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  • A number of improvements have been made to the Stainless Steel Seya beamline. The most significant change is the addition of new refocus optics to produce a smaller final image which is located further from the beamline exit flange. This improvement matches the Seya beamline to modern angle resolved photoemission experiments.

    The previous Seya exit mirror produced a final image only 222 mm (8.75 inches) beyond the exit valve flange. For many experiments, this was not enough clearance to center the chamber on the focused image. The former cylindrical exit mirror has been replaced by two mirrors that provide a smaller focused image at a much larger distance from the beamline exit flange. The new mirror system, designed by Sherry Crossley of the SRC optics group, was based on one existing mirror and one new mirror purchased from Acton Research Corporation of Acton, Massachusetts. The vacuum chambers and mirror holders were designed by Greg Rogers (SRC engineering) and built in the SRC and PSL shops. The new mirrors were installed November of 1993, and the mirror alignment was fine-tuned in May. The final image is now located 835 mm (33 inches) beyond the beamline exit flange, allowing even large experimental chambers to be centered on the focused image. The focused image now measures 1.5 mm wide by .9 mm high, compared to the former image size of 3 mm by 1 mm.

    New filter and diode arrays were also added to the beamline in November. Lithium fluoride and aluminum filters can now be easily inserted and removed from the beam path. A nickel mesh and gallium-arsenide-phosphide photodiode are available for monitoring the beamline throughput.

    The old manually-operated exit valve has been replaced by a pneumatic valve which can be interlocked to protect the beamline pressure during gas-phase experiments.

    Another improvement is the addition of a computer control system to the beamline which simplifies taking I-zero scans, and allows the user to enter any desired wavelength position and scan to it easily. The computer will automatically remove the backlash when scanning down in wavelength, and limit switches prevent scanning beyond the range of the instrument.

    Significant changes have also been made in the monochromator drive system. The former stepping motor has been replaced with a new micro stepping motor which allows finer control of the grating scan. The rotary encoder has been relocated to a more protected location inside the monochromator housing. Calibrations with the gas cell before and after the beamline relocation confirm that the scan is linear and accurate to within 1.2% throughout the scan range. The measured error in energy is not greater than 0.01 eV at 11.62 eV.

    The beamline relocation and the installation of the new exit optics were completed in 1993 by Mike Lagergren, Dan Wallace, and Sherry Crossley, all of the SRC optics group, and Greg Rogers, SRC engineering.