D. J. Wang

National Synchrotron Radiation Research Center (NSRRC), Hsin-chu-hsien, Taiwan, Taiwan

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Publications (51)16 Total impact

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    ABSTRACT: The design, construction and commissioning of a beamline and spectrometer for inelastic soft X-ray scattering at high resolution in a highly efficient system are presented. Based on the energy-compensation principle of grating dispersion, the design of the monochromator-spectrometer system greatly enhances the efficiency of measurement of inelastic soft X-rays scattering. Comprising two bendable gratings, the set-up effectively diminishes the defocus and coma aberrations. At commissioning, this system showed results of spin-flip, d-d and charge-transfer excitations of NiO. These results are consistent with published results but exhibit improved spectral resolution and increased efficiency of measurement. The best energy resolution of the set-up in terms of full width at half-maximum is 108 meV at an incident photon energy tuned about the Ni L3-edge.
    Journal of Synchrotron Radiation 03/2014; 21(Pt 2):325-32. · 2.19 Impact Factor
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    ABSTRACT: Upgrading the long trace profiler at NSRRC has enabled measurements on mirrors in the beamlines with increased precision. The following working items are included: a 2D CCD detector and its upgraded software, improved straightness of the sliding stage of air bearings, calibration of the system linearity, control of air turbulence in the optical path and some upgraded optics. The factors influencing the stability and accuracy were studied and improved with engineering schemes. Measurements of highly precise flat mirrors and strongly curved mirrors were performed and are discussed.
    Journal of Physics Conference Series 03/2013; 425(21):212006.
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    ABSTRACT: The X-ray Nanoprobe (XNP) Beamline Project has been granted as one of the first seven beamlines at the Taiwan Photon Source (TPS). The XNP beamline and the associated instruments are designed to utilize the highly brilliant TPS light source for resolving the atomic, chemical and electronic structures of semiconductor-based devices with tens nm spatial resolution in tomographic and nondestructive manners. The beamline optics is deliberated to deliver focal spot around 40 nm with photon flux in the level of 1010 photons/sec. The stability of the focal position will be highly improved by operating the double crystal monochromator (DCM) in horizontally diffracting geometry, with minor sacrifice in energy resolution. The relative movement between sample and focusing optics is controlled by ultra-precise linear translational/flexure stages and monitored by laser interferometers. The end stations will provide conventional X-ray probes including, X-ray fluorescence (XRF), X-ray absorption fine structures (XAFS), X-ray excited optical luminescence (XEOL), and the emerging techniques, such as the Bragg-ptychography (BP) to overcome the spatial resolution set by the focusing optics. A novel scanning mechanism incorporating surface diffraction and BP for mapping the 3D interfacial strains is under development. The XNP beamline and associated instruments are expected to take the first synchrotron light by the end of 2015.
    Journal of Physics Conference Series 03/2013; 425(18):182005.
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    D J Wang, C C Chiu, C M Cheng
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    ABSTRACT: We have designed and constructed several manipulators for cryogenic samples and soft X-ray and VUV spectra. These manipulators are compatible with ultrahigh vacuum and up to six axis motions – three translational and three angular motions. Three translational and the polar angular motions are implemented with commercial stages. The azimuthal (in the beam direction) and tilting motions are driven with separate gear trains and connected to stepping motors on the top flange (100 CF). The azimuthal angular range is about ±180°, and the tilting range is from 75° to −25°; the resolution is better than 0.1°. The sample position is designed to be situated at the center of the polar and azimuthal rotation axes. The tilting axis is designed with an offset to decrease the spatial interference with the analyzer for photoemission spectra. The sample is attached to the sample holder and transferred to the cryogenic stage via a load-lock system. The sample holder is cooled with a continuous-flow cryostat (Janis ST-400) via flexible copper braids. With liquids helium and nitrogen for the cryostat, the lowest temperature of the sample holder attains 9.15 K and 82.4 K, respectively. During tests, the rate of consumption of liquid helium is less than 0.8 L/h.
