The low-Z XAS hutch configuration consists of two separate Helium gas spaces. The front end / I0 section is supplied by SSRL house helium supply, while the low-Z sample box section is supplied by the Helium cylinder in the hallway behind the 4-3 blue electronics racks. The two sections are separated by a thin polypropylene film inside a clamped O-ring assembly as indicated in the picture.
The spaces are kept separate to speed up sample changing and Helium purge times. The polypropylene film will be damaged by the beam over a duration of 1-2 days. If a hole is formed in the film, the two spaces are no longer separate. This means that when a sample is changed, air is introduced into both the low-Z sample box AND the front end / I0 section. Air in the front end section can significantly change the I0 signal, as well as reduce the number of X-rays which reach your sample. This needs to be remedied by changing the polypropylene window.
To test for a leak between sections:
Remove one of the two paddles from the low-Z sample box and observe the flowmeter on the front/end I0 section. If the flow drops to zero, then there is a leak between the two sections, and you will need to change the polypropylene film.
To replace the polypropylene film and fix the leak between sections:
Move VERT and HORZ stage motors to reposition the low-Z sample box until the bellows is not bent vertically or horizontally. VERT is about 42, and HORZ is about 25, but check by eye and adjust if still bent.
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Test that the two gas sections are separated again. To do this, check that the He flowmeter is at a high value (it reads "H +F" above 500) and decreasing. The initial high value is because there is heavier gas (air) being purged out of the Front end / I0 section. It should eventually settle around 200-240 when only Helium is in the front end / I0 section. If the flowmeter value is already lower than this after clamping, this means there is a hole in the film. This often happens because the O-ring can cut the film. No worries! Just unclamp the assembly, replace the film, clamp and test again!
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