In investigating FC2 temperature trends to try and optimize SQZ, I ran into an oddity with FC2 OSEMs that was also seen by the FCES VEA Temps. Running through potential causes with TJ, we ruled that this was not a cause of H1 being unlocked since the other times H1 is unlocked don't have nearly as much noise in FC2.

There was a 7.6 EQ at this time, which explains the FC shaking and the lockloss. Why would the Temp_DEGF plots see a change too? Screenshot attached - the EQ arrives at T2 but it seems like the ripples in space temp are seen in T1.

We saw a strange violin ringup that was first seen in the DCPD windows and by the 500 Hz line growing, we found that ETMX 1, and 6 were ringing up. They're both at 511 Hz, as they were "anti-damping" the DCPDs were growing untill GRD finally turned them off. The monitors weren't showing much of an increase but the outputs were clearly diverging. Once the damping was turned off, the monitors grew. The damping and monitor filters for EX 1 & 6 are both 4th order.

Summary:

As "the last test before installation" I compared the dark noise level for all 8 PDs. Unfortunately the first PD in our own convention (top left when seen from the back, see this picture for PD number convention in the lab though it's probably different in the chamber) showed much larger noise level than all the others. See the first attachment left. (In this plot, PD 5 and 6 look noisier too, but this was found to be the preamp channels themselves.)

I swapped the entire PD assembly module (D1300130) for the noisy PD with the unit pulled from an incomplete spare ISS array assy originally removed from LLO HAM2 (S1202966) and measured the noise again. I also connected PD5 and 6 to the preamp channels for PD7 and 8 to remeasure the noise. Now no PD shows extra noise, see the right panel of the first attachment.

Note: Even though the plot title says "dark noise", the measurement is limited by the preamp noise and SR785 input noise (black trace). But this at least tells us that no PD is extra noisy. FYI the shot noise level for 10mA current is ~5.7e-11A/sqrtHz.

I checked the grounding of new PD1 unit (after temporarily disconnecting the SMP cables) and no shortcircuit was found.

I roughly aligned the newly installed PD1 but haven't done finer adjustment yet.

After PD1 position is finely adjusted, we'll have to repeat the jitter coupling measurement. 

Measurement Details:

All 8PDs were originally connected to two obsolete 4-channel transimpedance amplifier chassis (D1300639-v1) because they were available while spares for the latest ones (D1600193) weren't found. In this alog the channels of the first unit (S1301390) CH1-CH4 and those of the second unit (S1301386) CH5-CH8.

The output of the transimpedance stage (TP2 in the 2nd screen shot) was connected to SR785, 2 channels at a time. (Just for comparison, the 3rd screen shot is the transimpedance stage for the latest one (D1600193) which is pretty similar to the obsolete one except for the opamp (0.9nV/sqrtHz AD797 in the obsolete one VS 2.2nV/sqrtHz@1k TLE2027).)   I didn't use the whitening output as some of the channels of D1300639 weren't working (the output was railing).

Before swapping PD1, to make absolutely sure that the problem is PD not the preamp/SR785, I swapped the SMP-SMA cables for PD1 with those for PD2 at the back of the PD modules (i.e. PD1 goes to CH2 and PD2 to CH1) and the noise followed the PD.

The 4th attachment shows the noise level of the measurement. Red and blue traces were obtained by disconnecting two SMP-SMC cables from the preamp of CH1 and CH5.

CH1, 2, 3, 4, 7 and 8 were quite similar to each other, and CH6 was similar to CH5. In the end I had to swap cables for PD5 and PD6 to use CH7 and CH8.

"Preamp noise model" comprises the Johnson noise of 1.62k transimpedance, input voltage noise and input current noise of AD797 combined. I used typical 1kHz numbers here for AD797. The zero and the pole in the first stage are much higher than the measurement band here. Johnson noise of 10 Ohm (R7 in the second screenshot) in series with the PD won't matter in this measurement as well as when the PD is connected assuming that PD is a current source.

Other details:

The preamps are clearly labeled as D1300639-V2 (5th attachment), but the e-traveler for these boards (S1301390 and S1301386) say they're V1, and the actual board pattern (e.g. the first channel TIA opamp is U4, the transimpedance itself if R2 and the output of TIA opamp is connected to TP2 via R17, see the 7th screen shot) agrees with V1 (2nd screen shot) but not with V2 (6th screenshot).

I put "This is V1 not V2" label on both of the board. I also put "CH1 and CH2 noisy" label on S1301386.

Last week, Sheila recommeded that we switch the LASER_PWR guardian node to use the IM4 trans power channel to do the power scaling for the IMC (alog87545). After speaking with her today, we decided to make this change, but wait on the associated ASC/LSC gain changes. So, our kappa c will be off by 2 or 3 % until we update these gains. The plan would be to updated them tomorrow during maintenance recovery.

Following the success of Ryan Short's lock with these new gains (alog87573), we updated lscparams.py with CSOFT P = 30 and INP P = -2.

We reloaded all nodes that use lscparams.py, and checked Dave's GRD CFC screen to see the affected nodes. 

