Third-generation Storage Ring Research Articles

Three-pole wigglers at NSLS-II

The National Synchrotron Light Source-II (NSLS-II) at Brookhaven National Lab (BNL) is a third-generation medium-energy storage ring with 3 GeV and sub-nm-rad horizontal emittance, equipped with a top-off capability of 500 mA. It is designed to deliver an extremely intense photon beam across a wide spectral range, from the far-infrared to the very hard X-ray region. This outstanding performance is achieved through a combination of bending magnets (BM), three-pole wigglers (3 PW), and advanced insertion device (ID) sources. Six three-pole wigglers have been constructed at the NSLS-II IDs Lab. These devices are used to produce broadband radiation with lower angular power density and to monitor the electron beam emittance and energy spread. This paper describes the R&D activities focused on developing the required magnetic and mechanical designs, along with magnetic field optimization and the final magnetic measurement results. It also covers the spectral brightness, flux, power density, spatial and angular output properties of the 3 PWs, including their commissioning results and their effects on the performance of the NSLS-II storage ring.

Storage rings in Korea as synchrotron radiation source

Remarkable progress has been made in photon beam brightness from storage rings. From the early 90’s, third-generation storage rings (3GSRs) have been put into operation and have provided very bright photon beams using insertion devices. Fourth-generation storage rings (4GSRs) that exploit the multi-bend achromat lattice concept may be able to surpass the brightness and coherence that have been attained using present third-generation storage rings. Recently, a 4GSR project was officially approved to meet the increasing demand from the growing user community in Korea. This paper describes progress in the development of storage rings in Korea, including the status and the plans for PLS-II, and the results on the conceptual design for Korea-4GSR.

Characteristics of Photon Beam and Preservation of Coherence in Fourth-Generation Light Sources

Fourth-generation storage rings (4GSRs) that exploit the multi-bend achromat lattice concept may be able to surpass the brightness and coherence that are attained using the present third-generation storage rings. This paper presents the characteristics of photon beams and an analysis of their coherence properties in Korea-4GSR to represent 4GSRs.

Comparison of photon beam characteristics of Korea-4GSR with PLS-II

The Korea fourth-generation storage ring (Korea-4GSR), with 4-GeV beam energy and 58-pm-rad emittance has been designed by the Pohang Accelerator Laboratory. The evaluated brilliance and coherence are approximately 100 times higher in the hard X-ray region in Korea-4GSR than in the third-generation storage ring at PLS-II. The coherence properties and preservation of coherence through beamline optical elements were studied using SPECTRA code and hybrid method. Result of this paper show essential information for planning experiments and designing beamlines using ultimate low emittance storage ring.

Compact IR synchrotron beamline design.

Third-generation storage rings are massively evolving due to the very compact nature of the multi-bend achromat (MBA) lattice which allows amazing decreases of the horizontal electron beam emittance, but leaves very little place for infrared (IR) extraction mirrors to be placed, thus prohibiting traditional IR beamlines. In order to circumvent this apparent restriction, an optimized optical layout directly integrated inside a SOLEIL synchrotron dipole chamber that delivers intense and almost aberration-free beams in the near- to mid-IR domain (1-30 µm) is proposed and analyzed, and which can be integrated into space-restricted MBA rings. Since the optics and chamber are interdependent, the feasibility of this approach depends on a large part on the technical ability to assemble mechanically the optics inside the dipole chamber and control their resulting stability and thermo-mechanical deformation. Acquiring this expertise should allow dipole chambers to provide almost aberration-free IR synchrotron sources on current and `ultimate' MBA storage rings.

Demonstration of narrowband X-ray beam by inverse Compton scattering with stored spontaneous emission

We achieved the generation of narrowband X-ray beams by inverse Compton scattering using stored spontaneous emission and electron bunches in the infrared free-electron laser system of the storage ring NIJI-IV. Using stored spontaneous emission with a resonant wavelength of 1530 nm and an electron beam with an energy of 310 MeV, an X-ray beam with the energy spread of approximately 10% and the Compton edge of 1.2 MeV was observed using a LaBr3(Ce) scintillation detector in the 3-bunch operation. X-ray beams were generated by inverse Compton scattering using stored spontaneous emission in the full-bunch (16-bunch) operation, and an increase in the bunch number is shown to be effective for increasing the Compton X-ray yield. The total yield of the Compton X-ray beam reached 3.1 × 104 photons/s at the electron-beam current of 43.5 mA in the full-bunch operation. These experimental results are likely to be useful for the development of narrowband X-ray beams with energies above 1 MeV, for use in energy recovery linacs and third-generation storage rings.

Emittance and lifetime measurement with damping wigglers.