    Journal of Physics Conference Series 03/2013; 425(12):122007.
  • D.-J. Wang, C.-C. Chiu, C.-M. Cheng
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    ABSTRACT: 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.
    Diamond Light Source Proceedings. 10/2011; 1(MEDSI-6).
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    ABSTRACT: Taiwan photon source (TPS) project has been proposed 3 years ago to create a 3 GeV synchrotron light source. The designated ultra-low emittance of this new light source requires high precision positioning of storage ring magnets. Among all the magnets, the alignment of quadrupole magnets is of most importance since it directly affects the closed orbit of electron beams. Conventional on-site alignment of quadrupole magnets was mainly relying on the theodolite performance. The cumulated errors could be in the order of 0.1 mm. In this report, a new alignment scheme is proposed to enhance the on-site alignment of quadrupole magnets for TPS project. To achieve the high precision requirements, a device possessing the advantages of both vibrating wire method (VWM) and position sensing detector (PSD) is proposed. The development of this alignment device is anticipated to provide a better mechanism to properly align the quadrupole magnetic centres on girder with less than 20 mum positioning errors.
    Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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    ABSTRACT: The Taiwan light source (TLS) uses a photon beam intensity system (Io monitor) to index the electron beam stability. This index combines the information of the fluctuations of electron beam position and size. For understanding the impact of these fluctuations to the electron beam instability, a set of the optical diagnostic system was installed in the TLS BL10 diagnostics beamline. This system includes the photon beam position monitor (PBPM), the beam size monitor (BSM) and the Io monitor. From the result, we concluded that about one‐third impact of beam instability came from the fluctuation of electron beam position and about two‐thirds impact of beam instability came from the fluctuation of electron beam size. The hardware configuration is described in this paper. © 2007 American Institute of Physics
    AIP Conference Proceedings. 01/2007; 879(1):702-705.
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    ABSTRACT: To accommodate the growing number of users in the soft X-ray spectroscopy research at NSRRC, we have developed a modified Dragon-type beamline, namely the active grating monochromator (AGM) beamline. In this beamline, a selected photon beam of 9 mrad radiation fan in the horizontal direction from a bending magnet is focused horizontally by a tangential elliptical mirror to a position 1.7 m after exit slit, and vertically by a cylindrical vertical focusing mirror (VFM) onto the entrance slit. After the entrance slit, the photon beam is energy-dispersed and vertically focused by an active grating onto the fixed exit slit. During the energy scan, the radius and shape of the active grating are adjusted accordingly, and therefore the defocus and coma aberrations terms can be effectively eliminated, and hence the energy resolution is optimized. Following the exit slit, the dispersed photon beam is refocused by a toroidal mirror onto the sample. Shadow ray-tracing program is employed to simulate the beamline performance. Results show that the energy resolution can reach 10000, 6000, and 3500 in the energy ranges of 300–400 eV, 400–600 eV, and above 600 eV, respectively. The total photon flux at sample position should reach 1×1012 phs/sec/200mA/0.1%BW, and the focused beam size at sample position is estimated to be 1 mm × 0.2 mm (H × V, FWHM). This beamline is currently under construction and will be ready for commission in December, 2006.
    01/2007;
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    ABSTRACT: During the last two years, a series of beam parameters measurement, subsystem checkout, installation of various sensors, control program modification and hardware upgrade made the top-up injection possible in practical routine operation. Top-up injection is an operation mode in which the beam current in the storage ring is maintained above certain level by frequent injections. The routine current stability is in the range of 10-3 for long period of operation. The Top-up injection provides advantages in operation such as lower emittance, higher current, smaller coupling, smaller ID gaps, exotic bunch filling patterns, and higher bunch charge. It also provides constant thermal loading on all components in the storage ring and the optics components of beamlines, as well as constant signal to the beam position monitor. Discussions on the results of some measurements of booster and storage ring, the requirement of hardware upgrade and the summary of routine Top-up operation will be presented in this paper.
