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Entry  Tue Nov 10 12:41:23 2020, gautam, Update, IOO, 1W > IMC CD93A725-FB5C-4F67-BB2E-D122205114B0.jpeg
    Reply  Tue Nov 10 14:30:06 2020, gautam, Update, IOO, WFS2 broken  WFS2broken.pngWFS2broken_RF.png
       Reply  Fri Dec 4 15:58:22 2020, Koji, Update, IOO, WFS2 broken  
Message ID: 15670     Entry time: Tue Nov 10 14:30:06 2020     In reply to: 15669     Reply to this: 15708
Author: gautam 
Type: Update 
Category: IOO 
Subject: WFS2 broken  

While proceeding with the interferometer recovery, I noticed that there appeared to be no light on WFS2. I confirmed on the AP table that the beam was indeed hitting the QPD, but the DC quadrants are all returning 0. Looking back, it appears that the failure happened on Monday 26 October at ~6pm local time. For now, I hand-aligned the IMC and centered the beams on the WFS1 and MC2T QPDs - MCT is ~15000 cts and MC REFL DC is ~0.1, all consistent with the best numbers I've been able to obtain in the past. I don't think the servo will work without 1 sensor without some retuning of the output matrix.

It would appear that both the DC and RF outputs of WFS2 are affected - I dithered the MC2 optic in pitch (with the WFS loop disabled) at 3.33 Hz, the transmission and WFS1 sensors see the dither but not WFS2. It could be that I'm just not well centerd on the PD, but by eye, I am, so it would appear that the problem is present in both the DC and RF signal paths. I am not going into the PD head debugging today.


Looking back through the elog, 1mtorr is the pressure at which it is deemed safe to send the full power beam into the IMC. After replacing the HR mirror in the MCREFL path with a 10% reflective BS, I just cranked the power back up. IMC is locked. With the increased exposure on the MC2T camera, lots of new scattered light has become visible.

Attachment 1: WFS2broken.png  381 kB  | Hide | Hide all
Attachment 2: WFS2broken_RF.png  436 kB  | Hide | Hide all
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