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40m Log |
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Tue Oct 8 18:35:09 2019, gautam, Update, LSC, Locking prep
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Wed Oct 9 18:15:26 2019, gautam, Update, LSC, PRMI 3f locking
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Wed Oct 9 22:02:58 2019, gautam, Update, LSC, REFL55 whitening issue
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Thu Oct 10 01:12:56 2019, gautam, Update, LSC, Locking studies
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Wed Oct 16 11:42:17 2019, gautam, Update, LSC, Poor separation of PRCL/MICH in 3f signals
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Thu Oct 17 11:19:28 2019, gautam, Update, LSC, Locking activity last night 
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Tue Oct 22 00:52:27 2019, gautam, Update, LSC, Locking updates
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Tue Oct 29 01:24:45 2019, gautam, Update, LSC, More locking updates 
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Tue Oct 29 15:13:19 2019, gautam, Update, LSC, More locking updates
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Wed Oct 30 01:27:00 2019, gautam, Update, LSC, More locking updates
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Wed Oct 30 11:53:41 2019, gautam, Update, LSC, MICH loop shape tuning 
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Wed Oct 30 17:08:40 2019, gautam, Update, LSC, POP22 investigation
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Mon Nov 4 15:29:47 2019, gautam, Update, LSC, POP signal path
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Mon Nov 4 16:06:58 2019, gautam, Update, LSC, POP optical path    
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Tue Nov 5 11:52:27 2019, gautam, Update, LSC, Locking notes
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Wed Nov 6 02:08:48 2019, gautam, Update, LSC, Locking updates
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Wed Nov 6 17:05:45 2019, gautam, Update, LSC, CARM calibration  
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Wed Nov 6 17:45:34 2019, gautam, Update, LSC, ~
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Mon Nov 18 21:04:38 2019, gautam, Update, LSC, Locking - some ideas
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Wed Nov 20 01:07:18 2019, gautam, Update, LSC, Locking - progress
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Wed Nov 20 12:14:17 2019, gautam, Update, LSC, Locking - progress
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Wed Nov 20 17:20:24 2019, Yehonathan, Update, LSC, QPD Investigation
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Wed Nov 20 17:52:00 2019, gautam, Update, LSC, QPD MEDM screen update  
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Wed Nov 20 21:29:28 2019, gautam, Update, LSC, PRG ~13
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Fri Nov 22 00:54:14 2019, gautam, Update, LSC, locking notes
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Mon Nov 25 19:11:22 2019, gautam, Update, LSC, ALS noise re-look
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Wed Nov 27 23:24:01 2019, gautam, Update, LSC, No shaking but no inspiration either
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Sun Dec 1 13:38:48 2019, rana, Update, LSC, No shaking but no inspiration either
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Tue Dec 3 00:03:57 2019, gautam, Update, LSC, Green ALS also shows elevated noise with high arm buildup
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Wed Dec 4 19:54:27 2019, gautam, Update, LSC, A look to the past
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Thu Dec 5 01:54:39 2019, gautam, Update, LSC, Partial CM board path engaged
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Fri Dec 6 00:02:48 2019, gautam, Update, LSC, What is the correct way to set the 3f offsets?
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Fri Nov 15 12:08:04 2019, gautam, Update, LSC, POPDC whitening board
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Tue Oct 29 17:40:48 2019, gautam, Update, LSC, More locking updates 
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Message ID: 15040
Entry time: Wed Nov 20 17:52:00 2019
In reply to: 15039
Reply to this: 15041
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Author: |
gautam |
Type: |
Update |
Category: |
LSC |
Subject: |
QPD MEDM screen update |
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Koji and I had noticed that there was some discrepancy between the switchable gain stages of the EX and EY QPDs. Sadly, there was no indication that these switches even exist on the QPD MEDM screen. Yehonathan and I rectified this today. Both EX and EY Transmon QPDs now have some extra info (see Attachment #1). We physically verified the indicated quadrant mapping for the EX QPD (see previous elog in this thread for the details), and I edited the screen accordingly. EY QPD still has to be checked. Note also that there is an ND=0.4 + ND=0.2 filter and some kind of 1064nm light filter installed in series on the EX QPD. The ND filters have a net transmission T~25%.
After making the EX and EY QPDs have the same switchable gain settings (I also reset the trans normalization gains), the angular motion witnessed is much more consistent between the two now - see Attachment #2. The high-frequency noise of the sum channel is somewhat higher for EX than EY - maybe the ND filters are different on the two ends?
Note that there was an extra factor of 40 gain on the EX QPD relative to EY during the lock yesterday. So really, the signals were probably just getting saturated. Now that the gains are consistent between the ends, it'll be interesting to see how balanced the buildup of the two arms is. There still remains the problem that the MICH loop was too unstable, which probably led to to excess arm power fluctuations.
There is a mark on the QPD surface that is probably dirt (since we never have such high power transmitted through the ETM to damage the QPD). I'll try cleaning it up at the next opportunity. |
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