J. Kissel, S. Dwyer

As opposed to the ''glitch'' I reported this morning (LHO:84622) which was while the IFO was configured in PRX and ISC loops created a large pitch excursion with M1 drive of the H1SUSBS. We're now seeing stuff that is much more "classic optical lever glitching" with the IFO configured in PRMI, with MICH ASC engaged. See attached. This is after Sheila/Camilla increased the current in the BS oplev laser this morning (LHO:84616)

As a reminder, Beam Splitter optical lever loops are only used in PRMI / DRMI until MICH ASC is turned on. The transition happens in the ISC_DRMI guardian, in the "ENGAGE_DRMI_ASC" (index 80) state; the gain in the ASC-MICH banks are ramped ON in 2 seconds, and the gain in SUS-BS_M2_OLDAMP banks are ramped off with a 20 sec ramp (i.e. it's not that the inputs or outputs are switched on or off).

So, beam splitter optical lever glitching had been particularly painful in the past few days when working in PRMI and/or DRMI without the corner ASC loops on. But, now that we've found a good alignment, and fixed the REFLAIR phase (LHO:84630) we're able to quickly transition to using DRMI ASC, and become insensitive to the optical lever performance -- which continues to glitch.

Following up on Jennie's PRCL OLG measurements yesterday, 84604, I checked the phasing of REFLAIR 45 (the MICH sensor) while PRMI was locked. I used a template in userapps/lsc/h1/templates/phase_REFLAIR.xml, but had to turn the PRM excitation down to 300 counts. 

THe first attachment shows that improving this phase improved the shape of the PRCL loop.  This has probably been not phased well for a while, not as a result of the vent. 

I also adjusted the phase of REFLAIR 9, SDFs attached.

Wed May 28 10:15:55 2025 INFO: Fill completed in 15min 51secs

Oli, Elenna

The DC1 and DC2 centering loops have seemed to be way too slow, so Oli and I took some transfer functions of the centering loops. We started with DC2 Y, and the loop didn't even seem to have a UGF. By looking at the phase, Oli and I determined that we could raise the loop gain to get a UGF of about 0.5 Hz with a phase margin of 38 degrees. This involved raising the gain from -0.1 to -8.

The DC1 and 2 yaw loops have the same design and feedback to the same suspensions, so we copied over the gain change and ran a quick OLG to confirm the result is the same.

DC1 and DC2 pitch also have the same design. The low pass filter in use in pitch cuts off at 0.7 Hz instead of 1.5 Hz like the yaw loops, so there was much less phase margin. Oli and I copied over the butterworth low pass at 1.5 Hz in the yaw loops to the pitch loops and found that raising the gain from -0.1 to -7 gave the desired 0.5 Hz UGF.

All four loops have been measured using the templates in [userapps]/asc/h1/templates/DC_centering and saved. I have attached screenshots of DC2 Y and DC1 P. We SDFed these changes.

We copied over the DC1/2 design to DC6 yesterday, so Oli and I also updated the low pass filter in DC6 P to match and SDFed. The gain of DC6 P and Y still needs to be checked.

As a final note, we lowered the bandwidth of these loops just before O4 to avoid noise reinjection into CHARD, so we should check how this higher bandwidth impacts the noise in CHARD at a later date.

J. Kissel, S. Dwyer, others

Just so others can see what we're seeing, here's the glitch at 2025-05-28 15:36 UTC that drove us to swap the F1/F2/F3/LF Triple Top coil driver on the H1SUSBS. 

Everything's wrapped in loops, so it's difficult to point fingers at any one component.
ISI is in FULLY_ISOLATED_NO_ST2_BOOST per normal for MICH lock acquisition
SUS has 
    - M1 OSEM PD to M1 OSEM Coil damping loops ON (L, T, V, R, P, Y)
    - M3 Oplev QPD to M2 OSEM Coil damping loops ON (P and Y)
The IFO was attempting to lock PRX.
This is unexpected, but apparently there's also some slow ISC loop that is really causing the majority of the alignment excursion.

Will keep investigating other times to see if this is a consistent issue. 
We've looked at a few other times where we suspect optical lever glitching, but the same ISC loops were not on.
Difficult to trend the configuration of the ISC loops at the moment, 'cause folks are trying lots of different configurations to get DRMI relocked.

We'll post if we find an answer.

We swapped the coil driver because the "glitch" showed up "most" in the F1 sensor, and we feared it was something like we've seen in the past -- SR3 top mass coil driver failures that took us a long time to find (see LHO:62038 and LHO:62123).

