GeV Taiwan Photon Source Research Articles

An integrated system for user-friendly X-ray intensity attenuation in a wide energy range

For undulator hard X-ray beamlines of a wide energy range, the beam intensity control is often needed to regulate the photon flux impinging on delicate detectors. Despite the capability of state-of-the-art X-ray pixel detectors being greatly advanced recently, the frontier undulator beamlines in synchrotron facilities often carry outstanding photon fluxes that are sometimes too high for certain measurements. Here, we report a developed protocol that allows intensity attenuation of an X-ray beam in the 4-23 keV energy range with flexible attenuation factors; a prototype is installed and tested on the 13A biological small-angle X-ray scattering beamline of the 3 GeV Taiwan Photon Source (TPS) of the National Synchrotron Radiation Research Center, Hsinchu, Taiwan. The intensity attenuation system is modified from a commercially available pneumatically actuated, vacuum-type precision X-ray attenuator of ADC ABS-300; the system provides beam attenuation factors covering 8 orders of intensity attenuation for an X-ray beam in 4-23 keV. This was achieved with selected combinations of 10 sets of metal foils comprising different thicknesses of Al, Ti, Cu, and Ta foils. A user-friendly protocol is established to automatically compare a subscribed attenuation factor with all the possible attenuation factors from the 1024 combinations of the 10 sets of foils in the X-ray energy used, and determine a set of the metal foils having a best-matched attenuation factor. Calculation of beam intensity attenuations with the selected foils is coded with Python and integrated into the Experimental Physics and Industrial Control System (EPICS). The input of an attenuation factor is done through a graphical display of the attenuator system based on the Control System Studio (CSS). The developed X-ray beam attenuation system provides a convenient and intuitive beam intensity control and has the potential to be adopted in future beamlines.

Performance of the new biological small- and wide-angle X-ray scattering beamline 13A at the Taiwan Photon Source.

Recent developments in the instrumentation and data analysis of synchrotron small-angle X-ray scattering (SAXS) on biomolecules in solution have made biological SAXS (BioSAXS) a mature and popular tool in structural biology. This article reports on an advanced endstation developed at beamline 13A of the 3.0 GeV Taiwan Photon Source for biological small- and wide-angle X-ray scattering (SAXS-WAXS or SWAXS). The endstation features an in-vacuum SWAXS detection system comprising two mobile area detectors (Eiger X 9M/1M) and an online size-exclusion chromatography system incorporating several optical probes including a UV-Vis absorption spectrometer and refractometer. The instrumentation and automation allow simultaneous SAXS-WAXS data collection and data reduction for high-throughput biomolecular conformation and composition determinations. The performance of the endstation is illustrated with the SWAXS data collected for several model proteins in solution, covering a scattering vector magnitude q across three orders of magnitude. The crystal-model fittings to the data in the q range ∼0.005-2.0 Å-1 indicate high similarity of the solution structures of the proteins to their crystalline forms, except for some subtle hydration-dependent local details. These results open up new horizons of SWAXS in studying correlated local and global structures of biomolecules in solution.

Optical design and performance of the biological small-angle X-ray scattering beamline at the Taiwan Photon Source.

The optical design and performance of the recently opened 13A biological small-angle X-ray scattering (SAXS) beamline at the 3.0 GeV Taiwan Photon Source of the National Synchrotron Radiation Research Center are reported. The beamline is designed for studies of biological structures and kinetics in a wide range of length and time scales, from angstrom to micrometre and from microsecond to minutes. A 4 m IU24 undulator of the beamline provides high-flux X-rays in the energy range 4.0-23.0 keV. MoB4C double-multilayer and Si(111) double-crystal monochromators (DMM/DCM) are combined on the same rotating platform for a smooth rotation transition from a high-flux beam of ∼4 × 1014 photons s-1 to a high-energy-resolution beam of ΔE/E ≃ 1.5 × 10-4; both modes share a constant beam exit. With a set of Kirkpatrick-Baez (KB) mirrors, the X-ray beam is focused to the farthest SAXS detector position, 52 m from the source. A downstream four-bounce crystal collimator, comprising two sets of Si(311) double crystals arranged in a dispersive configuration, optionally collimate the DCM (vertically diffracted) beam in the horizontal direction for ultra-SAXS with a minimum scattering vector q down to 0.0004 Å-1, which allows resolving ordered d-spacing up to 1 µm. A microbeam, of 10-50 µm beam size, is tailored by a combined set of high-heat-load slits followed by micrometre-precision slits situated at the front-end 15.5 m position. The second set of KB mirrors then focus the beam to the 40 m sample position, with a demagnification ratio of ∼1.5. A detecting system comprising two in-vacuum X-ray pixel detectors is installed to perform synchronized small- and wide-angle X-ray scattering data collections. The observed beamline performance proves the feasibility of having compound features of high flux, microbeam and ultra-SAXS in one beamline.