Mon Oct 20 10:09:15 2025 INFO: Fill completed in 9min 11secs

Lockloss after 16 hrs locked. Looks to be microseism caused.

TITLE: 10/20 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Observing at 150Mpc
OUTGOING OPERATOR: Tony
CURRENT ENVIRONMENT:
    SEI_ENV state: USEISM
    Wind: 4mph Gusts, 3mph 3min avg
    Primary useism: 0.04 μm/s
    Secondary useism: 0.45 μm/s 
QUICK SUMMARY:

IFO is in NLN and OBSERVING as of 00:58 UTC (14 hours)

After wind finally calmed down last night, IFO was able to lock and is still locked!

Plan for today is commissioning from 8:30 to 11:30 AM PT.

TITLE: 10/20 Eve Shift: 2330-0500 UTC (1630-2200 PST), all times posted in UTC
STATE of H1: Observing at 152Mpc
INCOMING OPERATOR: Tony
SHIFT SUMMARY: After H1 relocked at the start of my shift, I dealt with a brief ASC issue, then started observing. Been a quiet evening otherwise and the range has steadily been coming up over the past few hours. H1 has now been locked for 4.5 hours.
LOG:

• 00:39 - Reached NLN
  • Troubleshooting ASC ringup - alog87573
• 00:58 - Observing

H1 is back to observing as of 00:58 UTC after a long day of tussling with the environment, which still isn't great, but the wind has calmed down a bit.

After assisting DRMI locking by adjusting PRM, locking went automatically. Once we reached NLN, I noticed the 1 Hz ASC ringup starting. The most significant culprits I saw were CSOFT_P and INP1_P, so I adjusted their gains from 25 to 30 and -1 to -2, respectively. This seemed to stave off the rising ringup, and after about 15 minutes, I noted these loops and the PRG finally start to calm down. I returned the loop gains to their nominal and started observing. I can't say for sure if this works as a long-term fix for this ringup, but at least we didn't lose lock this time. I still see DHARD_P oscillating slightly at 1 Hz 10 minutes later, but it seems small at this point.

TITLE: 10/19 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Wind
INCOMING OPERATOR: Ryan S
SHIFT SUMMARY:

IFO is LOCKING at ACQUIRE_DRMI_1F

Bad day for the IFO due to the environment.

To start, the wind has not gone under 30Mph for the entire day, and has been over 35mph for the majority. It looks to be dying down now and will continue to do so this evening. Midshift report (alog 87565)

The microseism was sitting just at the 90th percentile point until 3 hrs ago when it started increasing.

We did get to NLN once but due to the known 1Hz CSOFT_P ringup (which previously was managed by increasing gain) but 4 minutes later, we had a Lockloss. (Lockloss alog 87571) This is an ongoing issue where it appears that long lock acquisitions experience the 1Hz ringup more violently than short acquisitions. Due to the microseism and wind, this has been the case for many of the recent locks. Ryan S has an alog about this correlation with a hunch that it is related to IFO thermalization (alog 87557)

In the next lock, since this is bound to happen again, we can either sit at MAX_POWER or increase the gain further (from 25 to 30) and see if either works. The former would test out the hypothesis in Ryan S's alog and the latter would just up the fix from before. 

14:30 UTC - shift start

14:54 UTC - TRANSITION_FROM_ETMX Lockloss

16:42 UTC - Initial Alignment - Fully Auto

17:12 UTC - IFO in IDLE due to WIND

18:36 - Lock Acquisition Attempt

19:35 - Succesful Lock Start

20:24 - NLN Reached (under 1 hr, fully auto)

20:28 - Lockloss due to 1Hz Ringup

22:07 UTC - IFO in IDLE due to MICROSEISM

22:54 UTC - Lock Acquisition Attempt

23:30 UTC - in DRMI, end of shift

LOG:

None

TITLE: 10/19 Eve Shift: 2330-0500 UTC (1630-2200 PST), all times posted in UTC
STATE of H1: Wind
OUTGOING OPERATOR: Ibrahim
CURRENT ENVIRONMENT:
    SEI_ENV state: USEISM
    Wind: 27mph Gusts, 16mph 3min avg
    Primary useism: 0.06 μm/s
    Secondary useism: 0.52 μm/s 
QUICK SUMMARY: H1 has been down most of the day due to high winds and microseism. I think the forecast says it'll calm down a bit this evening, but that remains to be seen. I'll have H1 keep trying for a bit, but may move it back to IDLE if unsuccessful.

• Wind high (30mph+ gusts all day), microseism alos above 90th percentile
• All other systems nominal

Lockloss due to 1Hz Ringup.

Closes FAMIS 27399. Last checked in alog 87406

Laser Status:
    NPRO output power is 1.856W
    AMP1 output power is 70.51W
    AMP2 output power is 139.5W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 26 days, 4 hr 48 minutes
    Reflected power = 24.74W
    Transmitted power = 106.7W
    PowerSum = 131.4W

FSS:
    It has been locked for 0 days 0 hr and 55 min
    TPD[V] = 0.5245V

ISS:
    The diffracted power is around 3.4%
    Last saturation event was 0 days 1 hours and 5 minutes ago

Possible Issues:
    PMC reflected power is high

Wind is still high. Microseism is rising now.