    12/2006; 879:13-16.
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    ABSTRACT: For the future TPS project in the NSRRC, ground vibration would be important for this new machine. We have monitored the ground vibration under various experimental conditions at NSRRC site. Sensors were installed in different sites, on the ground and underground in different depth up to 40 meters. From the collected data, we compare the effect of day and night, traffic effect, and internal machine vibration. Specific vibration sources and their propagations are also discussed.
    01/2006;
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    ABSTRACT: A beam size monitor based on the synchrotron radiation interferometer (SRI) was installed in the NSRRC TLS. This monitor consists of a simple diagnostic beamline with a water-cooled beryllium mirror inside and a detecting optical system for both vertical and horizontal beam size measurement. The beam sizes measured are 47 micron and 160 micron respectively and are more close to the theoretical values than the synchrotron image monitor. Comparing with other monitors, at least 1 micron beam size variation is detectable. To minimize the thermal effect, the mirror is located far away from the source point and closed to the detecting optical system. The thermal distortion of the mirror is quite small measured by a portable long trace profiler (LTP) and agrees with the simulating analysis. The detailed monitor system design and testing results are presented in this paper.
    Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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    D.J. Wang, H.C. Ho, J. Wang, Z.D. Tsai
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    ABSTRACT: Water flow related vibrations were found on the spectrum of electron beam position monitor in the NSRRC. They were associated with the vibrations of quadrupole magnets. One major vibration source was from a pump in the cooling water system. Most amount of vibration coupled through water pipe and water flow and propagated to the magnets. A small water flow station was set up to study the effect about coupling, propagating and excitation. Some damping schemes tested in the ring to improve the vibration are also included.
    Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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    ABSTRACT: The Taiwan Light Source (TLS) is the first third-generation light source in Asia. The storage ring has six straight sections one section for injection, one for the RF cavities and diagnostic instrumentation and four sections for insertion devices, which are U5, U9, EPU and W20. Generating high-energy X-ray photons is a high priority at TLS. A single hybrid type wiggler is associated with three beam lines to serve X-ray users. The installed Superconducting Wavelength Shifter (SWLS) is very compact in size and can produce very high-energy photons. The injection section at TLS can barely accommodate the SWLS. The expected multipole components of the SWLS are strong, shrink the dynamic aperture; perturb the beta function, and reduce the beam lifetime. The increase in the synchrotron radiation by the SWLS also changes beam emittance and increases the energy spread. The influence of SWLS on the low-energy, 1.5GeV, storage-ring should not be neglected. The downstream kicker with the water-cooled copper mask must be modified to prevent a potential meltdown of the welding junction of the ceramic chamber because the heat load is high. The 1.2μs half-sine pulse field of the kicker is then altered by the copper-made radiation mask, which is installed inside the ceramic chamber. The operating capability of cryogenic system is established to ensure the smooth commissioning of the SWLS. The magnetic field mapping, the dynamic aperture simulation data and commissioning results will be presented and discussed herein.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2005; 550(1):446-453. · 1.14 Impact Factor
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    ABSTRACT: By using two aspherical variable-line-space active gratings and applying the energy compensation principle, we have designed a very efficient active grating monochromator — active grating spectrometer (AGM-AGS) beamline system for the photon demanding inelastic soft-x-ray scattering experiments. During the energy scan, the defocus and coma aberrations of the AGM can be completely eliminated to make the focal point fixed at the sample position and to maintain high spectral resolution for the entire spectral range. The AGS, which has an optical system identical to that of the AGM, but positioned reversely along the optical path, collects the photons emitted from the sample with a nearly identical energy spread as the AGM and focus them onto a position sensitive detector located at the exit slit position. The ray tracing results show that the efficiency of the AGM-AGS is two orders of magnitudes higher than that of conventional design while maintaining a very high spectral resolution.
    AIP Conference Proceedings. 05/2004; 705(1).