Ultrahigh Vacuum Technologies Developed for a Large Aluminum Accelerator Vacuum System

A large particle accelerator requires an ultrahigh vacuum (UHV) system of average pressure under <TEX>$1{\times}10^{-7}$</TEX> Pa for mitigating the impact of beam scattering from the residual gas molecules. The surface inside the beam ducts should be controlled with an extremely low thermal outgassing rate under <TEX>$1{\times}10^{-9}Pa{\cdot}m^3/(s{\cdot}m^2)$</TEX> for the sake of the insufficient pumping speed. To fulfil the requirements, the aluminum alloys were adopted as the materials of the beam ducts for large accelerator that thanks to the good features of higher thermal conductivity, non-radioactivity, non-magnetism, precise machining capability, et al. To put the aluminum into the large accelerator vacuum systems, several key technologies have been developed will be introduced. The concepts contain the precise computer numerical control (CNC) machining process for the large aluminum ducts and parts in pure alcohol and in an oil-free environment, surface cleaning with ozonized water, stringent welding process control manually or automatically to form a large sector of aluminum ducts, ex-situ baking process to reach UHV and sealed for transportation and installation, UHV pumping with the sputtering ion pumps and the non-evaporable getters (NEG), et al. The developed UHV technologies have been applied to the 3 GeV Taiwan Photon Source (TPS) and revealed good results as the expectation. The problems of leakage encountered during the assembling were most associated with the vacuum baking which result in the consequent trouble shootings and more times of baking. Then the installation of the well-sealed UHV systems is recommended.

Aluminium ultrahigh vacuum system for the 3 GeV TPS synchrotron light source

The 3-GeV Taiwan Photon Source (TPS) is a large accelerator and synchrotron light source of circumference 518.4 m. The electron storage ring of TPS requires an ultrahigh-vacuum pressure per beam current less than 2×10−10 Pa/mA in the beam duct to maintain a long life of the circulating beam without scattering of ions by residual gases. Aluminium alloys used for the beam ducts have a benefit of greater thermal conductivity that simplifies the structure of vacuum vessels built with the cooling components. Machining completely free of oil applied to the aluminium chambers followed by cleaning with ozonized water and welding in house provide a precise dimensional control within 0.3 mm and a clean surface with a small rate ~ 6.4×10−12 Pa m/s of thermal outgassing after baking at 150 °C for 24 h. The assembled ion pump with non-evaporable getter pump is capable of evacuating the chamber to a pressure < 1×10−9 Pa. The average pressure inside the duct is expected to be sufficiently small. The clean process to manufacture the aluminium ultrahigh vacuum system is described.

Fabrication of one-cell vacuum system for Taiwan Photon Source

A vacuum system of 3 GeV Taiwan photon source (TPS, with circumference 518.4 m), is designed for low-outgassing aluminium beam ducts, low-impedance structure, oil-less pumping system and oil-less fabrication. A prototype (total length 14 m) of the TPS vacuum system has been fabricated. This one-cell prototype vacuum system consists of two bending-magnet chambers (~4 m long each), two straight chambers (~3 m long each), supporting stands, five beam positioning monitors and pumps. Two bending-magnet chambers were made by computer-numerical control machining, which was lubricated with ethanol to protect the surface from oil contamination. Next, these two bending chambers were cleaned with ozonated water to decrease the rate of thermal outgassing and photo-stimulated desorption. The rest chambers were also cleaned by chemical cleaning method. An automatic welding system then was used to implement the side-welding seams of bending chambers in a temperature- and humidity-controlled cleanroom. The bending and straight chambers were welded into one piece by ‘on-site welding’. After baking at 150°C for 24 h, an optimizing pressure could be achieved at 4.9 nPa.

Numerical simulation and mock-up experimental measurement of the air conditioning system for the 3 GeV Taiwan Photon Source electron storage ring

National Synchrotron Radiation Research Center, Taiwan, is currently constructing the civil buildings and utility system of the Taiwan Photon Source. The air conditioning (AC) system of the storage ring tunnel was designed based on those of existing Taiwan Light Source and some international advanced accelerators. To predict the air temperature variation and flow pattern in tunnel more precisely, we applied 3D computational fluid dynamics scheme and built up a one-cell mock-up equipped with AC system. In the 3D numerical model, effects of magnets of the booster and the storage ring, girders, cable trays, front ends and the supplied air wind duct are all taken into account. The temperature variations and flow pattern were shown through the numerical simulation. Measured air temperature data in the one-cell mock-up were also collected.

Vacuum system of a Taiwan photon source-pulsed magnet

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.

