NECAT Beamline

The Northeastern Collaborative Access Team (NE-CAT) facility at the Advanced Photon Source at Argonne National Laboratory is managed by Cornell University and consists of seven member institutions:

  • Columbia University
  • Cornell University
  • Harvard University
  • Memorial Sloan-Kettering Cancer Center
  • Massachusetts Institute of Technology
  • Rockefeller University
  • Yale University.

    • Primary funding for this project comes from the National Center for Research Resources (NCRR), a division of the National Institutes of Health (NIH). Additional financial support for NE-CAT comes from the member institutions.

    Status of NE-CAT Sector 24 Activities

     

    January 2007  

     

    The APS accelerator operation was shut down for nearly the entire month of January for scheduled maintenance. Therefore, there is no NE-CAT or APS General User experience to report for the month of January. Resumption of user operations is scheduled for January 30.

    During this shutdown period, NE-CAT’s staff effort was directed to the development and implementation of several new beam line capabilities as described by the following.

    24-ID Phase 1 Beam Line User Operations

    New software has been developed and successfully tested to automatically change x-ray energies over a wide range and maintain the beam on the sample.

    A new utility package has been added to aid experimenters. This utility consists of a number of user aids, including: 1) an “Exposure Time Calculator” which provides users with an estimate of the data acquisition time appropriate to accumulate the needed data statistics, 2) a “Disk Space Calculator” providing an estimate of how much disk space is required to store a complete data set, 3) an “Energy to Wavelength Converter”, 4) a “Wavelength to Energy Converter”, 5) a “Resolution Converter” which for a given distance between the sample and the detector face calculates the maximum possible resolution obtainable at the edge of the detector, and 6) an “Attenuation Calculator” providing the percent transmission through a given set of attenuators at a given energy.

     

    24-ID Phase 2 Fixed-Energy Beam Line Installation and Commissioning

    Early in January, Oxford-Danfysik engineers arrive to correct the design deficiencies in the Phase 2 monochromator , which was only partially successful. The defective nano-motor drives for the Bragg angle motion of the crystal cage were replaced by servo-motors. The following photograph shows the motors located on a new back panel of the crystal cage.

     

     

    Installation of these new servo-motors has now corrected the earlier observed problem with non-reproducible motion of the Bragg angle.

    A replacement pico-motor was installed for the Si 311 crystal (providing x-rays at 14.78 KeV), hoping that this would solve the problem of adjusting the alignment of this crystal when inserted into the beam line. However, two problems were uncovered during early testing of the Si 311 crystal. The first problem observed was a high-frequency vibration of the beam position in the horizontal direction. This was attributed to vibrations of the crystal introduced through vibrations in the flexible liquid-nitrogen tubing due to flow of liquid nitrogen. This problem should be eliminated by re-engineering the flexible tubing. The second problem encountered was loss of fine motion adjustments. The nano-drives could be driven in only one direction. Once the beam was lost, it could not be restored. This problem is most likely due either to a problem with the motor itself or the imbalance of the spring mountings to the crystal cooling block. Since primary usage of the Phase 2 beam line will be with the Si 220 crystal providing x-rays at 12.66 KeV, it was decided to continue commissioning with the Si 220 crystal and delay corrections to the Si 311 crystal operation until the APS spring shutdown.

    The Phase 2 monochromator, since its delivery, has always had a poor vacuum- acceptable for commissioning but not acceptable for long-term operation. One problem noted early was that the glands of the liquid nitrogen supply lines connecting to the crystal cooling blocks were scratched in initial assembly by Oxford-Danfysik. The vacuum pressure was partially improved by wrapping the copper seals with indium metal to provide a tighter seal. However, under further testing it was noted that the cooling tubings brazed to the crystal copper cooling blocks were leaking. Oxford-Danfysik accepted responsibility for the poor workmanship and agreed to provide new cooling blocks prior to the APS spring shutdown for replacement. In order to continue commissioning of the Phase 2 beam line, the brazing leaks were temporarily sealed using a high-vacuum polymer material. With these fixes, the monochromator can continue to operate satisfactorily at a pressure of 3x10(-8) Torr.

    Micro-Diffractometer

    Assembly of the elaborate support stand for the MD2 micro-diffractometer is underway. This support structure has been designed to provide all the degrees of motion needed to rapidly and precisely align the MD2 to the x-ray beam. A design drawing of the table is shown below.

     

    APS Cross- Cut Review.

    n January 24, all APS macro-molecular CAT’s participated in a “structural biology cross cut review”. The purpose of this review was to assess the current status of the CAT’s and to make recommendations to Murray Gibson, Associate Laboratory Director for User Facilities, as to improvements that could be made. This review consisted of all the CAT representatives making presentations and well as participating in poster sessions before the APS Scientific Advisory Committee and invited experts in the field. At this time, the summary report of the review committee is not available.

     

     

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