National Synchrotron Light Source II (NSLS-II) is a new third-generation storage ring light source at Brookhaven National Laboratory. The storage ring design calls for small horizontal emittance (<1 nm-rad) and diffraction-limited vertical emittance at 12 keV (8 pm-rad). Achieving low value of the beam size will enable novel user experiments with nm-range spatial and meV-energy resolution. The high-brightness NSLS-II lattice has been realized by implementing 30-cell double bend achromatic cells producing the horizontal emittance of 2 nm rad and then halving it further by using several Damping Wigglers (DWs). This paper is focused on characterization of the DW effects in the storage ring performance, namely, on reduction of the beam emittance, and corresponding changes in the energy spread and beam lifetime. The relevant beam parameters have been measured by the X-ray pinhole camera, beam position monitors, beam filling pattern monitor, and current transformers. In this paper, we compare the measured results of the beam performance with analytic estimates for the complement of the 3 DWs installed at the NSLS-II.

Vibration measurements of high-heat-load monochromators for DESY PETRA III extension.

The requirement for vibrational stability of beamline optics continues to evolve rapidly to comply with the demands created by the improved brilliance of the third-generation low-emittance storage rings around the world. The challenge is to quantify the performance of the instrument before it is installed at the beamline. In this article, measurement techniques are presented that directly and accurately measure (i) the relative vibration between the two crystals of a double-crystal monochromator (DCM) and (ii) the absolute vibration of the second-crystal cage of a DCM. Excluding a synchrotron beam, the measurements are conducted under in situ conditions, connected to a liquid-nitrogen cryocooler. The investigated DCM utilizes a direct-drive (no gearing) goniometer for the Bragg rotation. The main causes of the DCM vibration are found to be the servoing of the direct-drive goniometer and the flexibility in the crystal cage motion stages. It is found that the investigated DCM can offer relative pitch vibration down to 48 nrad RMS (capacitive sensors, 0-5 kHz bandwidth) and absolute pitch vibration down to 82 nrad RMS (laser interferometer, 0-50 kHz bandwidth), with the Bragg axis brake engaged.

Microfocusing options for the inelastic X-ray scattering beamline at sector 3 of the Advanced Photon Source.

Synchrotron radiation from third-generation high-brilliance storage rings is an ideal source for X-ray microbeams. The aim of this paper is to describe a microfocusing scheme that combines both a toroidal mirror and Kirkpatrick-Baez (KB) mirrors for upgrading the existing optical system for inelastic X-ray scattering experiments at sector 3 of the Advanced Photon Source. SHADOW ray-tracing simulations without considering slope errors of both the toroidal mirror and KB mirrors show that this combination can provide a beam size of 4.5 µm (H) × 0.6 µm (V) (FWHM) at the end of the existing D-station (66 m from the source) with use of full beam transmission of up to 59%, and a beam size of 3.7 µm (H) × 0.46 µm (V) (FWHM) at the front-end of the proposed E-station (68 m from the source) with a transmission of up to 52%. A beam size of about 5 µm (H) × 1 µm (V) can be obtained, which is close to the ideal case, by using high-quality mirrors (with slope errors of less than 0.5 µrad r.m.s.). Considering the slope errors of the existing toroidal and KB mirrors (5 and 2.9 µrad r.m.s., respectively), the beam size grows to about 13.5 µm (H) × 6.3 µm (V) at the end of the D-station and to 12.0 µm (H) × 6.0 µm (V) at the front-end of the proposed E-station. The simulations presented here are compared with the experimental measurements that are significantly larger than the theoretical values even when slope error is included in the simulations. This is because of the experimental set-up that could not yet be optimized.

Optics matching schemes for linac-based light source

Despite its small average beam current limit, a linac has features that make it attractive as an X-ray source: high energy, ultra-low emittance and energy spread, and flexible beamline optics. Unlike a storage ring, in which an undulator radiation source necessarily is short and positioned at the electron beam waist, in a linac the undulator can be long and the electron beam can be adjustable to have a virtual waist far downstream towards the X-ray target to produce a convergent X-ray beam. Using a planned CEBAF beamline as an example, we show here that we can overcome a factor of 2000 in the beam current to produce a monochromatic hard X-ray source comparable with, or even exceeding, the performance of an X-ray line at a third-generation storage ring. Even with no monochromator, the X-ray energy bandwidth can be as small as 0.1%. We discuss the optimal conditions which produce maximum X-ray flux density by focusing the electron beam for twocases: one is based on the waist-at-target (WAT) scheme, while the other goes beyond the WAT scheme. Both cases were verified by simulations using the SRW code.

