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  • 1
    Electronic Resource
    Electronic Resource
    Smectic–smectic phase transitions in binary liquid-crystalline mixtures of DB5–T8 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3917-3929 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used high-resolution x-ray diffraction and ac calorimetry to study the liquid–crystalline smectic-A-smectic-A phase transitions in binary mixtures of polar mesogenic compounds DB5 [benzoic acid, (4-cyano)-4-[(4-pentylphenoxy) carbonyl] phenyl ester] and T8 [(E)-benzoic acid, 4-octyloxy-4-[2-(4-cyanophenyl) ethenyl] phenyl ester]. A detailed synthesis for each of these compounds is presented. The smectic A1 phase in this system shows two collinear diffuse x-ray maxima at incommensurate wave vectors, indicating a tendency to form the predicted Ai1 phase with two strongly coupled density modulations having incommensurate wavelengths. The Ad peak position, while both temperature and concentration dependent, is remarkably constant along the N–Ad phase boundary. In the vicinity of 16 mol % T8, both the x-ray and heat-capacity results are reproducibly history dependent. The simultaneous observation of sharp A2 and Ad peaks most likely results from phase coexistence, but a condensed incommensurate Ai2 phase cannot be ruled out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457798
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  • 2
    Electronic Resource
    Electronic Resource
    A finite element analysis of room-temperature silicon crystals for the advanced photon source bending-magnet and insertion-device beams (abstract)a) : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2064-2064 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this paper, the results of a series of thermal and distortion finite element analyses performed on room-temperature silicon for the three standard APS sources, namely, the bending magnet, wiggler A, and undulator A, are reported. The modeling was performed with the silicon cooled directly with water or liquid gallium through rectangular channels. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145728
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  • 3
    Electronic Resource
    Electronic Resource
    A finite element analysis of room-temperature silicon crystals for the advanced photon source bending-magnet and insertion-device beamsa) (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2713-2718 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this paper, the results of a series of thermal and distortion finite element analyses performed on room-temperature silicon for the three standard APS sources, namely, the bending magnet, wiggler A, and undulator A, are reported. The modeling was performed with the silicon cooled directly with water or liquid gallium through rectangular channels. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145615
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  • 4
    Electronic Resource
    Electronic Resource
    Counting statistics and loss corrections for the APS : Proceedings of the 4th international conference on synchrotron radiation instrumentation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 1225-1228 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: It has been suggested that for timing experiments, it might be advantageous to arrange the bunches in the storage ring in an asymmetrical mode. In this paper, we determine the counting losses from pulsed x-ray sources from basic probabilistic arguments and from Poisson statistics. In particular the impact on single-photon counting losses of a variety of possible filling modes for the Advanced Photon Source (APS) is examined. For bunches of equal current, a loss of 10% occurs whenever the count rate exceeds 21% of the bunch repetition rate. This changes slightly when bunches containing unequal numbers of particles are considered. The results are applied to several common detector/electronics systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143088
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  • 5
    Electronic Resource
    Electronic Resource
    A synchronized rotating crystal x-ray beam chopper (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 2852-2855 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new x-ray beam chopper has been designed and tested at the Advanced Photon Source. This beam chopper uses the diffractive properties of a rotating crystal to produce transmission window times as short as about 10 ns from a single diffracting face for 10 keV radiation. Precision control of the crystal rotation allows phase locking with the orbital frequency of the synchrotron storage ring; hence, the transmission of short x-ray pulses, corresponding to the 50 ps full width at half maximum charge bunch length, is possible with any fill pattern presently used at the Advanced Photon Source storage ring. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1485780
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  • 6
    Electronic Resource
    Electronic Resource
    A synchronized rotating crystal beam chopper (abstract) : Papers from the 12th National Synchrotron Radiation Instrumentation Conference (2002)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 73 (2002), S. 1545-1545 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A rotating crystal beam chopper that can be synchronized to the synchrotron storage ring frequency has been successfully fabricated and tested. The crystal chopper uses the storage ring frequency master clock as input and operates at 1/500 times its input frequency. It is phase locked to the input frequency. At the Advanced Photon Source, using the ring frequency clock (∼271 kHz), the crystal beam chopper rotates at about 542 Hz, with less than 3 ns jitter in the period. With its Si(111) reflecting surfaces, this corresponds to a transmission window of about 10 ns for 10 keV x rays, assuming the upstream monochromator is also Si(111). By dividing its input frequency, it is possible to operate the crystal chopper at 271 and 135.5 Hz for wider transmission windows. To date, this is the only device that has demonstrated a ns range transmission window and operates phase locked to the synchrotron storage ring frequency. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1448164
