Sheila, Jenne, TJ, Ryan, Keita, Jennie W
Today we had trouble locking from the start of the commissioning period. This seems to have been a problem with OMC locking - see Ryan's log for further details.
We scanned the OMC in single bounce anmd everything seemed to look ok.
We managed to power up but then eventually lost lock after Sheila measured LSC FF and Robert took some photos at viewports.
Alena had suggested a better spot we could be aligned to on the OFI (second column on second last page), so since we have been having locking problems since maintenance on Tuesday we decided to unlock and try this move.
The best spot suggested is so far off that we know we will have to use the HAM6 picomotors to recentre the beam on the AS_A, AS_B and AS_C QPDs.
TJ and Jenne slowly brought us to this new spot (between two t cursors in this image) while also using picomotors 2X, 3X, 3Y, 1X to keep us centred on AS_A, AS_B and AS_C. During this time we were also trying to run the DC centering loops on OM1 and 2 to keep us centred on AS_A and AS_B, unfortunately we then ended up in a situation where we were saturating OM1, 2 and 3 and OMC suspensions at different points. Turning off the DC centering loops relieved OM1 and 2.
We couldn't get past PREP_DC_READOUT_TRANSITION.
Before doing this, at 22:50 UTC Sheila and I measured the spot positions on the SRM and SR2 mirrors using the A2L gains.
Sheila tried to releive the OMC and OM3 suspensions using their sliders but eventually we realised that we might have to do a combo of this with more pico-motoring to lock the OMC and power up.
This is shown in this image, however, these efforts eventually unlocked us.
Here is another ndscope showing the full days efforts with the ISC_LOCK guardian state also.
If we decide to stick with this new alignment, we'll need to update the thresholds in SRC align when acquiring SRY so that H1:LSC-SRCL_TRIG_THRESH_ON is something like 0.003 (so, half of its current value of 0.006), and the _OFF is similarly lowered. Maybe not a full half, but some lowering.
Also, we are somewhat concerned about the throughput in this position. AS_C yesterday when centered had an NSUM of about 0.0225, but today when centered is about 0.18. However, when we were doing SR2 single-bounce alignment as part of initial alignment, AS_C was at 0.0218. So, some of the loss of NSUM on AS_C happens when we center on it. This is rather consistent with AS_A and AS_B sums thinking that we still have similar throughput through the OFI today as compared to yesterday.
Also, when we were at PREP_DC_READOUT_TRANSITION, I spent a while with Ibrahim offloading OM3 and OMC by changing the spot position (via picomotor) on the AS WFS. I think Jennie shows this in her second to last plot.
I spent a while moving things to get the OMC QPDs closer to their setpoints. Then, with the OMC ASC loops engaged (with OM3 and OMC not quite saturating), I moved the picomotors in front of AS_A and AS_B to get OM3 and OMC farther from saturation. This part (the offloading, after OMC ASC was on) is shown in the attached image. After I had offloaded OM3 and OMC, I requested OMC_LOCK to lock the OMC, and we were able to go to DC Readout. As Jennie notes, after we got to 10W I was worried that OM2 was going to saturate, so I made one more click on Motor 2 to change the pointing on AS_B, and that caused a lockloss (even though the same clicks at 2W on RF DARM were safe). The last little bumps in the most recent 5 mins of this xaxis are the power up to 10W.
When you make a big alignment change upstream of HAM6 and you find that WFS centering won't work without pico, the only cure is pico-ing, but confirm that the OMC QPDs are OK before locking IFO.
The right sequence is something like this:
Using single bounce beam, enable WFS centering. If nothing rails, turn on the OMC ASC, nothing should rail again, be happy.
If OM1 and/or OM2 rail by WFS centering, eventually you'll have to pico, but don't pico right away. Instead, do the following.
- Disable WFS centering and clear the ASC input for OM1/2/3 as well as OMCS. Record the OMCS suspension slider numbers and zero them (i.e. OMCS will be freely hanging).
- If you don't see the beam on OMC QPDs, use OM1 and 2, or OM1 and 3, to find it.
- Use OM1/2/3 to center OMC QPDs. No one suspension among OM1/2/3 should have much larger alignment offsets than the others.
- If you want you can use OMC ASC to control OM1/3 and manually move OM2 (modify the output matrix like alog 65035), or control OM1/2 and manually move OM3.
- If you cannot center them no matter what, you will have to touch OMCS. (But at that point you know that things are really off.)
- Once satisfied, if you used OMC ASC, relieve the OMC ASC input to the OM1/3 using alignment sliders, turn off the OMC ASC, and revert the output matrix.
- Turn on the OMC ASC. See how close to saturation OMCS and OM3 are.
- Use OM1 and OM2 to relieve OMCS and OM3 if needed.
- The beam should be on AS_A and AS_B at least a bit. If not sure, use OM1 and OM2 so the beam goes closer to the center, which might make the OM3/OMCS OSEM output bigger.
- Once you know that the beam is there on AS_A and AS_B, pico.
- Turn on the WFS centering.
- pico further if you think you can relieve suspensions, but don't make OM3/OMCS worse.
- If things work, be happy, relieve all OM and OMCS suspention alignment input using suspension sliders, then turn off the OMC ASC and WFS centering. Proceed to IFO locking.
This is pretty much the same as what you do after changing AS path and/or OMC in HAM6. By working on AS path alignment before locking IFO, you don't have to worry about IFO lockloss by upsetting ASC-AS_A, kicking HAM6 electronics by HV pulses sent to picos and/or making huge vibration in HAM6.
When manually aligning the beam into OMC using OM1 and OM3 (or OM1 and OM2, or combination of OM1, 2 and 3), it's convenient to remember that ASC-OMC_A is far field and OMC_B is near. It seems that that's the case as of now.
You always want to use the mirror closer to the OMC (like OM3) to center the far QPD (OMC_A) and the far mirror (like OM1) to center the closer QPD. Iterate this and things converge.
Even when you only see the beam on one QPD, you can use the above rule. For example, if your beam is on OMC_B but not on OMC_A, you will scan OM3 by a large amplitude to find the bean on OMC_A. It doesn't matter if you lose the beam on OMC_B at this point, next thing to do is to scan OM1 to regain the beam on OMC_B. Iterate and you'll find the beam on both of the QPDs at some point.