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    ABSTRACT: Two high-performance asymmetric-cut curved crystal monochromator (ACCM) side-branch x-ray beamlines have been designed to fully utilize the sideway output of a superconducting multipole wiggler (SMPW) source for protein crystallography research. Each of the two ACCM beamlines collects 1 mrad of radiation in the horizontal direction. One of them is located at 4 mrad and the other at 3 mrad away from the centerline of the radiation fan of the wiggler output. These two beamlines will deliver photon flux, through a 100 mum pinhole, of greater than 1×1011 photons/sec with energies from 12 keV to 14 keV and resolution (DeltaE/E) of 1.5×10-3 for standard monochromatic crystallography experiments. A Rh-coated, water-cooled vertical focusing mirror is placed upstream of the ACCM to simplify the energy tuning mechanism and to reduce the heat load of the crystal by cutting off the photon beams at energies above 15 keV. Considering that existing ACCM designs with bender either have insufficient cooling efficiency or are difficult to manufacture, we designed a special cost-effective ACCM that comprises a crystal plate affixed to a water-cooled, bendable Cu substrate, where heat conducts through a paste-like alloy. With this design, the monochromator will provide high photon flux and resolution while maintaining excellent stability.
    AIP Conference Proceedings. 05/2004; 705(1).
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    ABSTRACT: Crystal analyzers produced by spherically bending a Si crystal wafer are employed in high-resolution inelastic x-ray scattering experiments to increase the counting efficiency. The fabrication commonly involves dicing the crystal wafer into blocks of {approx}1mmx1mm to release the bending strain before gluing the wafer onto a spherical substrate. During the gluing, the relative alignment of each block must be maintained to achieve the desired focusing effect. A novel pressing tool has been designed to apply uniform pressure on the wafer during the gluing process to ensure the relative alignment between the crystal blocks, and has produced analyzers with satisfactory performance. The design details and the fabrication process will be presented and discussed.
    Synchrotron Radiation Instrumentation, 01/2004: pages 869-872;
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    ABSTRACT: A novel monolithic mechanical bender has been designed and fabricated to meet the requirements of an active polynomial grating in a new soft X-ray scattering and emission beamline at the National Synchrotron Radiation Research Center, Taiwan. This compact bender achieves nearly fixed center point under different bending conditions. Moreover, the compact bender can be bent to a desirable third-order polynomial surface profile to cancel the defocus and coma aberrations using two PZT actuators. Theoretical analysis reveals that the grating has unprecedented spectral resolving power. A detailed mechanical analysis has been conducted and a prototype bender was fabricated and tested. The results indicate that the performance of the bender is excellent and is therefore suitable to be used in the active grating.
    Journal of Synchrotron Radiation 12/2003; 10(Pt 6):450-4. · 2.19 Impact Factor
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    ABSTRACT: Emittance coupling between vertical and horizontal planes at TLS has been investigated. Using a set of skew quadrupoles, the coupling can be corrected to an acceptable value. The coupling sources are studied and possible errors are reduced.
    Particle Accelerator Conference, 2003. PAC 2003. Proceedings of the; 06/2003
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    ABSTRACT: In order to index the photon stability at Taiwan Light Source (TLS), an Automatic Peak Tracking System (APTS) of photon intensity has been established. The incident photons were focused by a vertical focusing mirror and detected by a photodiode, which is positioned behind a 50 µm pinhole. The position of pinhole detector is driven by an automatic peak-current detecting program with compensation of motor's backlash. The intensity fluctuation, long-term or short-term, is one of the major gauges of the beam stability. Correlation between the parameters of storage ring and measurement results will be presented.
    01/2002;
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    ABSTRACT: The thermally-induced deformation of the magnet girder has been observed to cause positional changes of the magnet and the beam position monitor (BPM) in the order of microns. This work investigates the deformation mechanisms. Methods for reducing the deformation are also proposed and applied in the storage ring. The mechanical stability of the girder reached ±0.1 µm per shift after improvement. Photon BPM and intensity monitor in the beamline were enclosed to compare the influence of the mechanical stability of the girder.
    01/2002;