IR and X-ray time-resolved simultaneous experiments: an opportunity to investigate the dynamics of complex systems and non-equilibrium phenomena using third-generation synchrotron radiation sources

Third-generation storage rings are modern facilities working with high currents and designed to host powerful radiation sources, like undulators and wigglers, and to deliver high-brilliance beams to users. Many experiments at high spatial resolution, such as spectromicroscopy at the nanometre scale and with high temporal resolution to investigate kinetics down to the picosecond regime, are now possible. The next frontier is certainly the combination of different methods in a unique set-up with the ultimate available spatial and temporal resolutions. In the last decade much synchrotron-based research has exploited the advantage of complementary information provided by time-resolved X-ray techniques and optical methods in the UV/Vis and IR domains. New time-resolved and concurrent approaches are necessary to characterize complex systems where physical-chemical phenomena occur under the same experimental conditions, for example to detect kinetic intermediates via complementary but independent observations. In this contribution we present scientific cases from original works and literature reviews to support the proposed IR/X-ray simultaneous approach, with both probes exploiting synchrotron radiation sources. In addition, simple experimental layouts that may take advantage of the high brilliance and the wide spectral distribution of the synchrotron radiation emission will be given for specific researches or applications to investigate dynamic processes and non-equilibrium phenomena occurring in many condensed matter and biological systems, of great interest for both fundamental research and technological applications.

Thermo-mechanical analyses of beryllium compound refractive lens for NSLS-II beamline

In this paper we discuss the finite-element analysis (FEA) of a one-dimensional beryllium compound refractive lens (Be-CRL) that was undertaken to study the feasibility of installing the CRL in the Inelastic X-ray Scattering (IXS) beamline of National Synchrotron Light Source-II (NSLS-II) (a new state-of-the-art medium-energy third-generation storage ring). The current insertion device for this beamline is an IVU22-6m in-vacuum planar undulator delivering a total power of ~9 kW with a peak power density of ~90 kW/mrad2. Through analysis, based on calculation of spectral angular distribution of undulator radiation from IVU22, we determined that it is essential to install a 30 µm graphite filter upstream of the CRL in order to restrict the temperature rise in the CRL to 65°C for acceptable thermal strain.

Stability of NSLS-II girder–magnet assembly

The low-emittance design of the NSLS-II (a new state-of-the-art medium energy third-generation storage ring) requires that the uncorrelated vertical RMS motion between the multipole magnets on a girder be less than 25 nm. The stability of the girder–magnet assembly is affected by factors such as ambient vibration, temperature fluctuations and diurnal floor motion in the storage ring. In this paper we discuss the design features of a high-stability girder–magnet assembly for the NSLS-II.

High-accuracy radiometry in the EUV range at the PTB soft x-ray beamline

During the past decade, high-accuracy soft x-ray radiometry has increasingly gained in importance. In particular, its routine availability is a prerequisite for the development of extreme UV lithography (EUVL). The PTB has been providing EUV calibration services for many years at a dedicated radiometry beamline at the electron storage ring BESSY I and from the year 2000 at the new PTB synchrotron radiation laboratory at BESSY II. Reflectometry, especially the measurement of the reflectance of Mo/Si multilayer mirrors for EUVL, is a major activity at the beamline. As the performance of the third-generation storage ring BESSY II is better than that of BESSY I, the measurement uncertainties could be significantly reduced. Efforts were made to accurately determine the wavelength scale for the monochromator and to suppress diffusely scattered light. For the spectral reflectance of a mirror in the EUV spectral region, a relative uncertainty of u = 0.14% is achieved. A new reflectometer will enable PTB to characterize EUVL optics up to 550 mm in diameter and 50 kg in mass. Detector calibration is based on a primary detector standard, a cryogenic electrical substitution radiometer. Photodiodes with a nearly constant spectral responsitivity in the soft x-ray range are calibrated as transfer detector standards with a relative uncertainty of u = 0.26% by direct comparison to the radiometer.

Radiometry with synchrotron radiation

Electron storage rings are nearly ideal radiation sources for radiometry over a broad spectral range from the infrared to the x-ray region. Many national metrology institutes make extensive use of synchrotron radiation for radiometry. The Synchrotron Ultraviolet Radiation Facility SURF III, which has recently been upgraded, is used by the National Institute of Standards and Technology (NIST), and the Physikalisch-Technische Bundesanstalt (PTB) operates a European radiometry laboratory at the third-generation storage ring BESSY II. The storage rings are used as calculable broadband radiation sources (primary source standards) and in combination with primary detector standards as sources of continuously tunable monochromatic radiation for detector calibration. The use of cryogenic electrical-substitution radiometers as primary detector standards has made it possible to considerably extend high-accuracy calibrations from the ultraviolet (UV) to the x-ray regime. Radiometry in the extreme UV (EUV) range, and in particular reflectometry, has become increasingly important for the development of EUV lithography. An overview of synchrotron radiation based radiometry will be given.

