Beam into the chamber

The next step is to get beam into the microscope chamber. Go to some relatively large beamline slit settings like 200/200/0 slits, for ENS_I=200 $\mu$m, EXS_I=200 $\mu$m, and EXSY_I wide open. Look in the upstream inboard viewport; you should see the snout as a long metal tube with a glass section in its middle (see Fig. 12.2). Inside this glass section is a mirror that lets you look down the direction of the beam path towards the exit window between the beamline vacuum and the inside of the STXM chamber. You should be able to see beam on the phosphor around the exit window, and adjust the chamber accordingly. Of course you have to have all valves and shutters in the beamline open, for seeing beam on the phosphor.

Figure 12.2: Picture of the STXM IV snout. The kinematic mount platforms for the zone plate and OSA are shown as mZP and mOSA, respectively. The glass cones on which they are mounted are shown as cZP and cOSA. The mirror on which you look to see the x-ray beam on the phosphor around the exit window is indicated with Mirror.

If the microscope is close to being aligned, you can simply monitor the flux on a detector to evaluate the alignment of the microscope chamber to the beam. If you are really starting from the beginning, you will need to remove the zone plate and OSA (see Sec. 12.2.4), and scan a 5-10 $\mu$m diameter pinhole as the sample to evaluate the illumination of the exit window. If the exit window is not illuminated homogenously, you will have to move the the whole STXM chamber by turning the manipulators which control the tripod it is sitting on. Do iterative steps of moving the chamber and scanning the pinhole over the exit window, until you are satisfied with its illumination. At the end of this iterative procedure, you should have reasonably even and bright illumination of the exit window.
In between scans you always need to make sure, you still get signal into the detector. You can even scan the detector in (XDET vs. YDET) and center it according to that scan. (You can make sure certain detectors - not the proportional counter though - are working by seeing if they respond to visible light leaking into the chamber). Whenever you change the alignment of the detector don't forget to record the new alignment.