This is actually FM2.

I was texting with Mike to see if taking H1 out of Observation Mode (when L1 is down) for this test was OK by him, and he concurred.  This work is referenced by Work Permit #5505.  In the work permit, I see a time of 9/21-25 for Period of Activity.  So Operators can allow this activity during this time since Mike has signed off on the work permit.  (perhaps in the future, we can reference the work permit in alog entries so Operators will know this is an acceptable activity.)

I'm not totally sure about when to make the decision to preemptively turn ON this filter if we get a warning of an impending EQ.  It's not totally clear to know which types of EQ will knock us out and which won't.  I guess I can look to see if (1) Terramon gives us a RED warning, and also (2) watch 0.03-0.1um/s seismic signal for an order of magnitude increase.  Perhaps in that case I could then end Observation Mode and turn ON the filter and stay out of Observation Mode until L1 comes back.  (sorry, just trying to come up with a plan of attack in case L1 drops out)

As it stands, L1 has been locked for 10hrs, so we'll keep an eye on them.  I asked William to contact me if they drop out (but I'll also watch the FOM & GWI.stat.

I believe that by switching this, while in 'Undisturbed', it will show as an SDF diff thereby automatically taking us to 'Commissioning' mode until the diff is accepted, the ODC Intent ready bit is Green(again) and we can once again click the intent bit to 'Undisturbed'. I asked this at the JRPC meeting yesterday.

Apologies for the wrong FM number, and in the future I'll try to rememver to put the WP number in the alog.   Operators can probably stop toggling this filter for now.  We will put this on the list of minor changes that we will make on maintence day, so that next tuesday it can be added to the guardian and the observe.snap, along with some HSTS bounce and roll notches. 

Recall that Stefan made changes to the OMC Power Scaling on Sunday 13 September 2015 (in the late evening PDT, which means Sept 14th UTC). One can see the difference in character (i.e. the subsequent consistency) of kappa_C after this change on Sudarshan's attached plot. 

Once can also see that, for a given lock stretch, that the change in optical gain is now more that ~2-3%. That means that ~5 [Mpc] trends we see on our 75 [Mpc] the in-spiral range, which we've seen evolve over long, 6+ hour long lock stretches, cannot be entirely attributed to optical gain fluctuations as we've been flippantly sure of, and claiming.

However, now that we've started calculating these values in the GDS pipeline (LHO aLOGs 21795 and 21812), it will be straight-forward to make comparative plots between the calculated time dependent parameters and every other IFO metric we have. And we will! You can too! Stay tuned!

Just to drive the point home, I took 15 hours' worth of range and optical gain data from our ongoing 41+ hour lock. The optical gain fluctuates by a few percent, but the range fluctuates by more like 10 %.

I strongly suggest we add EPICS mirrors of these channels (similar to what was done for the sensemon range). This will ensure that (1) they are available in dataviewer, and (2) we have trend data of these channels. We want to be able to look at long-term (week- or month-long) fluctuations of these parameters during O1.

There was apparently some confusion about pausing mechanisms; see alog 21822.  If the scheme referred to there is restored, the PAUSE and ENABLE features will be fully under the control of the operators.  Independently, injections will automatically be paused by the action of the GRB alert code setting the CAL-INJ_EXTTRIG_ALERT_TIME channel.  I have emailed Duncan to try to sort this out.

Last night there were two GRB alerts that paused the injections, and they DID NOT enable Tinj. The Tinj Control went back to Disabled as we had it set to previously. This is good and works as outlined in the HWInjBookkeeping wiki (Thank you Peter Shawhan!). This was my main worry and seems that has already taken care of. It is a bit misleading when the Tinj control goes from Disabled --> Paused and begins to count up to the "Pause Until" time, but after trending the channels it shows that will not enable the Tinj after the times meet.

As I similarly pointed out to the folks at LLO when they tried to implement something similar, having the GRB alert process pause the injection process is a bad model for how to chain the dependencies.  Is the GRB process expecting to unpause the injections as well?  How do you plan on handling this when there are multiple external alert processes trying to pause the injections?  They're all just going to be pausing and un-pausing as they see fit?  Bad plan.