Computer simulation of bunch lengthening effects caused by a third harmonic cavity in conjunction with deflecting cavities in 3 GeV Taiwan Photon Source

The effects of utilizing a third harmonic RF cavity in thelengthening mode have been investigated by computer simulation onquality of the electron beam as well as the emitted photons in thedeflecting RF structures for TPS. For the obtained optimumsynchronous and relative harmonic phases with a harmonic voltage of0.472 MV the Touschek lifetime increases by around 8 hours. For theextreme operation mode of deflectors (h=8 and 6 MV deflectingvoltage) the eventual horizontal and vertical emittancesdramatically blows up to 3.07 nm-rad and 85 pm-rad, respectively. Inaddition, no significant difference in duration of the radiatedpulses between operation of the main and the third harmonic RFcavities is observed. The results show that the intensity of theemitted X-ray pulses with a 0.5 ps FWHM reduces by 10% for thedouble RF operation in TPS.

Vacuum system of the 3 GeV Taiwan photon source

The design and a prototype of the vacuum system of a low-emittance 3 GeV synchrotron light source, the Taiwan photon source (TPS) (with circumference of 518.4 m), are described. The TPS vacuum system has low-outgassing aluminum beam ducts, a low-impedance structure, an oil-less pumping system, and oil-less fabrication. Little dust, a stable mechanical structure, and highly reliable components are achieved for this vacuum system. A prototype (length 14 m) of the TPS vacuum system was fabricated. Two bending-magnet chambers, 4 m long, were made with computer-numerical control machining and lubricated with ethanol to protect the aluminum surface from oil contamination. Cleaning with ozonized water was applied to decrease the rate of photostimulated desorption from the chamber surfaces. Then an automatic welding system is used to implement the side welding seams of bending chambers. The design considerations, the critical factors in fabrication, and the test results of the vacuum system prototype are presented.

Utilization of transverse deflecting RF cavities in the designed QBA lattice of 3 GeV Taiwan Photon Source

A pair of superconducting transverse deflecting RF cavities has been studied in the QBA low emittance lattices of 3 GeV TPS for generating ultra short X-ray pulses. Three configurations with different locations for the two cavities in a super-period of the TPS ring are investigated. During numerous turns of the electron tracking, the nonlinear effects between the cavities, the energy spread, the momentum compaction factor, and the synchrotron radiation effects are taken into account. The configuration with positioning the RF deflectors between the QBA cells in each super-period as an optimum arrangement gives rise to better quality electron bunches and radiated photon pulses. The FWHM of the radiated photon pulses of about 540 fs with an acceptable intensity is attained by optimizing the compression optical elements of the TPS photon beam line. Furthermore, the effects of the electron bunch length are studied by alternatively employing an accelerating RF cavity operating with 1.1 MV and 3.0 MV, respectively. The operation of the accelerating RF cavity at 3.0 MV improved the intensity of the photon pulses up to 30% and reduced the equilibrium vertical emittance down to 70 pm-rad. The error tolerance for the deflecting cavities, QBA lattice and injection process are also evaluated.

Vacuum design for the 3 GeV TPS synchrotron light source

The 3 GeV Taiwan Photon Source (TPS) is a synchrotron light accelerator which is designed for a beam emittance of < 2 nmrad at a beam current of 400 mA. The vacuum system for the electron storage ring provides a pressure of < 1 nTorr for the electron beam with long beam life time and small disturbance from trapped ions. Due to the limited space for the pumps and the poor conductance of the beam ducts, the vacuum chambers should be manufactured with a clean surface of very low outgassing rate. Aluminum alloys vacuum chambers and the structures of confined-pumping for the localized photo-desorption are selected to meet the design requirement. The CNC-machining for the bending chambers in pure alcohol spraying, followed by ozonated water cleaning and TIG welding in clean room, provides a clean surface and simple structure which lowers the outgassing rate and the chamber impedance. Combinations of the lumped non-evaporable getters (NEG) and the sputtering ion pumps are located near the absorbers for higher efficiency of localized pumping capability. Either the NEG-strips or interior NEG-coating will be used for the Undulator chambers for providing a good linear pumping feature. The design concept will be described in this paper. Besides, the simulation of the pressure distribution and some test results of outgassing measurement for the aluminum chambers will be discussed.

Design, Construction, and Performance Testing of a 6.5 T Superconducting Wavelength Shifter

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A compact three-pole superconducting magnet with an aluminum warm beam duct was designed and fabricated as an X-ray source in a 1.5 GeV Taiwan Light Source (TLS) or the 3 GeV Taiwan Photon Source (TPS). Three pairs of racetrack NbTi superconducting coils were connected to one main power supply to create a central field of over 6.5 T. Two low current trim power supplies were connected in parallel to the two side pairs of the coil to eliminate the first and second field integrals. The wavelength shifter magnet was cooled in a pool boiling helium bath. Helium boils off at 1.3 L/hr. The vapor-cooled current lead is used to pass the 350 A excitation current. The magnetic field strength was measured at room temperature using a Hall probe and a stretched wire system. The magnet was tested successfully to 308 A, at which the central field exceeded 6.5 T, and the peak field on coil was 8.2 T. The design and construction of the magnet and the cryostat, the quenching protection, and field measurement results will be presented and discussed. </para>