J. Freed

The reason we picked the ZFL-500HLN amp for SPI's Double Mixer was that it was an amp that met requirements from minicircuts

-frequency range contains 80MHz (our operating frequency)

-Operates at voltage supplied by Low Noise Power(15V, 17V, 24V etc.)

-Has a P1dB well above our output power of 10dBm (to remove non-linearity)

-No heat sinks (to fit in a 1U chassis.) (This requirement actually doesnt matter, the ones discussed here are still the best even compaired to amps with heat sinks)

-sma connections

-Low noise

-Low gain (we only need ~8dB of amplification)

The ZFL-500HLN was chosen because it fit all those requirements, with the cavieat of having to attuniate before amplification (adding noise). Though if I am correct and the Low noise power board 5V Vcc port is capable of supporting a 63mA load, another option would be the ZX60-P105LN+ instead due to the lower gain and lower noise. This would remove the need for an attinuator before amplification but its low input return loss means alot of power is reflected back towards our mixers (Also causeing noise). So it becomes a pick your poison of adding noise by attinuating before amplification vs by reflections back into our mixers. In practice, I believe both would operate about the same. Will add a comment if something changes

Double-MixerAmpComparison.png shows a quick comparison of the 2 amps

J. Kissel

As we begin to investigate transient issues with the Beam Splitter where its sensors are reporting intermittent glitching that is spoiling DRMI locking, the optical lever damping loops are always an open question for me. 

Here's the impulse response of the filters, shown both as a normal time-series, which shows that most of the action happens within the first 0.2 seconds. I also show a semilogx plot of the time series to show the early magnitude of the response.

Finally, I attach a screenshot of which filters are on.

Sheila, Camilla

As we've had trouble catching PRMI, and there is some signs of the BS oplev laser glitching, see attached. We turned up the laser current so that the Oplev NSUM counts increased from 16,000 to 20,000. BS Oplev laser is in the cooler behind the HWS table / TCSX rack.

TITLE: 05/28 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
CURRENT ENVIRONMENT:
    SEI_ENV state: CALM
    Wind: 5mph Gusts, 0mph 3min avg
    Primary useism: 0.13 μm/s
    Secondary useism: 0.10 μm/s
QUICK SUMMARY:

H1 currently in ready state.
Seimic system back to calm after a few earthquake.
I got ALS Locked after touching up Y arm.
I'm going to Try to get DRMI locked for the Comissioners, before they arrive. Im going to try once with out a Full Initial Alignment first and then run an initial alignment since the alog 84610 has it in bold, perhaps I should try it.
 

TITLE: 05/28 Eve Shift: 2330-0500 UTC (1630-2200 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY: More progress this evening with H1 locking! We've been able to reach 'RESONANCE' and set the green references there, but DRMI/PRMI locking has continued to be a struggle where flashes will look good, but it will not lock for a long time for some reason. See other logs, mainly alog84610, for details.

As Elenna mentions in her log, first thing in the morning a FULL initial alignment should be run! [Tagging OpsInfo]

LOG:

Ryan S., Sheila, Elenna

First thing Wednesday morning: run full initial alignment with green cameras

Ryan and I were able to lock the IFO on DRMI after many hours struggling down rabbit holes. In short: we were able to finally lock DRMI after reverting the ITMX and ITMY alignment to the alignment on Friday, and running manual initial alignment.

Sheila came online while we were in DRMI checking various things, and together we made it to CARM on Resonance. The alignment was very good (mostly hand tuned except for MICH ASC and DHARD). Sheila and I did our usual check of the PRG following alog 62110 and confirmed that everything looks great.

From there, Ryan and I ran the green camera offset scripts, watched them converge, and set the camera values. These are all SDFed- Ryan will add screenshots. To reiterate: run full initial alignment!

Sheila will add comments about checking and fixing the REFL phases.

While Sheila was adjusting the REFL phases so we could go to CARM on analog, I tried setting up the POP X centering using PM1 (so we could do DRMI on POP). I confirmed that moving PM1 moves the beam on POPX in reasonable ways. I had to flip the DC centering sign to positive when I engaged the loop, DC6, so the centering would converge. I was trying to check the UGF of the DC6 pitch loop by adding an offset to the loop, and accidentally added a massive offset, which tripped a lockloss since the beam went crazy on POPX and therefore LSC POP and that's a lockloss trigger diode.

I also had to turn on the PM1 signal output from the ASC model, which I then SDFed. After lockloss, the PM1 locking output doesn't get cleared, so Sheila will add that to the list of suspensions to clear after lockloss.

The chiller systems at the mid stations were started this morning for the season.