The X-ray source of the CHX beamline is a 3m long in-vacuum undulator with 20 mm magnetic period, located in a low-beta straight section of the NSLS-II storage ring (IVU20)
The first optical element is a water-cooled horizontally deflecting flat mirror at fixed incidence angle (HDM). The cryo-cooled, pseudo-channel-cut Double Crystal Monochromator (DCM) provides a choice of Si111 or Si220 crystals in vertical scattering geometry. The crystals can be completely removed from the beam for operation with a wider band-pass monochromatic beam using the Double Multilayer Monochromator (DMM). The DMM houses two sets of substrates in horizontal reflection geometry, one set is coated with multilayers, while the other set provides bare and Rh coated Si stripes for use as a Harmonic Rejection Mirror (HRM) in monochromatic operation mode. It is also possible to remove both DMM and HRM completely from the beam (this is the most likely 'day 1' operating mode)
Vertical focusing of the X-ray beam in a x:y geometry is accomplished by water-cooled 1D compound refractive lenses. To achieve nearly achromatic focusing, different sets of lenses are available in a so-called Transfocator that also exhibits a large travel range along the beam direction. A safety shutter is located at the end of the FOE that allows keeping the high heat load synchrotron beam on the optical elements while entering the endstation.
The CHX endstation is equipped with two kinoform focusing units (KL1) and (KL2). Each unit hosts Si wafers with various lenses for different energies and the units provide a travel range along the beam direction to make the focusing more achromatic. For typical SAXS experiments, KL1 is used for horizontal focusing, whereas in WAXS experiments KL1 is used for vertical focusing and KL2 for horizontal focusing.
The CHX endstation provides a flexible instrument optimized for coherent X-ray scattering studies in SAXS or WAXS geometries, including the possibility of achieving grazing incidence (GI) on liquid samples for GI-SAXS/WAXS. This combination is of particular interest for studies of complex materials and understanding the interplay between structure and dynamics. The endstation features an optics table hosting several beam defining optics, a versatile diffractometer providing both horizontal and vertical scattering geometries and a SAXS table with adjustable flight tube length (up to 15 m).
Computer System Hardware & Software
Beamline control is achieved from EPICS via the "Control System Studio" (CSS) which is a set of graphic users interfaces allowing to control each instrument, or "ophyd", a python-based ("spec-like") command line interface for scanning. Data analysis is performed in python with tools provided for standard XPCS analysis