kyle.ryan@LIGO.ORG - posted 19:32, Friday 12 August 2016 - last comment - 14:06, Wednesday 24 August 2016(29079)
Y-end RGA captures IFO locking effects on partial pressures
After decoupling the pumping components used during the recent bake out of the Y-end RGA, I exposed the RGA to the Y-end vacuum volume, energized the filament and let it come into equilibrium for an hour or more. I then let the RGA scan continuously with the multiplier (SEM) on for an additional hour or so while I gathered up my mess(es). I periodically checked the scanning as I walked past the screen. At one point, I noticed that the spectrum was changing rapidly towards the "dirty". I monitored the scanning and noted that after reaching a temporary maximum, the amus which had increased then returned to near their original values. After consulting with the Jeff B. (the operator on shift), I feel that the observed changes in partial pressures were likely the result of IFO locking attempts as they coincide closely in time. Perhaps something gets hot when the IFO is locked or when mirrors are steered? See attached scans
Non-image files attached to this report
Comments related to this report
If true that could be kind of scary (!) Can we set an RGA in MID (stripchart) mode and run time series following the main peaks through a locking attempt?
I could imagine baking the adsorbed water off the ETM and perhaps nearby baffles. But this should not persist (or repeat) after the first good cavity buildup.
It's not clear whether this effect could be seen on the overall vacuum pressure, but if it could be, we don't see it. Here is 8 hours (yesterday/today) ofthe y-end vacuum pressure together with the y-arm transmitted power. I don’t see anything in the vacuum pressure channels that relates to the locking attempts, though that may be my untrained eye.
1. H1:ASC-Y_TR_A_NSUM_OUT_DQ, raw,start: 2016-08-13 00:00:00 (1155081617) len: 8:20:00.
2. H0:VAC-EY_Y3_PT410B_PRESS_TORR, raw,start: 2016-08-13 00:00:00 (1155081617) len: 8:20:00.
3. H0:VAC-EY_Y2_PT424B_PRESS_TORR, raw,start: 2016-08-13 00:00:00 (1155081617) len: 8:20:00.
...and here is 5 hours from the day we think the lock losses damaged the OMC (this includes the 5 lock losses reported in https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=28684 ).
4. H1:ASC-Y_TR_A_NSUM_OUT_DQ, raw,start: 2016-07-27 03:40:00 (1153626017) len: 5:00:00.
5. H0:VAC-EY_Y2_PT424B_PRESS_TORR, raw,start: 2016-07-27 03:40:00 (1153626017) len: 5:00:00.
6. H0:VAC-EY_Y3_PT410B_PRESS_TORR, raw,start: 2016-07-27 03:40:00 (1153626017) len: 5:00:00.
I don’t see any obvious relationship between these high power locks and vacuum pressure in the Y-end.
The last plot shows the first set of data with the vacuum channels highpassed 3rd order at 1Hz. Nothing visible.
Let me know if you’d like to chase this another way.
Images attached to this comment
Mike - Chandra's stated goal is to eventually continuously trend 7 AMUs (max allowed by software) at each building. The observance cited in this aLOG obviously would have been missed while in Faraday. Too bad that the RGAs don't live long with their SEMs on 24/7. As we install/commission the RGAs and as she works out the issues with the CDS and/or GC folks this trending will eventually be happening. J. Smith - The partial pressures that are changing are too small and not expected to show up on the total pressure gauges. From the graphic scans and knowing that the total pressure at the Y-end is 2 x 10-9 torr, we see that the partial pressures that changed are small (10-12 torr) - but still interesting because they are measurable and even more interesting if the changes can be shown to be tied to some IFO locking activity. (Science interesting? Who knew?)
Doh!!! Here are the .txt versions of the ASCII data
Non-image files attached to this comment
The indicated currents for these scans are typical of the SEM @ 1300 volts (which is the factory default). I have noticed in the past that setting the SEM voltage value in the EDIT tab does not change the value displayed in the device status screen or vice versa - so, though I set this to 1500 volts in one of those two fields, it may not have taken effect.