A new ``Cowan type`` double-crystal monochromator, based on the boomerang design used at NSLS beamline X-24A, has been developed for beamline 9.3.1 at the ALS, a windowless UHV beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline X-A, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m)

Jones, G.

Karlin, B.A.

Lindle, D.W.

Perera, R.C.C.

Ryce, S.

Woicik, J.C.

Perera, R. C. C.

Lindle, D. W.

Karlin, B. A.

Woicik, J. C.

UNT Digital Library

LBL-36350 TP n in Lawrence Berkeley Laboratory e UNIVERSITY OF CALIFORNIA P Accelerator & Fusion Research Division Presented at the 5th International Conference on Synchrotron Radiation Instrumentation, Stony Brook, NY, July 18-22,1994 and to be published in the Proceedings Design and Performance of the ALS Double-CrystaI Monochromator G. Jones, S .  Ryce, D.W. Lindle, B.A. Karlin, J.C. Woicik, and R.C.C. Perera August 1994 Prepared for the U.S. Department of Energy under Contract Number DE-AC03-76SF00098 DISCLAIMER This document was pnprrcd IS an . c c ~ u n t  of work sponsored by tbc United Stam GO-L While rhis documat is Wcvcd D conrain comm in€-tion. nciIbcr Ibc United Sutcr Government nor any agency rhereof. nor Tbc Regcnu of tbc University of cllifanio nor any of their cmployau. nukes my wamn~y. cxprrsr or implied. or assumes any lcpl responsibility for fhc accuracy. complctcncrs. or uscfulocu of any informttion. apparatus. @W or pnxcss disdorcd or rcprrrcnts thu iu use would not infringe po'vrrrcly owncd rights. Reference k i n  to my specific wmmrcid pmlucs proccIs, or renice by iu Odc nurr na&mut; manuf.aurcr. or otbawisc docr oo( Dearrrrily constitute or imply iu eadorruocat. nxmmcndacion. or favoring by rh United Sam Gomnmwc or any agency mermf. a nK Regmu of Chc U n i d t y  of Wfomia The vicws and opinions of urlhon ucpnrscd hcnin do no( Dcasurily sulc a nflca dmsc of thc United S a m  G o v a n m t  or any agmcy tbamf. a 'Ihe Regents of rh Univurity of Glifornh. DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document. I LBL-36351 LSBL-23: UC-411 DESIGN AND PERFORMANCE OF THE ALS DOUBLE-CRYSTAL MONOCHROMATOR* G. Jones, S .  Ryce, D.W. Lindle, B.A. Karlin, J.C. Woicik, R.C.C. Perera Advanced Light Source Accelerator and Fusion Research Division Lawrence B erkele y Lab oratory University of California Berkeley, CA 94720, USA Paper submitted at the 5th International Conference on Synchrotron Radiation Instrumentation, Stony Brook, New York, July 18-22, 1994 'This work was supported by the Director, Office of Energy Research, Office of Basic Energy kiences, MateriaIs Sciences Division, of the US. Department of Energy, under Contract No. lE-AC03-76SF00098. MASTER DISTRIBUTION OF THIS DOCUMENT IS UNLIMITEQgj . Design and Performance of the ALS Double-Crystal Monochromator G. Jones*, S. Ryce*, D. W. Lindle*j#, B.A. Karlin+, J.C. Woicik@, and I R. C. C. Perera" *Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, CA 94720 #Department of Chemistry, University of Nevada, Las Vegas, Las Vegas, NV, 89154 +National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY 11973 @National Institute of Standard and Technology, Gaithersburg, MD 20899. Abstract A new "Cowan type"' double-crystal monochromator, based on the boomerang design used at NSLS beamline X-24A, has been developed for beamline 9.3.1 at the ALS, a windowless UHV beamline covering the 1-6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x- rays at NSLS beamline X-23A2, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m). This work is supported by U.S. DOE under Contract No. DE-ACO3-76SFOOO98. 1 Introduction Third-generation synchrotron-radiation sources provide a unique opportunity for advancements in x-ray spectroscopy of atoms, molecules, and solids, owing to the high brightness available.1 In order to take full advantage of this opportunity, a stable monochromatic x- ray beam is required, which in turn requires a high-precision mechanism for scanning photon energy with the monochromator. This challenge is exemplified in beamline 9.3.1 at the Advanced Light Source (ALS), a windowless beamline covering the 1-6 keV photon- energy range designed for use by the ALS x-ray atomic and molecular spectroscopy program. Bearnline 9.3.1 is designed to achieve the goals of high energy resolution and high flux as well as to preserve the high brightness of the ALS source radiation. Design details of this beamline are presented elsewhere.2 In order to maintain high brightness at a distant sample while scanning