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This paper provides a review of active control strategies used to isolate high-precisionmachines (e.g. telescopes, particle colliders, interferometers, lithography machines or atomic force microscopes) from external disturbances. The objective of this review is to provide tools to develop the best strategy for a given application. Firstly, the main strategies are presented and compared, using single degree of freedom models. Secondly, the case of huge structures constituted of a large number of elements, like particle colliders or segmented telescopes, is considered.
This work includes the creation of a computer model of the superconducting radio frequency cryostat located at the Canadian Light Source (CLS) in Saskatoon, Canada. This cryostat requires careful pressure and level modulation to ensure proper radio frequency control. A detailed mathematical model of the cryostat is generated based on gas and liquid mass balances for a boiling vessel, along with pressure–volume–temperature relations. Model results are compared with experimental data taken from the actual cryostat at the CLS to determine the accuracy of the simulation. Finally, cryostat performance is explored using the model, and it is demonstrated that there are no significant advantages in pressure modulation when reducing the level operating point, and in fact a reduction in operating level slightly increases the maximum value of pressure spikes due to heat loading.
Ground vibration is a key issue for the Shanghai Synchrotron Radiation Facility (SSRF), which is a third-generation light source under commissioning. However, the ground vibration of the SSRF is much larger than other light sources for relatively softer soil and deeper bedrock. More than 1000 piles with 0.6 m diameter down to 48 m underground, and slabs of 1450 mm thickness for the storage ring tunnel and the experiment hall, have been used to attenuate the ground vibration. Measurement results show that these piles and slab have obvious attenuation effect for the vibration induced by nearby vehicles and air conditioners. The coherences with respect to different distances are also carried out.
Beam stability is always a concern in synchrotron light source facilities, and accurate and stable X-ray beam position monitors (XBPM) are key elements in obtaining desired user beam stability. Currently, Advanced Photon Source is preparing to upgrade its facility to increase productivity and to provide better beam stability. For better beam stability, a grazing-incidence insertion device X-ray beam position monitor (GRID-XBPM) is proposed for the insertion device beamline front ends instead of the current photoemission-based XBPM. The design and development of the GRID-XBPM are summarized in this paper including the thermal simulation results of the GRID-XBPM. Thermal and stress analyses show that it withstands the 21 kW total beam power and the peak heat flux of 1684 W mm−2 at a grazing incidence angle of 0.80° using a heat transfer coefficient of 0.010 Wmm−2 °C−1.
Flexures are enjoying a new boom in numerous high-precision and extreme-environment applications. This paper presents some general aspects of flexure design, showing simple principles, and also some subtler issues concerning kinematic design, stiffness compensation, large reduction ratios and rectilinear as well as circular movements.
The storage ring tune measurement system at the Advanced Photon Source (APS) consists of signal pickup and beam excitation drive striplines. Striplines currently installed in the APS storage ring are of a four-blade (inner conductor) design that serves as a beam diagnostic tool and for transverse and longitudinal tune measurements. A new two-blade stripline was designed for the transverse feedback system and to be used for horizontal beam excitation. In this paper, we discuss its mechanical design, assembly procedure, and construction.
Users at the Advanced Photon Source (APS) requested a special purpose undulator that required 456 electromagnetic coils. This paper discusses the design and fabrication techniques used at the APS to build these room-temperature coils. The coils are made from insulated square copper conductor and are vacuum impregnated with epoxy.
X-ray absorbers in the front ends and beamlines of synchrotron light sources are exposed to very high thermal loads. Many facilities, such as the Advanced Photon Source, are investigating upgrades that will further increase the thermal load. The likelihood of exceeding the limit of subcooled critical heat flux (CHF) in these components was examined. The assessment was performed for both currently possible off-normal operational conditions, such as might occur in the event of a failure of multiple safety interlocks, and the anticipated operating conditions that may result from future upgrades. The subcooled CHF values were calculated using empirical equations frequently cited in the literature and then compared with the computed values of the heat flux at the walls of the component cooling channels in cases where the cooling wall temperature exceeded the water saturation temperature at local hydraulic conditions. Having in mind that the great majority of the available empirical correlations were developed for the conditions characteristic for the operation of heat exchangers in the nuclear power industry, the limitations of this approach are discussed and an experimental study of the subcooled CHF values in the conditions similar to those expected in the front-end and beamline components is proposed.
We report the design and construction of an ultrahigh vacuum compatible cryogenic manipulator for angle-resolved photoemission spectroscopy. This design allows six-axis motions in order to measure the band dispersion and Fermi surface of novel electronic materials. Three translational and polar angular motions are implemented by commercial stages. The azimuthal angle of the crystal can be rotated by up to ±90°, and the range of tilt motion varies from 95° to –10°. The sample position is designed at the centre of the above rotation goniometers. The sample holder is cooled using a continuous-flow cryostat. With liquid helium and nitrogen used for the cryostat, the temperature performance of the sample holder is tested and discussed.
At the Diamond Light Source, adaptive bimorph mirrors are extensively used to focus synchrotron light. Piezo crystals embedded in each bimorph mirror expand or contract in response to applied voltages, enabling the curvature of the reflecting surface to adapt to the required form. However, high-grade metrology tools are needed to determine the optimal voltages. The Diamond Optics & Metrology group have implemented in situ (on the beamlines) and ex situ (in a metrology lab) methods of characterizing optical surfaces. For ex situ tests, a slope-measuring profiler (the Diamond-NOM (Nanometre Optical Metrology)) is employed. In situ, X-ray pencil beam scans, performed using an X-ray sensitive camera and software designed in-house, are used to correct optical slope errors. Ex situ and in situ data are shown to be in good agreement. Examples of in situ improvements in the focusing quality and deliberate defocusing are shown. The methods developed are also applicable to many other forms of adaptive optics.
