The peak is also visible in the DARM spectrum. In this plot the peak is at 3335 instead of 3340 Hz. Why is there a 1.5% frequency shift?

Here are projected SRM thermal noise curves for structural and viscous damping.

Given a typical SRC coupling into DARM of 1×10⁻⁴ m/m at 40 Hz, 20 W of PSL power, and 13 pm of DARM offset (25019), this would imply a noise in DARM of 1×10⁻²⁰ m/Hz^1/2 at 40 Hz if the damping is structural.

When I modelled the optics in https://dcc.ligo.org/LIGO-T1500376 and in particular the surrogate SRM I had assumed optic was bonded. After looking again earlier with Rana and Betsy realised it is held with 2 set screws (Peek?) on barrell at 12 o'clock and two line contacts at 4 and 8 o'clcok. See https://dcc.ligo.org/LIGO-D1200886.

The previous bonded model for the SRM surrogate (I believe) had a fisrt mode predicted around 8k Hz. However, from a quick model I ran today (with the set screws etc ... ) the first mode appears to be around 3400 Hz. The mode is associated with the optic held with the peek screws. (Now I was doing model using remote desktop so I will need to check it again when I get a better connection, so more to follow on this. I will also post updated model, once I get back to Caltech.) 

The ~3340Hz peak is also clearly visible in the PDA/PDB x-correlation spectrum. See alog 26345.

A couple of comments on this topic:

• There is no feature at 3340 Hz in the L1 DARM spectrum, nor within several hundred Hz of this. So the main mode of the L1 composite SRM seems to be at a different frequency, though I think there has never been a transfer function measured there above ~1 kHz that would indicate the mode frequency (put on todo list). The first attached plot shows Kiwamu's full-O1 DARM and cross-correlation spectra for H1 and L1, zoomed in to the several kHz region. There are some peaks in L1 in the 4700-5100 Hz region, but it's fairly complicated in that region.
• The thermal noise peak in Evan's SRM plot is at a level of 2e-15 m/rtHz, which is a bit above the SRCL sensing shot noise level, so we should be able to see it in SRCL. The second attached plot shows a spectrum of the SRCL error signal from January 9, 2016. From the Aug 2015 entry 20270, the shot noise corresponds to a displacement noise of 1.3e-15 m/rtHz. In the attached spectrum, the mode peak (which is at 3320 Hz here - ?), is 2.5x above the shot noise level, putting it at about 3e-15 m/rtHz. This is a bit higher than in Evan's model, but it is actually remarkably close. (I didn't include it in this plot, but the DARM spectrum also shows this peak at 3320 Hz at this time, and there is 0.8 coherence with SRCL at the peak.)

Danny, Matt (Peter F remotely)

Due to the issues currently seen at LHO, we were asked how the LLO SRM surrogate was put together and if we could add to the alog for a record of the process. The easiest way is to do it via photos (which we have of the assembly process).

IMG_1462....There are only two setscrews that hold the optic in place. Can be seen putting these in place below in the "cup" that holds the optic (eventually). Im not sure of the material but Peter F's speculation is that "I think those set screws must be the carbon-loaded PEEK type. The only other option I can think of for a black set screw would be carbon-steel, and it surely isn’t that."

IMG_1455...Here you seen the three main parts. The optic, the “cup” that the optic goes into and then the main mass the cup goes in. Note in the “cup” you see the two raised parts at around 4 and 8 o’clock that the setscrews ‘push’ the optic onto. So its not 'really' a three point contact, its 2 points (set screws) and 2 lines (in the holder)

IMG_1466...Here is the optic going into the cup making sure the fiducial on the optic lines up with the arrow on the cup

IMG_1470.....Optic now in the cup and doing up the setscrews that hold it in place. I cant remember how much we torqued it up (we only did it by hand). But as Peter F again speculated that perhaps we just did the setscrews up tighter than LHO

IMG_1475....Flipping the cup (with the optic in it) over and placing in main mass

IMG_1478....Cup now sitting in Main mass (without screws holding cup into main mass)

IMG_5172......the SRM surrogate installed into the suspension

It looks like there might be a mode in the L1 SRM at 2400 Hz. See the attached plot of SRCL error signal from January, along with DARM and the coherence. There is also a broad peak (hump) around 3500 Hz in SRCL, with very low coherence (0.04 or so) with DARM. The SRCL data has been scaled by 5e-5 here so that it lines up with DARM at 2400 Hz.

Here are two noise budgets showing the expected DARM noise assuming (1) structural (1/f^1/2) SRM damping and (2) a hyperstructural (1/f^3/4) SRM damping. This hyperstructural damping could explain the DARM noise around 30 to 40 Hz, but not the noise at 50 Hz and above.

I also attach an updated plot of the SRCL/DARM coupling during O1, showing the effect of the feedforward on both the control noise and on the cavity displacement noise (e.g., thermal noise). Above 20 Hz, the feeforward is not really making the displacement noise coupling any worse (compared to having the feedforward off).

