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jenne.driggers@LIGO.ORG - posted 16:59, Tuesday 14 May 2019 - last comment - 20:03, Tuesday 14 May 2019(49245)
Resetting initial alignment setpoints (preparing to; not done yet)

We haven't reset our initial alignment setpoints in a long time, and it likely needs redoing. 

In prep for resetting the initial alignment setpoints, we need to have the IFO aligned and converged, but held at 2W.  We also need the green shutters open and the green lasers locked on the TEM00 mode.  With our current IR alignment and green QPD setpoints, the Xarm green doesn't want to lock on the 00 mode.  Last lock I had opened the green shutters before the ADS loops came on for the arms, and the Xarm was locked on 00 for green, so I started running the green QPD setpoint script so that the green beam would follow along as the soft ADS loops converged.  This seemed to be working, and the QPD offsets that had the Xarm green locked were:

ALS-X_QPD_A_PIT = -0.268

ALS-X_QPD_A_YAW = 0.708

ALS-X_QPD_B_PIT = 0.955 (this is extremely close to the edge, but it seemed okay hanging out here. The current value is 0.841)

ALS-X_QPD_B_YAW = -0.177

So, I think we should be able to slowly walk the offsets to this place during a future lock, or to use them for initial alignment if we also change the camera setpoint to be 251.2 for pitch, and leave yaw at the current value of 332.9 (the yaw CAM_ITM_YAW_ERR was basically zero, but the pitch was about 0.19).  These setpoints wouldn't be our final answer for initial alignment setpoints, but would make it such that the Xgreen would lock on the 00 mode when the IFO is aligned with IR.

A somewhat confusing side note is that changing the QPD setpoints while in lock seems to have broken the lock twice when taking steps of size 0.1.  Not totally sure why, but we're going to try this time to acquire without touching the offsets.

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jenne.driggers@LIGO.ORG - 18:26, Tuesday 14 May 2019 (49247)
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[Sheila, Jenne]

We have now reset the X and Y green initial alignment setpoints.  Both arms' B pit offsets are extremely large - 0.96 - so we will need to pico these at some point, unless with the higher input power we decide that we need to move our spots (hopefully in a way that bring these closer to zero).

sheila.dwyer@LIGO.ORG - 20:03, Tuesday 14 May 2019 (49248)
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Attached is a screenshot of the QPD and ITM camera offsets after we reset them.  We have now reverted this because we weren't able to make it through ANALOG CARM and DRMI on POP with the new alignment references.

We also found that the auto exposure was on for the ITMY green camera, it got turned on May 7th.  This was causing glitches in the Y camera loop, we have turned it off.  

We lost lock while powering up after this, so Niko ran an initial alignment.  

  • We tried out the convergence checker for the green wfs, I tightened the convergence checker for the camera DOFs a bit.  
  • The X arm camera servos were extremely slow, much slower than Y.  The gain were set low because of some lines in the guardian that set them low if the camera is away from zero to start.  For now I took this out, so that the camera servos will always come on with the same gain.  If it does turn out to be necessary to engage them with reduced gain sometimes, we should edit the code to be sure that it will later set the gains to nominal.  When the loops run this slowly, it is painful to wait for them to converge.
  • The combination of these things mean that the operators should now be able to simply request GREEN_WFS_OFFLOADED to do initial alignment with the green arms, and it should go more quickly than it often has in the past. 
  • We also found that the MICH dark state didn't work at first, saturating the  beamsplitter.  This is common, and there is a check for it in the code, but the check was not working, so I've edited it.  

Since we had so many locklosses this evening, we noticed a few more things that we could improve in the locking sequence. 

  • The ALS Diff gaurdain is written to save the most recent found IR offsets to a text file, but wasn't doing this because of a threshold on the IR power.  We changed the check to look at a 5 second average of the transmitted power. 
  • The ASC convergence checkers were taking more than 10 minutes because of the strict threshold on PRC2, we set the threshold to 1000 (it was 600 in several places), so hopefully this will speed things up. 

We had a 0.5Hz pitch instability when reducing the RF45 modulation depth twice today, the second time I turned back on the 0.5 Hz notches in the pitch refl centering loops, which we had turned off last thursday (49160) (turning them off hadn't caused any problems until tonight).  

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