A novel mirror bender system utilizing cam-shaft mover (CSM) with 100 µm eccentricity was designed and successfully tested. The system was initially tested and characterized in the laboratory, and then later the performance was verified using the Advanced Photon Source synchrotron radiation source. The force from the two separate CSMs is translated to both ends of a mirror through a small-diameter bellows feed-through. The system uses an internal spring assembly to compensate for atmospheric pressure. A compact gear box with 10:1 ratio between the stepper motor and cam shaft is used to increase the precision of the bender system. This bender system is equipped with a precise rotary potentiometer and load cell for feedback. A system resolution better than 0.2 µm per step was achieved. This bender system was designed as a separate unit, is very compact and can be used to bend a mirror in both the vertical and horizontal planes. Details of the system design, changes made from the prototype system to the production unit and test results are presented here.
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.
As part of phase 1 of the European synchrotron radiation facility (ESRF) upgrade programme, a new beamline (UPBL6) for the study of electronic excitations using inelastic scattering and emission spectroscopy will be designed and constructed. The new beamline will provide an intense stable X-ray beam at two different spectrometers to be used on a time-shared basis. One of the spectrometers will be dedicated to resonant inelastic X-ray scattering (RIXS); the other to X-ray Raman spectroscopy (XRS). This beamline is currently (June 2010) in the design phase and may be fully operational by early 2013.
The in-vacuum undulator (IVU) controller has been developed and applied in Shanghai Synchrotron Radiation Facility (SSRF), China. The controller based on programmable logic controller (PLC) mainly controls two stepper motors for regulating the gap and taper of magnet array, implement automatic control of the correction coil power supplies, etc. In addition, the controller is also provided with a local and remote working mode. This paper mainly introduces related hardware and software design for the IVU controller.
Polychromators, or elliptically bent diffracting crystals that focus a broad-bandwidth X-ray beam onto a sample, have become a common device at synchrotron beamlines specializing in X-ray absorption spectroscopy (XAS) because they allow a full absorption spectrum to be collected in one shot. Such a device is being planned for the XAS beamline I20 of the Diamond Light Source. A bent silicon crystal diffracting 7 keV X-rays with the (1 1 1) reflection is taken as a model for the simulations of this report. Instrumental resolution is determined by the demagnification of the source, the spread of the diffracted beam during propagation and the pixel size of the position-sensitive detector placed behind the sample. The first is calculated by geometrical optics. The second is calculated by a full wave-optical treatment, which includes Takagi–Taupin integration to find the diffracted amplitude at the crystal's surface and Huygens–Fresnel propagation of the diffracted wave to the sample or detector. This sets the polychromator's intrinsic energy resolution. The pixel size of the detector is then added to find the total instrumental resolution at various sample–detector distances.
The 3 GeV Taiwan Photon Source (TPS) is designed to produce an electron beam with small emittance and to be maintained with top-up operation. The vacuum systems of the TPS-pulsed magnets in the storage ring include four kicker ceramic chambers for the stored beam and an injection chamber for the injected beam. The prototypical design, manufacturing process and some test results for these chambers are described.
The National Synchrotron Light Source II currently under construction at the Brookhaven National Laboratory is expected to provide unprecedented orbit stability in the storage ring in order to fully utilize the very small emittance of the electron beam. The desire to measure the position of such small beams to high resolution imposes stringent requirements on the thermal and structural stability of the supports for the beam postion monitor (BPM) pick-up electrodes located on multi-pole vacuum chambers and more so on those located upstream and downstream of insertion device sources where the beam size is the smallest. Even with tunnel air temperature expected to be controlled to ±0.1°C, low coefficient of thermal expansion materials is required to meet this level of thermal stability. Here, we present the application of these materials to the design of stable supports for radio frequency (RF)-BPMs as well as the methods of testing their performance.
National Synchrotron Light Source II (NSLS-II), a new state-of-the-art third-generation light source under construction at Brookhaven National Laboratory is expected to have extremely small emittance and extraordinary beam stability. The mechanical requirements for beam diagnostics and instrumentation are exceptionally challenging. Here we present an overview of the mechanical aspects of some NSLS-II diagnostics as well as the performance levels of some systems currently under development.
The FERMI@ELETTRA Free-Electron-Laser (FEL) project at the ELETTRA Laboratory of Sincrotrone Trieste, currently under construction and commissioning, will comprise a linear accelerator and two FEL beamlines. Two identical magnetic chicanes for bunch length compression will be installed in the linear accelerator (LINAC) tunnel. The first bunch compressor, at 300 MeV, has been recently installed and commissioned while the production and installation plan of the second one (at 600 MeV) is being defined. The chicane mechanical design has been achieved in collaboration with the supplier, Rial Vacuum srl. In this paper, the chicane mechanical design and the movable vacuum chambers are presented.
Two in-vacuum undulators (IVU25) have been used since March 2009 at the Shanghai Synchrotron Radiation Facility. Another small-gap in-vacuum undulator with a smaller period length of 20 mm was completed in July 2010. The mechanical system of IVU25 consists of support frame, driving and guiding system, taper mechanism, compensation spring system, suspending rods assembly, etc. We have attempted to manufacture IVU25 with high mechanical stability, rigidity and reproducible gap motion. A mechanical design study of IVU25 is carried out which includes finite-element calculations on the mechanical deformation of the girder. Some modifications have been made to the design of IVU20.