Note that the PEEK thermal noise spectrum along with the SRCL/DARM coupling is able to explain quite well the appearance of the peak in DARM.

I am attaching noise budget data for the structural case in 27625.

The 59Hz hump on the ITMY Stage2 Corner2 sensors was at 90hz a week ago and steadily marched down to 59.  It probably isn't doing too much harm at the moment but if it doesn't stop coming down...  It might be interesting to see how far it goes but I think this needs action.  A power cycle of the satellite rack is a good start.  This will happen in a couple days anyway...

This task has officially been added to FAMIS. Task Number was 6098.

I also just restored the CO2 QPD coefficients and the SIM_ITMX_SUB_DEFOCUS_CO2_GAIN to 3.57E-5

Good point.  The Ops Check Sheet has been updated to move the HEPI WD Counter check to Wednesday.  Thanks, Travis!

Driving an admixture of hard/soft is bad, as illustrated in these Bode plots. The left plot shows the PUM to UM TF in the optic basis, and the right one is in the hard/soft basis.

With different damping in the TOP stage, the actuation TF is different for each suspension and so we end up with some of these zeros that we see in the left plot. Matching the actuators should make the loop shapes more like the ones on the right, avoiding some of the multiple UGFs we see in measurements.

But what's a good way to make sure that we have pure hard/soft actuators? We don't have pure sensors.

Unfortunately the current RMS watchdog on the L2 stage of ETMX tripped at around 3:00 AM local this morning. This seems to have shut the drive signal of all four colis and therefore the ETMX mode was not damping at a good rate.

By the way, we were unable to untrip the watchdog from the control room using the SUS-ETMX_BIO_L2_RMSRESET channel. This seems to be a known issue (alog 20282). I drove to EX and power-cycled the PUM coil driver.

Travis opened an FRS for this issue of being unable to reset the watchdog of the current rms on the ETMX PUM (aka L2) driver.

Opened FRS Ticket 5616.

After the weekend power outage, we see that the ITMX M0 BIO settings are back to their nominal combo of:

STATE REQUEST  2.000

COIL TEST ENABLE   1.000

- And the BIT statuses all show green.

Toggling them to alternate 1.000 and 2.000 values respectively and back to niminal turns them from red back to green.  Nothing seems to be stuck now and the ill combo that Sheila reported the other day above doesn't seem to be a problem now.

We also tried running the Hang's automatic lockloss tool, but it is a little difficult to interpret the results from this.  There are some AS 45 WFS channels that show up in the third plot that apprears, which could be related to either a glitchy SR3 or an RF problem. 

One more thing: Nnds1 chrashed today and Dave helped us restart it over the phone.

For the three locklosses that Sheila plotted, there actually is something visible on the M3 OSEM in length. It looks like about two seconds of noise from 15 to 25 Hz; see first plot. There's also a huge ongoing burst of noise in the M2 UR NOISEMON that starts when POP18 starts to drop. The second through fourth attachments are these three channels plotted together, with causal whitening applied to the noisemon and osem.

Maybe the OSEM is just witnessing the same electrical problem as is affecting the noisemon, because it does seem a bit high in frequency to be real. But I'm not sure. It seems like whatever these two channels are seeing has to be related to the lockloss even if it's not the cause. It's possible that the other M2 coils are glitching as well. None of the other noisemons look as healthy as UR, so they might not be as sensitive to what's going on.

RF "problem" is probably not a real RF problem.

Bad RFAM excess was only observed in out-of-loop RFAM sensor but not in the RFAM stabilization control signal. In the attached, top is out-of-loop, middle is the control signal, and the bottom is the error signal.

Anyway, whatever this low frequency excess is, it should come in after the RF splitter for in- and out-of-loop board. Since this is observed both in 9 and 45MHz RFAM chassis, it should be in the difference in how in- and out-of-loop boards are configured. See D0900761. I cannot pinpoint what that is but my guess is that this is some DC stuff coming into the out-of-loop board (e.g. auto bias adjustment feedback which only exists in out-of-loop).

Note that even if it's a real RFAM, 1ppm RIN at 0.5Hz is nothing assuming that the calibration of that channel is correct.

Correction: The glitches are visible on both the M2 and M3 OSEMs in length, also weakly in pitch on M3. The central frequency looks to be 20 Hz. The height of the peaks in length looks suspiciously similar between M2 and M3.

Just to be complete, I've made a PDF with several plots. Every time the noise in the noisemons comes on, POP18 drops and it looks like lock is lost. There are some times when the lock comes back with the noise still there, and the buildup of POP18 is depressed. When the noise ends, the buildup goes back up to its normal value. The burst of noise in the OSEMs seems to happen each time the noise in the noisemons pops up. The noise is in a few of the noisemons, on M2 and M3.