Apparently some confusion about this resurfaced after we had (I thought) resolved it in late August (alog 20013).  Following the original scheme, CAL-INJ_TINJ_PAUSE and CAL-INJ_TINJ_ENABLE are intended to be under the control of the human operator to set or unset.  In parallel, tinj also pauses injections automatically for one hour following the GPS time inserted in CAL-INJ_EXTTRIG_ALERT_TIME by the GRB alert code, ext_alert.py .  I have emailed Duncan to try to sort this out.

THE DROP FROM OBSERVE MODE AT 21:12:30UTC was NOT a change in the IFO, and ALL DATA 19:40UTC to the end of the lock (currently the IFO is still locked) are GOOD!

It appears that the GRB alarm disabled injections, so GWIstat is OK but yellow.  Tj and others are looking into it.

Can you add a plot of the amplitude and phase of 36MHz signal that is common to all four quadrants when there's no misalignment?

As requested, here are plots of the 36MHz signal that is common to all quadrants at the ASWFSA and ASWFSB locations in the simulation. I also checked whether the "sidebands on sidebands" from the series modulation at the EOM had any influence on the signal that shows up here: apparently it does not make a difference beyond the ~100ppm level. 

At Daniel's suggestion, I adjusted the overall WFS phases so that the 36MHz bias signal shows up only in the I-phase channels. This was done just by adding the phase shown in the plots in the previous comment to both I and Q detectors in the simulation. I've attached the ASWFS sensing matrix elements for MICH (BS) and SRC2 (SRM) again here with the new demod phase basis. 

**EDIT** When I reran the code to output the sensitivities to WFS spot position (see below) I also output the MICH (BS) and SRC2 (SRM) DOFs again, as well as all the other ASC DOFs. Motivated by some discussion with Keita about why PIT and YAW looked so different, I checked again how different they were. In the outputs from the re-run, PIT and YAW don't look so different now (see attached files with "phased" suffix, now also including SRC1 (SR2) actuation). The PIT plots are the same as previously, but the YAW plots are different to previous and now agree better with PIT plots.

I suspect that the reason for the earlier difference had something to do with the demod phases not having been adjusted from default for YAW signals, but I wasn't yet able to recreate the error. Another possibility is that I just uploaded old plots with the same names by mistake. 

To clarify the point of adjusting the WFS demod phases like this, I also added four new alignment DOFs corresponding to spot position on WFSA and WFSB, in ptich and yaw directions. This was done by dithering a steering mirror in the path just before each WFS, and double demodulating at the 36MHz frequency (in I and Q) and then at the dither frequency. The attached plots show what you would expect to see: In each DOF the sensitivity to spot position is all in the I quadrature (first-order sensitivity to spot position due to the 36MHz bias). Naturally, WFSA spot position doesn't show up at WFSB and vice versa, and yaw position doesn't show up in the WFS pitch signal and vice versa. 

For completeness, the yaxis is in units of W/rad tilt of the steering mirror that is being dithered. For WFSA the steering mirror is 0.1m from the WFSA location, and for WFSB the steering mirror is 0.2878m from the WFSB location. We can convert the axes to W/mm spot position or similar from this information, or into W/beam_radius using the fact that the beam spot sizes are at 567µm at WFSA and 146µm at WFSB.

As shown above the 36MHz WFS are sensitive in one quadrature to spot position, due to the constant presence of a 36MHz signal at the WFS. This fact, combined with the possibility of poor spot centering on the WFS due to the effects of "junk" carrier light, is a potential cause of badness in the 36MHz AS WFS loops. Daniel and Keita were interested to know if the spot centering could be improved by using some kind of RF QPD that balances either the 18MHz (or 90MHz) RF signals between quadrants to effectively center the 9MHz (or 45MHz) sideband field, instead of the time averaged sum of all fields (DC centering) that is sensitive to junk carrier light. In Daniel's words, you can think of this as kind of an "RF optical lever".

This brought up the question of which sideband field's spot postion at the WFS changes most when either the BS, SR2 or SRM are actuated.

To answer that question, I:

• Added 18MHz and 90MHz "WFS" to the Finesse model.
• Phased these new "WFS" so that all the 18MHz or 90MHz "sum" signals show up in the I-phase (see first two plots).
• Plotted the new "WFS" responses to BS, SR2 and SRM pitch and yaw (normalized by their "sum" signal), as a function of SR3 RoC (see the rest of the plots).