the photon energy, it is desirable to have the monochromator mechanism as precise as possible. For spectroscopy applications, in fact, it is best to operate the monochromator without the usual intensity feedback system to eliminate any possible intensity variations induced by the feedback circuit. In addition, even sinall feedback corrections can alter the path of the beam through the optical system of the beamline, leading to changes in image quality at the sample. This desire for feedback-free running necessitates the use of a mechanical linkage in the monochromator mechanism. In order to attain the high precision necessary, it also is desirable to have as simple a drive mechanism as possible. Hence, the boomerang design3.4 used at beamline X-24A at the National Synchrotron Light Source (NSLS), in which a single linear motion actuates scanning of the monochromator, was taken as a model. An added benefit of this design is that it readily accomodates operation at low photon energies [e.g., near 2 keV with Si(ll1) crystals]. Performance of the beamline X-24A monochromator mechanism has been documented.4 Photon-energy scanning is accomplished from outside vacuum by a single linear motion with 15 cm of total movement. One benchmark for measuring the perfonnance of this device is the degree of non-parallelism, in the dispersion plane, of the two monochromator crystals as a function of this linear motion. Measurements on the original mechanism before it was placed in beamline X-24A exhibited an error of approximately 2 arcsec/cm of linear travel. In practice, actual results were a little worse (4 arcsec/cm 2 of linear travel).5 Nevertheless, as far as we know, this is as good or better than other existing mechanisms. D.esign of .the A L S .  D,o.uble-Crys..tal Monochromator The basic design principles6 of the new and improved "Cowan type" monochromator are identical to the original design? but several significant enhancements have been introduced. The primary change is the removal of all bearings from the mechanism, particularly the crossed-roller bearings used in the original design. Movement of the crystal mounts along the boomerang arms as well as all other linear motions use dovetail slides made of aluminum/bronze sliding on bases made of 304 stainless steel, with both surfaces treated chemically with a vacuum-compatible lubricant. This combination of materials is known not to seize even in ultra-high vacuum, and the hardness of the materials permits high-precision repetitive motion. We believe that replacement of the crossed-roller bearings is the primary reason for improved performance of the new design relative to the original. Other design modifications include a significant reduction in -the number of parts and use of more robust components. Reduction in the number of parts was accomplished by eliminating the crossed-roller bearings, by eliminating unneeded adjustments in the mechanism? and by consolidating multiple pieces into integrally machined components wherever possible. Photograph of the assembled monochromator including the crystal mounts in the small angle configuration is shown in Fig.1. Robustness was achieved simply by making many parts heavier or larger or using ribs for added strength in some larger components. Ease of alignment also has been enhanced by liberal use of fiducial marks throughout the mechanism, its support base, and the monochromator vacuum chamber. Finally, all precision parts were machined using numerically controlled techniques with specially prepared and matched machine tools. This latter effort was necessary to guarantee precise mating of the dove-tail slides. Performance. of. the. Monochromator To test the precision of the monochromator while scanning, a bench- top approach was used. A two-axis auto-collimator was aligned (< 1 arcsec) with respect to a right-angle mirror. The monochromator, equipped with mirrors in place of the two crystals, was positioned 3 between the right-angle mirror and the auto-collimator with the axis of its linear motion parallel (10-20 arcmin) to the axis of the auto- collimator. As the monochromator is scanned, angular misalignments between the two mirrors riding on the merhanism, both parallel (theta) and perpendicular (chi) to the diffraction plane, can be measured using the auto-collimator. Results of this test illustrate that the desired precision in theta has been met. For example, over 15 cm of linear travel in the boomerang mechanism, the two crystals (mirrors) remain parallel to within 10 arcsec. This is at least 3 times better than the original design for the same amount of linear motion.415 In addition, the change in angle is smooth and monotonic over this range. Over the entire range of motion of the new boomerang (23 cm), performance degrades by a factor of 2. Additional adjustment and testing is underway to improve these results. Tests with x-ray synchrotron radiation were performed at beamline X-23A2 at the NSLS. Absorption spectra at the Cr and Ti K edges taken with the new mechanism are shown in Figs. 2-3. These results agree very well with standard spectra at these edges. Both measurements were taken with unfocused synchrotron radiation, thus only providing a test of theta alignment. Nevertheless, these spectra were recorded with the piezoelectric feedback system turned off, and the measured monochromatic flm varied by only 7-10% over the photon-energy ranges of the scans. Beamline 9.3.1 at the ALS is a windowless beamline, covering the 1-6 keV photon-energy range, designed to achieve the goals of high energy resolution, high flm, and preservation of the high brightness from third generation synchrotron radiation sources like the ALS. For atomic and molecular spectroscopy experiments, a stable monochromatic x-ray beam is required. Hence, the beamline has to be equipped with a suitable monochromator. A double-crystal monochromator based on the boomerang design used at NSLS Beamline X-24A has been developed for this beamline. The measured mechanical precision of this new "Cowan type" monochromator shows significant improvement over existing designs, without having to use intensity feedback available with piezoelectric devices. In tests with x-rays, this new mechanism provided monochromatic light with an intensity variation of as little as 7% over several hundred eV in photon energy near the Cr K edge without feedback. We are confident 4 that this monochromator will provide a bright, high resolution, and stable x-ray beam for use in x-ray spectroscopy at the ALS. Acknowledgments This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. We would like to thank P.L. Cowan for his help and encouragement in development of this monochromator and W. Ng for assistance in testing the monochromator. Tests with x-ray synchrotron radiation were performed at NSLS, which is supported by the U.S. Department of Energy under Contract No. DE-AC020-76CH00016. Figure Captions Fig. 1 Photographs of the assembled unit, including the crystal mounts in the small and large angle configurations. Fig. 2 Chromium K absorption spectrum measured without using an intensity feedback system. Fig. 3 Titanium K absorption spectrum measured without using an intensity feedback system. 5 References: 1. B. Crasemann and F. Wuilleumier, Physics T,o.day, June 1984; D.L. Ederer, T. A. Callcott and R.C.C. Perera, Synchrotron Radiation News 7, 29 (1994). 2. R. C. C. Perera, G. Jones and D. W. Lindle, Rev. Sci. Ins-. ( In press). 3. J.A. Golovchenko, R.A. Levesque and P.L Cowan, Rev. Sci. Instr. 52 , 4. P.L. Cowan, J.B. Hastings, T. Jach, and J.P. Kirkland, Nucl. htr. and Meth. 208,349 (1983). 5. P.L. Cowan ( Private communication). 6. A right-angle linkage system (references 3 and 4) was used to avoid the difficulties of independently manipulating the six degrees of freedom for two crystals in vacuum while maintaining the crystals Bragg planes parallel (within a rocking curve width) to each other, as the monochromator is scanned. This is necessary to provide a spatially constant and high throughput beam throughout the full energy range. 509 (1981.). 6 d :I ................... e0 I i I I  ................. < ................... 5 ............. 1111 i .......... ..................... ........... 1 1 1 1  I l l 1  co Lo d- m (N T 0 0 0 0 0 (3 0 0 Lo co T- Lo 0 co T 0 c o >  o a  co m 0 co T 0 b 0.3 m S 0 Q 0 cn a a Y E .I CI L 3 S a I- .I .cI .I . . .  ............. ........................ 5 . ............ ............ - ..........................  cv 03 CD d- 7 T- 7 cv T- 1 1 1  ........................ 1 T- O 0 m I 0 (0 0 m 0 cv 0 m 0 03 a d- 0 d- a d- 0 0 a d- a3 0 

Design and performance of the ALS double-crystal monochromator

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Design and Performance of the ALS Double-Crystal Monochromator

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Design and Performance of the ALS Double-Crystal Monochromator

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