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Entry  Wed Oct 28 20:42:53 2020, Koji, Update, General, Vent Prep 10x
    Reply  Thu Oct 29 12:43:35 2020, gautam, Update, General, Vent Prep preVentAlignment.pngPRMIcarr_PRMalignment.pngALS_ool.pdflowPowerMC.png
       Reply  Thu Oct 29 19:30:56 2020, gautam, Update, General, Vent complete ventValveStatus.pngvent_Oct2020.jpgventValveStatus_overnight.pnglowPowerIMC_afterVent.png
          Reply  Mon Nov 2 12:44:25 2020, gautam, Update, General, ETMY and OMC chamber heavy doors off CB84FD62-C48B-414F-8825-50C9DE0B47CF.jpeg
             Reply  Mon Nov 2 16:46:06 2020, gautam, Update, General, Plan for OMC chamber IMG_2318.JPGIMG_2332.JPG
                Reply  Mon Nov 2 17:13:19 2020, Koji, Update, General, Plan for OMC chamber 
                   Reply  Mon Nov 2 17:32:05 2020, gautam, Update, General, Plan for OMC chamber IMG_2317.JPG
Message ID: 15651     Entry time: Thu Oct 29 12:43:35 2020     In reply to: 15649     Reply to this: 15652
Author: gautam 
Type: Update 
Category: General 
Subject: Vent Prep 
  1. Oplev HeNe at ETMY was replaced, see here for my earlier discussion on this.
    • I thought this is a good idea since we want the Oplev as a coarse reference and it'd not be ideal if this HeNe dies during the time the optic is out of the chamber.
    • New HeNe had 2.8mW of power output as measured with Ophir power meter. This is in line with what is expected from these Lumentum heads.
    • I labelled the head with the power output and today's date, re-aligned the Oplev reflection onto its QPD. 
    • After this work, the Y-arm could be locked without the huge angular fluctuations that was visible earlier, 👍 .
  2. GTRY anomaly
    • I actually judged that there is no anomaly.
    • The GTRY CDS indicator is actually quite useless - the ADC saturates at ~3500 cts (and not 32768 as you would expect from a 16 bit ADC but that's the well-known whitening filter saturation problem). This should be fixed, but this is a task for later.
    • I measured with a DMM the voltage when the TEM00 is locked to the cavity and GTRY is 0.3 (the nominal value these days), the DC voltage was ~5.6 V. The prompt reflection from the ETM registers ~6.5 V DC. So the mode-matching isn't stellar, but this is again a known issue, and can be fixed later.
  3. Other pre-vent checks
    • The Oplevs had drifted significantly, I re-centered ITMs, ETMs and BS after aligning the arm cavities and green beams in the POX/POY lock state. See Attachment #1.
    • I locked the PRMI on carrier and used this config to re-center the PRM Oplev, see Attachment #2.
    • No further action was taken regarding SRM oplev.
    • I checked the ALS noise, see Attachment #3. The X arm ALS has excess noise at ~100 Hz that certainly wasn't there previosuly - sigh. There is nothing I can find about any changes made at EX in the elog.
    • Updated the "DriftMon" values, though I guess we don't even really use this anymore these days?
    • Re-relieved the IMC WFS offsets.
    • Cut the input power to the IMC from 1.007W to 100.1 mW (both numbers measured with Ophir power meter).
    • Replaced the 10% beamsplitter in the MCREFL path on the AS table with a Y1 HR mirror. Note that there is no beam on the IMC WFS in this configuration.
    • Was able to lock the IMC on low power to a TEM00 mode - need to set up the low power autolocker. The IMC autolocker is now set to the low power settings, and I've tested it locks a couple of times. Attachment #5 shows the low power lock in StripTool.
    • Walked around and looked at all the bellows - the jam nuts are up against their stops, and I can't move them with my hands, so I think that's okay.

If everything else looks good, I'll start letting the dry N2 into the main volume after lunch.


Now the green transmissions are visible by the green PDs. Attachment 9 shows the trans and ref of each green beams with and without locking to TEM00. The questionable green TRY was ~0.3. If we compare this with the histrical data (Attachment 10), it is about 1/4 of the value in the past. It's not too crazy but still quite low.

BTW, nice video! @ Koji, How difficult was it to edit it into this form? 

Attachment 1: preVentAlignment.png  283 kB  Uploaded Thu Oct 29 14:33:13 2020  | Hide | Hide all
Attachment 2: PRMIcarr_PRMalignment.png  235 kB  Uploaded Thu Oct 29 14:33:18 2020  | Hide | Hide all
Attachment 3: ALS_ool.pdf  518 kB  Uploaded Thu Oct 29 14:35:31 2020  | Hide | Hide all
Attachment 4: lowPowerMC.png  55 kB  Uploaded Thu Oct 29 15:59:57 2020  | Hide | Hide all
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