator while the sample is kept in focus to record spatially resolved absorption spectra. We have measured the performance of the instrument with various test objects. The microscope hardware, software, and performance are discussed in this paper.

At the Advanced Photon Source (APS), undulator insertion devices are capable of producing x-ray beams with total power of about 5 kW and normal incidence heat fluxes of about 170 W/mm{sup 2} at 30 m from the source. On beamlines in which the first optical element is a mirror, the reflected beam from the mirror still carries considerable power and power density. Depending on its location, the monochromator downstream of the mirror might be subject to 300 W total power and 5 W/mm{sup 2} normal incidence heat flux. Thus, it is still necessary to carefully design a monochromator that provides acceptable performance under these heat loads. A contact-cooled u-shaped monochromator may be used in this case. The main feature of the u-shaped monochromator is that, by carefully selecting the geometry and cooling locations, is passively corrects for some of the thermally induced crystal distortions. We present experimental and computational results of a contact cooled u-shaped monochromator tested on an APS undulator beamline. The results are encouraging and compare favorably with liquid-gallium internally cooled crystals.

A number of difficult technical challenges need to be solved in the fields of accelerator and free-electron laser (FEL) technologies in order to build an X-ray FEL. One of the tasks well suited to the Advanced Photon Source Low Energy Undulator Test Line (LEUTL) is to take the intermediate step of solving some of the problems of single-pass FEL operation in the ultraviolet range. The existing Advanced Photon Source (APS) linac, in addition to its role of supply positrons for the APS storage ring, will also be used to generate the particle beam for the LEUTL. Here, the design of the magnetic system for the high gain soft x-ray free electron laser is described.

Beam sizes of the stored electron beam at the Advanced Photon Source storage ring were measured using zone-plate optics and undulator radiation. A gold Fresnel zone plate (3.5 {micro}m thick) located 33.9 meters from the x-ray source focused radiation of 18 keV, selected by a cryogenically cooled Si(111) crystal in horizontal deflection, and formed a source image in a transverse plane 2.41 m downstream. The sizes of the source image were determined from measured intensity profiles of x-ray fluorescence from a smooth nickel edge (1.5 {micro}m thick), fabricated using a lithographic technique, while the nickel edge was scanned across over the beam in the transverse plane. The measured vertical and horizontal sizes of the electron beam were 60 {+-} 4.3 {micro}m and 300 {+-} 13 {micro}m, respectively, in reasonable agreement with the expected values.

This paper describes the design, expected performance, and preliminary test results of a contact-cooled monochromator for use on high heat load x-ray beamlines. The monochromator has a cross section in the shape of the letter U. This monochromator should be suitable for handing heat fluxes up to 5 W/square millimeter. As such, for the present application, it is compatible with the best internally cooled crystal monochromators. There are three key features in the design of this monochromator. First, it is contact cooled, thereby eliminating fabrication of cooling channels, bonding, and undesirable strains in the monochromator due to coolant-manifold-to-crystal-interface. Second, by illuminating the entire length of the crystal and extracting the central part of the reflected beam, sharp slope changes in the beam profile and thus slope errors are avoided. Last, by appropriate cooling of the crystal, tangential slope error can be substantially reduced.

Superconducting technology offers the possibility of creating undulators for synchrotron light sources with better performance than conventional hybrid or pure permanent magnet technologies. A superconducting planar undulator is under development at the Advanced Photon Source (APS) with the goal of providing the APS users with higher photon fluxes at higher photon energies. A magnetic design has been developed and several short magnetic structure prototypes have been built. A phase error of less than 2 degrees rms has been achieved without any magnetic shimming. The team is now working on the manufacture of the first full-scale undulator for the APS. The results of the prototype tests are described in this paper. The designs for the superconducting magnet, the cooling system, and the cryostat are presented, as well as the status of the project.

The main features of the vacuum system TNK storage ring and its parameters are discussed. Operating vacuum levels are equal to ∼3×10−9 Torr, a total pumping speed of about 75×103 I/s. The vacuum chamber is made from an aluminum alloy by the hot extrusion method. The SR‐absorber design is also discussed, and the calculation of the middle vacuum level and lifetime is given.

A vacuum system for the Advanced Photon Source elliptical multipole wiggler (EMW) that will operate at a pressure of 10−9 Torr with a storage ring current of 100 mA at 7.0 GeV has been designed and is being fabricated. The major part of the system is a stainless steel chamber with a 66.6 mm by 19.6 mm rectangular cross section. The length of the vacuum chamber is 3100 mm, and the wall thickness is 1.2 mm. Two versions of the vacuum chamber will be produced: with and without distributed nonevaporable getter (NEG) pumping. The version with NEG pumping will have slides on the top and bottom walls to accommodate sintered plates available from SAES. To activate these plates, the entire vacuum chamber will be baked from the outside up to a temperature of 350° C–450 °C. Provision for the baking is included in the design of the vacuum system, its support, and in the EMW itself. The complexity introduced into the design by the need for external activation of the NEG plates is eliminated in the design of the second...