A boader look at ASC coherence to DARM. attached, sees some board lower coherences, but it is hard to say if they are just co-witnessing something or direct-cross sensing.

However for DHARD_Y and DHARD_P its pretty obvious even just looking at the power spectra that DHARD is seeing DARM signals like the bounce/roll modes and all of the Calibration lines.
The fact that all of the calibration lines are the same amplitudes in DHARD indicates this is a sensing issue.

In 2019 we did some investigations of this, with a similar conclusion (that the low frequency sensing function is impacted by DHARD being sensitive to DARM) 50511

Lockloss 20:00 UTC Most likely to wind gusts.
Lockloss screenshots attached.

While waiting for 50+ MPH winds to blow away, I started an Initial Alignment.
This was going well enough until the SUS SRM watchdogs tripped.
 

H1 is currently sitting IDLE, due to this wind.

 

This was my typo from last week, which didn't show up until today because the guardian was never loaded.  It should be correct now: 77656

SRCL coupling is indeed non stationary, as shown by the spectrogram attached, where DARM is shown before, during and after the noise injection. During the 3 minutes when the injection was constant, DARM shows non-stationary noise levels at low frequencies.

Computing a BLRMS of DARM between 20 and 50 Hz makes the non-stationary noise level evident. Comaparison of the BLRMS time series with ASC and LSC signals doesn't give much insight.

However, a scatter plot of the BLRMS vs all the ASC and LSC signals gives some hints that the noise is higher when DHARD_P is positive.

Plotting the BLRMS time series together with DHARD_P seems to confirm, although it's not a very strong correlation.

Approximately 3 days ago (when the recent rain system moved in late Friday) the temperature in both the Anteroom and Laser Room increased, along with relative humidity in both rooms.  This corresponds with the increase seen in PMC Refl, as well as a shift in the RefCav TPD (which moved higher before starting to drop again sometime yesterday), the output power of both amplifiers (both dropped slightly), and changes in all 8 of the system's pump laser diodes (most increased, a couple decreased).  The temperature change could cause alignment drifts (both pre-PMC and pre-amplifiers), as well as the change in pump diode power potentially causing changes in the output beam quality.  All of this could contribute to the shift observed in PMC Refl, RefCav TPD, and ISS diffracted power %.

Given our previous inability to recover much PMC Trans via beam alignment into the PMC, and the fact that changing the operating current of the pump diodes doesn't seem to "stick" for very long, my suspicion is that we are seeing slight alignment changes through the amplifiers.  This could cause a change in output beam quality, as the beam hits the thermal lenses formed in the amplifier crystals in a slightly different spot.  Correcting this requires bringing down the PSL entirely, then bringing it back up in stages (NPRO only, then NPRO + Amp1, then NPRO+Amp1+Amp2, then finally adding the PMC into the mix) while tweaking alignment and mode matching into each amplifier and ultimately into the PMC.  This takes too long for a standard 4-hour maintenance window, and might require more than a full-day maintenance window (alignment and mode matching into the amps/PMC has, in the past, been a multi-day effort; this took us a couple of days during our PSL recovery in March 2023).  Not clear how urgent this is, as we are still outputting between 108W and 110W from the PMC (depending on how recently we've "tweaked things up") and are only utilizing 60W for the IFO (leaving us roughly 50W of headroom).

[RyanS, TJ, Jenne]

We've had 2 locklosses today that seem to be about when that MadHatter Darm FM2 gets turned off.  But, since Sheila and Camilla moved the filter turning off, now the locklosses are happening a little later.

As Camilla points out, the ramptime of that filter inside Foton is very short.  I've increased it to 3 seconds and we're about to give it a try (since I don't have a better plan to try right now).  Something we haven't seen (since we're already locked right now) is whether increasing the ramp of that filter inside Foton causes trouble for the engagement of that filter, in DARM_OFFSET.

EDIT: Indeed we made it through the turning-off of the MadHatter filter with this 3 second ramp time (rather than the previous 0.1 sec ramp).  I am hopeful that it won't matter for the turning-on of the filter, since that happens in a quite stable part of the locking sequence.  But, we'll just have to see over the next few lock acquisitions.

Also EDIT: If we are unable to relock with this ramp time, attached is a screenshot of the previous ramp time, that we should revert to.

We've now relocked twice with the longer ramp time in the MadHatter filter in place for the turn-on and turn-off actions of that filter, so it seems fine to leave in place. 

