The hydrogen outgassing rate measured is 75% of that measured in 2000. The atmospheric accumulation is about 6.9 x 10^-8 torr liters/sec and seems high relative to that in y1 and the accumulations made at LLO. The value suggests a small leak. If this is in the beamtube it is at the threshold of not being able to be found with our current techniques. The results of the accumulation were more difficult to calculate and have more uncertainty due to the method of connecting the RGA to the beamtube. The connection was made by a corrugated small diameter tube rather than a mount directly on the beamtube. The pumping speed of the tube and the pumping speed of the RGA as an ion pump need to be accounted for. The attached pdf file shows the influence of the connecting tube and presents the results.
Yep, this level of air leak would be challenging to locate by current techniques. It's probably small enough not to directly impact sensitivity, but it seems important to establish whether there's a degradation process at work, like LLO Y. We should consider a repeat accumulation, perhaps with three sampling points along the 2km module.
I estimate some 3000 cm^2 of viton in the large valves exposed to this volume. This may account for some of the air. Anyone know the outgassing rate of viton after 140,000 hours under vacuum?
We should probably reconfigure the RGA to eliminate local orings and the low conductance of the flex hose. Kyle and I felt we had nothing to loose by trying the quick and dirty method first. Practice makes better.
Correction on the surface of viton contained in the LN pumps and large gate valves.
There are 4 gate orings entirely in the vacuum (45 inch diam) and 2 gate orings 1/2 exposed at the closed gate valves(45inch).
There are 4 flange orings 1/2 exposed where the gate valves bolt to the ln pumps(45 inch diam)
There are 2 bonnet seal orings 1/2 exposed in the two gate valves open to the volume - each is 144 inch long.
Total surface area ~ 6970 cm^2
If the entire air leak is allocated to this we get an outgassing rate for the viton of 1e^-11 tl/sec/cm^2.