Basic Characteristics of Synchrotron Radiation

Many advances have been made in chemical structure research over the past three decades using synchrotron radiation. Synchrotron radiation has a number of unique properties. They include high brightness, high collimation, broad energy spectrum, variable polarization, coherent power, and subnanosecond pulse width. The third-generation storage rings with wiggler and undulator sources and lower electron beam dimensions are delivering over 1012 times higher brightness than laboratory-based sources. The future of synchrotron sources looks very promising with the development of energy recovery linac sources and free-electron laser sources. These will permit dynamic studies of chemical structure with subpicosecond time resolution. Commensurate with the development of X-ray sources, major progress has occurred in optical schemes to meet the challenging needs of chemical structure research. High-resolution monochromatization and submicron focusing of X rays present new avenues for the future.

Energy recovery linacs as synchrotron radiation sources (invited)

Practically all synchrotron x-ray sources to data are based on the use of storage rings to produce the high current electron (or positron) beams needed for synchrotron radiation (SR). The ultimate limitations on the quality of the electron beam, which are directly reflected in many of the most important characteristics of the SR beams, arise from the physics of equilibrium processes fundamental to the operation of storage rings. It is possible to produce electron beams with superior characteristics for SR via photoinjected electron sources and high-energy linacs; however, the energy consumption of such machines is prohibitive. This limitation can be overcome by the use of an energy recovery linac (ERL), which involves configuring the electron-beam path to use the same superconducting linac as a decelerator of the electron beam after SR production, thereby recovering the beam energy for acceleration of new electrons. ERLs have the potential to produce SR beams with brilliance, coherence, time structure, and source size and shape which are superior to even the best third-generation storage ring sources, while maintaining flexible machine operation and competitive costs. Here, we describe a project to produce a hard x-ray ERL SR source at Cornell University, with emphasis on the characteristics, promise, and challenges of such an ERL machine.

Self-amplified spontaneous emission saturation at the Advanced Photon Source free-electron laser (abstract) (invited)

Today, many bright photon beams in the ultraviolet and x-ray wavelength range are produced by insertion devices installed in specially designed third-generation storage rings. There is the possibility of producing photon beams that are orders of magnitude brighter than presently achieved at synchrotron sources, by using self-amplified spontaneous emission (SASE). At the Advanced Photon Source (APS), the low-energy undulator test line (LEUTL) free-electron laser (FEL) project was built to explore the SASE process in the visible through vacuum ultraviolet wavelength range. While the understanding gained in these experiments will guide future work to extend SASE FELs to shorter wavelengths, the APS FEL itself will become a continuously tunable, bright light source. Measurements of the SASE process to saturation have been made at 530 and 385 nm. A number of quantities were measured to confirm our understanding of the SASE process and to verify that saturation was reached. The intensity of the FEL light was measured versus distance along the FEL, and was found to flatten out at saturation. The statistical variation of the light intensity was found to be wide in the exponential gain region where the intensity is expected to be noisy, and narrower once saturation was reached. Absolute power measurements compare well with GINGER simulations. The FEL light spectrum at different distances along the undulator line was measured with a high-resolution spectrometer, and the many sharp spectral spikes at the beginning of the SASE process coalesce into a single peak at saturation. The energy spread in the electron beam widens markedly after saturation due to the number of electrons that transfer a significant amount of energy to the photon beam. Coherent transition radiation measurements of the electron beam as it strikes a foil provide additional confirmation of the microbunching of the electron beam. The quantities measured confirm that saturation was indeed reached. Details are given in Milton et al., Science 292, 2037 (2001) (also online at www.sciencexpress.org as 10.1126/science. 1059955, 17 May 2001), and Lewellen et al., “Present Status and Recent Results from the APS SASE FEL,” to be published in the Proceedings of the 23rd International Free-Electron Laser Conference, Darmstadt, Germany, 20–24 August 2001.

Beam stability at light sources (invited)

The level of photon beam stability required in an experiment to meet measurement resolution goals depends on the experiment-specific photon phase space acceptance and the sensitivity of measurement to electron beam motion within its six-dimensional phase space. Stability time scales range from hours to microseconds, depending on experiment sampling rate, data integration period, and scan duration. Meeting these requirements at third-generation storage ring light sources can imply micron and submicroradian electron orbit stability and energy (ΔE/E) oscillation amplitudes in the part-per-million range, presenting a formidable challenge for accelerator designers. Beam stability criteria, measures taken to meet them, and achievable levels of stability in present and future light sources, are reviewed.

The historical development of cryogenically cooled monochromators for third-generation synchrotron radiation sources

In the period of the late-1980s, before the construction of multi-GeV third-generation storage rings with their intense insertion-device sources, the perceived number one problem for X-ray instrumentation was proper cooling of the first optical element in the beamline. This article, first given as an acceptance speech for the Compton Award ceremony at the Advanced Photon Source, presents a somewhat historical and anecdotal overview of how cryogenically cooled monochromator optics have been developed to provide a monochromator cooling solution adequate for today's power levels. A series of workshops and international collaborations were the key components for the progress and final success of this development.