Some observations from the plots:

• 90MHz "WFS" show much more response to SRC1 (SR2) and SRC2 (SRM) tilts than 18MHz "WFS". This is somewhat intuitive, because the 45MHz sidebands are resonant in the SRC and the SRC eigenmode may be more sensitive to SR alignments than a beam traced through "single bounce" style.
• The 90MHz response to SRM/SR2 tilt remain very much in the I phase, with almost no signal in the Q-phase. 
• 18MHz "WFS" show more response to MICH (BS) than the 90MHz "WFS". This is problably because a BS tilt causes a large coupling of 9MHz HG10/01 mode from the PRC to the SRC relative to the amount of 9MHz HG00 mode already in the SRC (due to high Michelson reflectivity + SRC non-resonance for 9MHz HG00). Since I normalize to the total sideband power, this looks like a bigger response in 18MHz than 90MHz.
• The 18MHz response to BS tilt is mostly in the Q phase. I'm not sure exactly how to interpret this, but my naive guess is that it's related to the BS tilt being a "differential" mode tilt for the X and Y arms of the small Michelson.

I looked again at some of the 2f WFS signals, this time with a linear sweep over alignment offsets rather than a dither transfer function. I attached the results here, with detectors being phased to have the constant signal always in I quadrature. As noted before by Daniel, AS18Q looks like a good signal for MICH sensing, as it is pretty insensitive to beam spot position on the WFS. Since I was looking at larger alignment offsets, I included higher-order modes up to order 6 in the calculation, and all length DOFs were locked. This was for zero SR3 RoC offset, so mode matching is optimal.

I've updated the slide I'd made in the PreER7 -era that elucidates all of the time delays and approximations that we've made to come up with the seven 16 [kHz] clock-cycle delay between the actuation path and sensing path. The ER7 version is pg 7 of G1500750. See attached.

In summary, the total delay *between* the inverse sensing and actuation chains, if we approximate all high-frequency frequency response as delays that are in addition to the "true" delays from computer exchanges, if we weren't limited by 16 [kHz] clock cycles should be 442.6 [us]. Because we are limited to 16 [kHz] clock cycles, we've chosen 7, which is a delay of 427.3 [us] -- a 15.3 [us] systematic error.

You should also remember, that having this delay between the chains means that CAL-CS_DELTAL_EXTERNAL has an overall delay or "latency" equivalent to that of the inverse sensing function advance, which is 213.6 [us].

Note that these numbers are LHO-centric -- the approximation for the OMC DCPD signal chain of 40 [us] assumes the pole frequencies of the H1 OMC DCPD chain, and the estimation of the systematic error in phase uses H1's DARM unity gain frequency of 40.65 [Hz]. For LLO, the details should be redone if a precise answer is needed.

Starting around 2015-09-22 17:51:00 Z we had a few minutes or what appeared to be full-on instability of the RFAM stabilization servo. The control signal spectrum was >10× the typical value from 10 to 100 Hz. [Edit: actually, it looks like glitching; see below.]

I tried turning the modulation index down by as much as 1.5 dB, but there was no clear effect.

I've attached time series as a zipped DTT xml for the driver channls (control signal, error signal, OOL sensor) during such a glitchy period.

In the control signal, all the glitches I looked at have the same characteristic shape (see the screenshot with the zoomed time series): an upward spike, a slight decay, a downward spike, and then a slower decay back to the nominal control signal level.

The control signal during the Γ-reduction attempts seems quite smooth; the 0.2-dB steps do not produce glitches.

We tried this out this morning, I turned the filter on at 15:21 , it was on for several hours.  The first screenshot show error and control spectra with the boost on and off.  As you would expect there is a modest increase in the control signal at low frequencies and a bit more supression of the error signal.  The IFO was locked durring maintence activities (including praxair deliveries) so there was a lot of noise in DARM.  I tried on off tests to see if the filter was causing the excess noise, and saw no evidence that it was.  

We didn't get the earthquake I was hoping we would have durring the maintence window, but there was some large ground motion due to activities on site.  The second attached screenshot shows a lockloss when the chilean earthqauke hits (21774), the time when I turned on the boost this morning, and the increased ground motion durring maintence day.  The maintence day ground motion that we rode out with the boost on were 2-3 times higher than the EQ, but not all at the same time in all stations.  

We turned the filter back off before going to observing mode, and Laura is taking a look to see if there was an impact on the glitch rate.  