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  • 7
    Electronic Resource
    Electronic Resource
    Performance limits of direct cryogenically cooled silicon monochromators – experimental results at the APS (2000)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 7 (2000), S. 12-17 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The successful use of cryogenically cooled silicon monochromators at third-generation synchrotron facilities is well documented. At the Advanced Photon Source (APS) it has been shown that, at 100 mA operation with the standard APS undulator A, the cryogenically cooled silicon monochromator performs very well with minimal (〈2 arcsec) or no observable thermal distortions. However, to date there has not been any systematic experimental study on the performance limits of this approach. This paper presents experimental results on the performance limits of these directly cooled crystals. The results show that if the beam is limited to the size of the radiation central cone then, at the APS, the crystal will still perform well at twice the present 100 mA single 2.4 m-long 3.3 cm-period undulator heat load. However, the performance would degrade rapidly if a much larger incident white-beam size is utilized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049599014478
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  • 8
    Electronic Resource
    Electronic Resource
    Parametric down conversion of X-ray photons (2000)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 7 (2000), S. 81-88 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Parametric down conversion of X-ray photons in diamond crystals was detected in two experiments, both using the phase-matching scheme first employed in the X-ray regime by Eisenberger & McCall [Phys. Rev. Lett. (1971), 26, 684–688]. The conversion events were detected by a combination of time-correlation spectroscopy and energy discrimination, using Si drift-chamber detectors. The time-correlation spectra give a direct comparison of the conversion rate over the accidental coincidence rate. Mechanisms for possible detection of false events and ways to cross check against them are discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049599015113
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  • 9
    Electronic Resource
    Electronic Resource
    Performance limits of indirectly cryogenically cooled silicon monochromators – experimental results at the APS (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 22-25 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The results of high-heat-load tests of indirectly cryogenically cooled silicon monochromators are presented. The measurements show that, provided that the total power absorbed by the crystal is less than ∼150 W, indirect cryogenically cooled silicon monochromators will perform well, with thermal-induced slope errors of less than 2 arcsec. At the Advanced Photon Source, this corresponds to the undulator closed-gap (11 mm) condition at 100 mA with white-beam slit sizes slightly larger than the full width at half-maximum of the radiation central cones. The dependence of the slope errors on the thermomechanical properties of silicon are discussed and clearly demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049500013868
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  • 10
    Electronic Resource
    Electronic Resource
    Nonlinear thermal-distortion predictions of a silicon monochromator using the finite element method (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 1140-1148 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Silicon crystal monochromators at cryogenic temperatures have been used with great success at third-generation synchrotron radiation sources. At the Advanced Photon Source the unique characteristics of silicon at liquid nitrogen temperatures (80 K) have been leveraged to significantly reduce the thermally induced distortions on beamline monochromators. Finite element simulations of the nonlinear (temperature-dependent material properties) thermal stress problem were performed and compared with the experimental measurements. Several critical finite element modeling considerations are discussed for their role in accurately predicting the highly coupled thermal and structural response of the optical component's surface distortion to the high thermal heat flux. Once an understanding of the effects of (i) local element mesh size, (ii) area/surface heat flux versus volumetric heat generation, and (iii) uniform volumetric absorbed power versus a depth-dependent absorbed power, a final series of simulations was performed. Depending on the estimated convection heat-transfer coefficient, the final refined finite element model's predictions correlated well with the experimental measurements. In general, the use of the finite element method in predicting the overall thermal and structural behavior of the surface of the optical components with a high heat flux was shown to be quite effective.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0909049501012006
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