Patent Publication Number: US-7712960-B2

Title: Device for optimization of experimental parameters on synchrotron beam lines

Description:
This application claims the benefit of U.S. Provisional Application No. 61/031,416 filed on Feb. 26, 2008. 
    
    
     CONTRACTUAL ORIGIN OF THE INVENTION 
     The United States Government has rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the United States Government and The University of Chicago and/or pursuant to Contract No. DE-AC02-06CH11357 between the United States Government and UChicago Argonne, LLC representing Argonne National Laboratory. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a tool used for optimization of experimental parameters on synchrotron beam lines. 
     More specifically, this invention relates to a device having capability for implementing multiple procedures for the accurate alignment and calibration of multiple components of an experimental set up at a synchrotron beam line. 
     DESCRIPTION OF THE RELATED ART 
     On synchrotron beam lines there are a number of procedures that need to be performed in order to optimize experiments in general and data collection from macromolecular crystals in particular. 
     These procedures include: 
     1) Alignment of the sample rotation axis, 
     2) Visualization of the x-ray beam at the sample position for inspection of its quality and/or location, 
     3) Alignment of the x-ray beam with the sample position, 
     4) Proper calibration of the sample-to-detector distance especially for samples with large unit cells, 
     5) Proper calibration of the monochromator energy for experiments utilizing resonance effects near absorption edges, 
     6) Knowing precise coordinates of the direct beam (i.e. diffraction origin), especially for samples with large unit cells, and 
     7) Accurate centering of the beamstop. 
     Performing all or some of the above listed steps regularly would be beneficial for optimizing the experiment, which in turn would enhance the data quality, throughput and efficiency of a beamline. Usually, these steps are performed with separate tools, each of which has a single function. For example, there are alignment pins, x-ray visualization pins with a YAG crystal or a fluorescent “phosphor” on them, special mounts with metal foils for monochromator calibration, and the like. 
     Currently carrying out such optimization steps is arduous and time consuming, utilizing one alignment tool at a time. Because of this, some of the steps are often overlooked to save time and effort. For example, sample to detector distance calibration, beamstop centering and other useful steps may not be performed at all, or performed poorly. Some of the steps, for example, finding the diffraction origin, are performed with inferior and some times dangerous methods, which may damage expensive detectors, such as recording attenuated beam directly on the detector and finding the center of the recorded spot. 
     Principal objects of the present invention are to provide improved methods and a device enabling a plurality of procedures for implementing accurate alignment calibration of multiple components of the experimental set up at a synchrotron beam line. 
     Important aspects of the present invention are to provide such methods and device substantially without negative effect and that overcome some of the disadvantages of prior art arrangements. 
     SUMMARY OF THE INVENTION 
     In brief, enhanced methods and a device enabling a plurality of tools for implementing a plurality of procedures for the accurate alignment and calibration of multiple components of the experimental set up at a synchrotron beam line are provided. The device includes an alignment pin or needle for centering a sample rotation axis. The device includes a Yttrium Aluminum Garnet (YAG) crystal for visualization of the beam and beam alignment. The device includes a metal foil or foils for transmission or fluorescence measurements used for the monochromator calibration. The device includes a metal foil, a polymer or a powder for sample-to-detector distance calibration for finding the direct beam position and for centering the beamstop with powder diffraction. The device also includes provisions enabling further expansion of functionality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention together with the above and other objects and advantages may best be understood from the following detailed description of the preferred embodiments of the invention illustrated in the drawings, wherein: 
         FIG. 1  is a front plan view of an exemplary device or versatile pin having capability for implementing multiple procedures for the accurate alignment and calibration of multiple components of the experimental set up at a synchrotron beam line in accordance with the preferred embodiment; 
         FIG. 2  is a side plan view of the exemplary device of  FIG. 1  in accordance with the preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with features of the invention, a device or versatile pin is provided that is called a “VersaPin”. The device or VersaPin combines each of the tools needed to perform the above-listed optimization steps. The device or VersaPin of the invention carries an alignment needle for centering a rotation axis; YAG crystal for visualization of the beam and its alignment; metal foils to produce a powder diffraction pattern which will be used for finding the exact position of the direct beam, for calibration of the detector distance and for centering the beamstop. The device also carries metal foil or foils for calibration of the monochromator. Since all needed tools are assembled on a rigid post with known dimensions, one-time alignment of one of them is sufficient for putting any other tool in the position by simply applying the pre-determined offsets. The assembly of the device or VersaPin is based on commercially available pins used for crystal mounting and is compatible with all beamlines handling such samples. 