Managed a 2-minute DRMI lock and that's the highest we've gotten today. If we continue failing and the wind/microseism stays high, I will go into IDLE again until I see any improvements. 

Got called at 3:30AM due to DRMI lock unable to lock. Flashes seem bad since the earthquake and there hasn't been an initial alignment for some reason. Set IFO to initially align then turned the manager back on.

[Joan-Rene Merou, Alicia Calafat, Anamaria Effler, Sheila Dwyer, Robert Schofield, Jenne Driggers]

We have looked at the near-30 Hz and near-100 Hz combs (Detchar issue 340) in all of LHO Fscan channels (Full 148 channels list can be found in O4_H1_Fscan_ch_info.yml) to find witnesses and also channels where the amplitude and coherence change at the same dates as DARM.

The list of combs is the following one:


  

    

      
spacing (Hz)
      
offset (Hz)
    
  
  

    
29.9695138888
0
    
99.99845486125
70.02888889
    
99.99845679
0
    
99.99846
29.9694
    
99.9984722225
89.90847222
    
99.99865
0
    
99.99845
10.08992
    
29.96952
520.17208
    
29.9695211
589.9007589
    
29.96951374
760.22840625
  


As reported by Xuanye Fan in Detchar issue 296, "it can be determined that the high-order harmonics disappeared on April 8, 2024, and reappeared on July 7, 2024". Hence, we have compared coherence with DARM in all the channels and the difference between July 1st and July 7th 2024.

Following the findings by Xuanye, we have redone the comb time-evolution plots for all of these combs in order to check for dates where their amplitude changed. As can be seen in the plots below, there are two clear dates where changes in the behavior of the combs took place, April ~4th 2024 and July ~7th 2024. The attached plots to this post are similar to the ones generated by Fscan using FscanFineToothPlot plots, however, they have two differences: They use data from the non-normalized spectras instead of from the time average plots. Additionally, they compute the relative harmonic amplitude with respect to the median of the surrounding 1 Hz spectrogram. The attached plots confirm that there is a significant change in comb amplitude between April 4th and July 7th 2024. One clear example is shown here:



We list here the channels that do show most of these Combs. These same channels do show changes in coherence between July 1st and July 7th 2024, but do not show changes in the amplitude of the combs.

- H1_IMC-F_OUT_DQ
- H1_LSC-MCL_IN1_DQ
- H1_LSC-MICH_IN1_DQ
- H1_LSC-SRCL_IN1_DQ
- H1_PEM-CS_MAG_EBAY_LSCRACK_X_DQ
- H1_PEM-CS_MAG_EBAY_LSCRACK_Y_DQ
- H1_PEM-CS_MAG_EBAY_LSCRACK_Z_DQ
- H1_PEM-CS_MAG_LVEA_INPUTOPTICS_X_DQ
- H1_PEM-CS_MAG_LVEA_INPUTOPTICS_Y_DQ
- H1_PEM-CS_MAG_LVEA_INPUTOPTICS_Z_DQ

In most channels, the comb amplitude tends to get quite low after ~1500 Hz. The following sets of channels show differences between X, Y and Z:

- H1_PEM-CS_MAG_EBAY_SUSRACK_X_DQ (Higher amplitudes and towards higher frequencies)
- H1_PEM-CS_MAG_EBAY_SUSRACK_Y_DQ (Lower comb amplitudes)
- H1_PEM-CS_MAG_EBAY_SUSRACK_Y_DQ (Lower comb amplitudes)

Regarding CS_MAG_LVEA_OUTPUTOPTICS, these combs can be seen best in X, weaker in Y and almost non-existent in Z. (In CS_MAG_LVEA_INPUTOPTICS they look roughly the same height)

- H1_PEM-CS_MAG_LVEA_OUTPUTOPTICS_X_DQ (Strongest)
- H1_PEM-CS_MAG_LVEA_OUTPUTOPTICS_Y_DQ (Weaker lines)
- H1_PEM-CS_MAG_LVEA_OUTPUTOPTICS_Z_DQ (Almost no lines)

Same behavior at:
- H1_PEM-CS_MAG_LVEA_VERTEX_X_DQ (Strongest lines)
- H1_PEM-CS_MAG_LVEA_VERTEX_Y_DQ (Weaker lines)
- H1_PEM-CS_MAG_LVEA_VERTEX_Z_DQ (Almost no lines)

We can see that these combs mostly appear in the corner station. The combs do not appear in neither EX nor EY channels. However, comb 99.99865 Hz offset 0.000 appears in many EX, EY channels and does become more coherent after July 7th. However, it is very close to 100 Hz so it may be influenced by other round-number combs (?)

Tuesday Aug 19th I moved the dust monitor #10 from the bier garten area to up on the work platform on BSC2 (alog86444). Attached are some various plots of DM10 and DM6, the monitor next to HAM6 in the mega clean room (turned off atm).