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  • 1994 User's Group Meeting -- A Look At The PGM

    A highlight of the annual SRC User’s Group meeting was the demonstration of a working prototype of the new Plane Grating Monochromator (PGM) design, which will be used with the 7-250 eV undulator, scheduled for delivery in January 1995.

    The PGM has some unique design elements, that have not been used before in a synchrotron beamline. The central concept behind the PGM is a mechanical coupling of the relative translation and rotation between the mirror and the grating. This means that the diffraction angle changes as the wavelength is scanned. By making the grating translate and rotate, rather than the mirror as in previous designs, the mirror mechanism becomes much simpler. This is important, since the mirror intercepts a high power density from the undulator, and must therefore be water cooled.

    Attendees at the User’s Group meeting were treated to a demonstration of the unusual mechanical design of the PGM by Mike Fisher of the Engineering Group. The bench tests of the prototype use a Zygo interferometer, which can characterize the mechanical precision of the motions of grating and mirror. It is also used to evaluate the interferometric feedback system that will be used to maintain monochromator accuracy during scanning.

    Aladdin -- Editor Brian Tonner