     Having reference now to the drawings, in  FIGS. 1 and 2  there is shown an exemplary device having capability for implementing multiple procedures for the accurate alignment and calibration of multiple components of the experimental set up at a synchrotron beam line generally designated by the reference character  100  in accordance with the preferred embodiment. 
     Device  100  includes an alignment pin  102  for centering a sample rotation axis with a sample needle  104  disposed at an upper end of the device  100 . Device  100  includes a YAG crystal  106  for visualization of the beam and its alignment and a metal foil  108  for transmission or fluorescence measurements used for the monochromator calibration; the same foil  108  can be used to produce powder rings for determining the exact direct beam position, for centering the beamstop and for calibrating the sample-to-detector distance. Device  100  includes a plurality of apertures or holes  110 ,  112 , for example, respectively used for different extent of functionality with the YAG crystal  106 , foils and, powders  108 , as shown, and the like. Device  100  may include up to four holes similar to  110  and  112  for expanded functionality. For example, it may be equipped with a PIN diode (not shown) for intensity measurements and scanning. 
     All holes, for example holes  110 ,  112 , are centered in slots  122  which are machined out from the post  120 . This provides protection for the YAG crystal, foils, powders and polymers from mechanical damage by preventing accidental contact with them. 
     Device  100  includes a base  114 , a spacer portion  116  disposed above the base  114 , and a tapered portion  118  disposed above the spacer portion  116 . The device  100  includes a post or member  120  supported by a tapered portion  118 . Post  120  includes a plurality of slots  122 . 
     The base  114 , spacer portion  116 , and tapered portion  118  may be formed as an integral unit, formed, for example, of a stainless steel material. The elongated member  120  is an integral member or rigid post mounted onto the tapered portion  116 . All slots  122  and holes  110 ,  112  are machined with known dimensions. All needed tool features  102 ,  106 ,  108  are assembled in the slots  122  on the rigid post  120  with known dimensions, as a result, a one-time alignment of one of the tool features  102 ,  106 ,  108  is sufficient to allow the other tool features to be moved to the required position by simply applying the pre-determined offsets. The assembly defining the device  100  is based upon commercially available pins used for crystal mounting and is therefore compatible with all beamlines handling such samples, and is compatible for use with commercially available sample exchanger robotics. 
     In accordance with features of the invention, a plurality of new functions of the device  100  is provided to accomplish several tasks on synchrotron beamlines primarily. However, it should be understood that some of the functionality of device  100  can be used, for example, on experimental stations based on in-lab X-ray generators. This device  100 , named VersaPin by the inventors, advantageously is made by modifying a commercially available, standard pin, for example, manufactured and sold by Hampton Research, or can be made from individually formed components and assembled together. 
     The device  100  or VersaPin advantageously is used for the following: 
     1. Centering the rotation axis on sample position 
     2. Visualizing of the X-ray beam for quick inspection of its quality 
     3. Alignment of the X-ray beam with the sample position 
     4. Obtaining the precise coordinates of the direct beam 
     5. Centering the beamstop on the direct beam 
     6. Calibrating the distance between the sample and the detector 
     7. Calibrating the monochromator at one or more energies 
     The device  100  or VersaPin replaces at least four different prior art tools including: alignment pin; beam visualization mount (YAG, phosphor screen, scintillator and the like); mounted foils for transmission or fluorescence measurements used for the monochromator calibration; and another separate mount for obtaining powder rings. 
     In accordance with features of the invention, the device  100  or VersaPin only requires initial centering of the needle  102 , which can be manual or automated. Then placement of all other positions is by simple translations by predetermined amounts, known from the specifications of the device  100  or VersaPin. Consequently, the device  100  or VersaPin enables a considerable savings of time. 
     In accordance with features of the invention, with the device  100  or VersaPin using powder diffraction for calibrating the detector distance and for finding the diffraction origin is much faster and more accurate than using other, more typically used methods, such as physical measurements of the distance, recording direct beam image and determining its center, using Bragg diffraction pattern from known crystal and the like.
         In accordance with features of the invention, and probably most importantly, with the device  100  or VersaPin all alignments and calibrations described above can be automated relatively easily, due to the fact that the single, rigid device  100  is used for these steps. Such automation is being implemented on beamlines at Argonne National Laboratory and the procedures below are specific for this site.       

