Impact of Pressure Regulation of Cryogenic Fluids and EPICS EPID Feedback on the Monochromatic Beam Position Stability of the 7ID Beamline at the Advanced Photon Source

The first crystal mount of the double-crystal Si (111) cryogenically cooled monochromator of the 7ID beamline at the Advanced Photon Source (APS) is slightly sensitive to pressure variations in the cryogenic lines. Pressure variations during a liquid nitrogen cryocooler fill every 4 hours move the beam by tens of microns. Pressure variations due to the cryocooler closed-loop pressure control with a heater element (around 0.3 psi) move the beam by 5 microns every 15 seconds. We have recently stabilized the coolant pressure with a simple pressure regulator that is in use at many beamlines of the APS. This paper shows the improvements in beam position stability made using this simple yet effective pressure-regulation circuit. We also recently added beam-position feedback to the second-crystal Bragg angle of the monochromator. The Experimental Physics and Industrial Control System (EPICS) Enhanced Proportional-Integral-Differential (EPID) feedback record implementation resulted in an additional improvement of the standard deviation of the beam position to 0.5 μm