In today's commissoning time, I first did the above measurements of PRCL coupling with and without the offset on, then later readjusted the SRCL gain ( 77648).  Below is a comparison of PRCL coherence with DARM before and after these changes (PRCL offset off, seems to have no impact, and SRCL FF retuned).  It seems that by retuning the SRCL FF, we have reduced the PRCL coherence with DARM.  Also shown is the PRCL coherence with SRCL, which is high at all frequencies.

In 77289 we reduced the PRCL coupling to SRCL and the MICH by phasing POP45 and retuning the LSC input matrix.  These didn't improve the PRCL coupling to DARM.

I'm no longer quite so sure about the conclusion that Pop18 is higher, or at least enough to really matter.

Here are 2 screenshots that I made extremely quickly, so they are not very awesome, but they can be a placeholder until Tony's much more awesome version arrives.  They both have the same data, displayed 2 ways.

The first plot is pop18 and kappaC versus time.  The x-axis is gpstime, but that's hard to interpret, so I made a note on the screenshot that it ranges from about April 20th (before The Big Shift) to today.  Certainly during times when the optical gain was low, Pop18 was also low.  But, Pop18 is sometimes high even before the drop in optical gain.  So, probably it's unrelated to The Big Shift.  That means that the big shift in the output arm is not responsible for the change in PRCL gain (which makes sense, since they should be largely separate).

The second plot is just one value versus the other, to see that there does seem to be a bit of a trend that if kappaC is low, then definitely Pop18 is low.  But the opposite is not true - if pop18 is low kappaC isn't necessarily low.

The last attachment is the jupyter notebook (you'd have to download it and fix up the suffix to remove .txt and make it again a .ipynb), with my hand-typed data and the plots.

I actually didn't load the guardian at the time of this change, so it didn't take effect until today.

So, we'd like histograms of DRMI acquitisiton times from before April 23rd, from April 23rd until today, and for a few weeks from today.

On the 2nd, Robert Anamaria and I found settings that would set the biases to these values, but the EY value hasn't been correctly applied in the automated relocks since. (77647) 

For ETMY, L3_LOCK_BIAS_OFFSET should be -4.9 while the L3_LOCK_BIAS_GAIN is -1 to produce a voltage readback of 200V.    I've reset this in the guardian, which I might have done last week with a typo.

This has now been loaded so shoud be at the correct value from 16:00UTC 07 May 2024 77674 .

Minhyo, Anamaria,

I've calculated the point at which the tail of the Gaussian laser beam should touch the PR2 scraper baffle to reflect about 60 mW, following Anamaria's idea.

Assuming that the estimated beam size at the PR2 scraper baffle is 7.47 mm, and the total beam power is 3 kW, the beam touches the side of the PR2 scraper baffle's hole at a position 15 mm away (4 sigma) from the center of the beam. I'll include the calculation later on how the beam is actually positioned within the 70 mm aperture of the PR2 scraper baffle.

The original alog referenced above (52184) has photos that show that the aperture of the baffle is visible at the same location as the beam when the interferometer is unlocked, and argues that this means that the beam is hitting the edge of the baffle aperture.

Minhyo

1) Made typo in above comment from mine. The estimated beam radius 7.67 mm -> 7.47 mm (edited on the original comment as well)

2) I'll elaborate the result of calculation in above (15 mm from the center) in below: 

Assuming the total power is 3 kW, the percentage of 60 mW power is 0.002%. Since the percentage of normal distribution for 4 sigma is 99.9937%, the partial integration in the upper limit is around 0.0032%.

Using this approximate number, I searched for the exact number to produce 0.002% with a 2D Gaussian beam model with a 3 kW power and 7.47 mm radius. From the beam model, it showed that integration from 4.11 sigma produces a power of around 0.0604 mW, suggesting that the beam is clipped at a point around 14.94 mm (4.11 sigma) from the center of the beam. I have attached a summary figure of my calculation.

Rechecked situation at LLO: https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=70996

TLDR: we see the same, but seems much lower power. Will measure when we get the chance.

Louis, Camilla. Investigations ongoing but the timing of this glitch is suspiciously when the H1:SUS-ETMX_L1_LOCK_L gain and filters are changed, tramp is 1secinds but FM2 and FM6 foton filters have a 3 seconds ramp. There is an INPUT to this filter bank before the gain and filters are turned on. Plot attached.

In 77640 we show that the DARM1 filter change is the cause of the glitches/locklosses.