     Procedures for GM/CA Beamlines 
     Mount and Align the VersaPin
         Mount device  100  on the goniometer head with omega=0°.   Drive the goniometer support outboard until the first slot  122  is roughly centered at the sample position, within the crosshairs of the high-resolution sample visualization camera.   Rotate device  100  on the magnetic base until YAG  106  is upstream or on the high resolution camera side, and is vertical; the low-resolution camera sees it “edge-on”.       

     Align the Rotation Axis
         Move the VersaPin inboard with the goniometer support horizontal motion until the needle is visible in the field of view of the high-resolution camera.   With “point-and-click”, center the needle.   Increase the high-resolution camera zoom to maximum and center the needle.   Align the rotation axis by combining the goniometer support vertical and point-and-click motions, as needed.   Return omega to 0.       

     Visualize and Align the Beam
         Move goniometer support horizontal 10 mm outboard.   Move the Crystal XY head X+1.03 mm.   Move Crystal XY Y+0.1 mm.   Search and close the hutch.   Open D shutter (B shutter on IDB line) and timing shutter.   Adjust the attenuation as needed.   Align the beam position as needed.       

     Direct Beam Coordinates, Beamstop and Sample-to-Detector Distance
         Close the timing shutter and move goniometer support horizontal+3 mm to position the foil  108 .   Record a diffraction image with 100× attenuation, 1 second exposure and 0.1° rotation width.   Match the movable circle in the MAR display software to the powder diffraction ring. The center of the ring is the center of direct beam.   Center the beamstop shadow on the center of the powder diffraction rings by iteratively moving the beamstop in the required direction or directions and taking diffraction images until the beamstop is centered.   Click anywhere on the first, lowest resolution, diffraction ring and write out the pixel address X and Y in mm.   Calculate D=SQRT((Xr−Xb)2+(Yr−Yb)2)/(Tan(2 arcsin(λ/2d)))+1.875 mm; where D is the sample-to-detector distance, Xr and Yr are the X and Y coordinates of any pixel in the ring, Xb and Yb are the X and Y coordinates of the direct beam (center of the diffraction rings), λ is the wavelength of the incident beam and d is the resolution or d-spacing (known) of the ring. The number 1.875 in this case is the distance from the position when YAG  106  is in focus to the foil  108 . The resulting number is the true distance between the sample and the detector.   For more accurate measurement of the distance, multiple points can be chosen on the powder ring and the results averaged.       

     Monochromator Calibration
         Start the monochromator calibration script.   If calibration at an additional energy is needed, move the goniometer support horizontal+3 mm to expose the additional foil (not shown) and start the calibration script.       

     The device  100  or VersaPin can be applied at various facilities, which differ by the range of their operational parameters such as the sample-to-detector distance, monochromator energy range, maximum beam intensity and the like. Facilities can also differ by functionality, for example, a fixed wavelength beamline. By choosing appropriate foils and powders device  100  or VersaPin can be designed to cover the widest range and most functionality of modern experimental stations (“one size fits all” approach). Alternatively, several types of devices  100  or VersaPins can be designed to address different ranges and functionalities separately (tailored approach), which can decrease the cost of the individual device. 
     While the present invention has been described with reference to the details of the embodiments of the invention shown in the drawing, these details are not intended to limit the scope of the invention as claimed in the appended claims.