pull the beam pipe (the kapton window) in here push the entrance slider from Kapton-covered hole to the "diamond window" thing. (slider IN is to +X)
open up the slits
in mfxhome find the radio button behind DG1 (screen left) on Motors and Actuators row, labeled REF, move the laser in and out (a mirror goes into and out of position). the laser should be plugged in and on, but make sure you see it along the beam pipe viewports if you're having issues.
It might be slits too closed if you see it along the way, but not at the interaction region.
This large mm-sized beam approximates the beam path well through the chamber and detectors to DG3. use tape or white cards or laser cards to track the path.