I took a look at an hour's worth of data after the calibration changes were stable and the filter was on (I sadly can't use much more time) . I also chose a similar time period from this afternoon where things seemed to be running fine without the filter on. Attached are glitchgrams and trigger rate plots for the two periods. The trigger rate plots show data binned in to 5 minute intervals.

When the filter was on we were in active commissioning, so the presence of high SNR triggers are not so surprising. The increased glitch rate around 6 minutes is from Sheila performing some injections. Looking at the trigger rate plots I am mainly looking to see if there is an overall change in the rate of low SNR triggers (i.e. the blue dots) which contribute the majority to the background. In the glitchgram plots I am looking to see if I can see a change of structure.

Based upon the two time periods I have looked at I would estimate the filter does not have a large impact on the background, however I would like more stable time when the filter is on to further confirm.

Check out the attachment to LHO aLOG 21815 for a graphical representation of why seven 16 [kHz] clock-cycles were chosen.

Also in the above email, Peter has *not* included delay for the OMC DCPD signal chain, he has *only* considered extra delay from the AA and AI filtering.

We are looking for the source of the 41 Hz noise lines. 
We used the coherence tool results for a week of ER8, with 1 mHz resolution:
https://ldas-jobs.ligo-wa.caltech.edu/~eric.coughlin/ER7/LineSearch/H1_COH_1123891217_1124582417_SHORT_1_webpage/
and as a guide looked at the structure of the 41 Hz noise, as seen in the PSD posted above by Keith.
Michael Coughlin then ran the tool that plots coherence vs channels, 
https://ldas-jobs.ligo-wa.caltech.edu/~mcoughlin/LineSearch/bokeh_coh/output/output-pcmesh-40_41.png
and made the following observations

Please see below. I would take a look at the MAGs listed, they only seem to be spiking at these frequencies.
The channels that spike just below 40.95:
 H1:SUS-ETMY_L3_MASTER_OUT_UR_DQ
 H1:SUS-ETMY_L3_MASTER_OUT_UL_DQ
 H1:SUS-ETMY_L3_MASTER_OUT_LR_DQ
 H1:SUS-ETMY_L3_MASTER_OUT_LL_DQ
 H1:SUS-ETMY_L2_NOISEMON_UR_DQ
 H1:SUS-ETMY_L2_NOISEMON_UL_DQ
 H1:PEM-CS_MAG_EBAY_SUSRACK_Z_DQ
 H1:PEM-CS_MAG_EBAY_SUSRACK_Y_DQ
 H1:PEM-CS_MAG_EBAY_SUSRACK_X_DQ

The channels that spike just above 41.0 are:

 H1:SUS-ITMY_L2_NOISEMON_UR_DQ
 H1:SUS-ITMY_L2_NOISEMON_UL_DQ
 H1:SUS-ITMY_L2_NOISEMON_LR_DQ
 H1:SUS-ITMY_L2_NOISEMON_LL_DQ
 H1:SUS-ITMX_L2_NOISEMON_UR_DQ
 H1:SUS-ITMX_L2_NOISEMON_UL_DQ
 H1:SUS-ITMX_L2_NOISEMON_LR_DQ
 H1:SUS-ITMX_L2_NOISEMON_LL_DQ
 H1:SUS-ETMY_L3_MASTER_OUT_UR_DQ
 H1:SUS-ETMY_L3_MASTER_OUT_UL_DQ
 H1:SUS-ETMY_L3_MASTER_OUT_LR_DQ
 H1:SUS-ETMY_L3_MASTER_OUT_LL_DQ
 H1:SUS-ETMY_L2_NOISEMON_UR_DQ
 H1:SUS-ETMY_L2_NOISEMON_UL_DQ
 H1:SUS-ETMY_L2_NOISEMON_LR_DQ
 H1:SUS-ETMY_L2_NOISEMON_LL_DQ
 H1:SUS-ETMY_L1_NOISEMON_UR_DQ
 H1:SUS-ETMY_L1_NOISEMON_UL_DQ
 H1:SUS-ETMY_L1_NOISEMON_LR_DQ
 H1:SUS-ETMY_L1_MASTER_OUT_UR_DQ
 H1:SUS-ETMY_L1_MASTER_OUT_UL_DQ
 H1:SUS-ETMY_L1_MASTER_OUT_LR_DQ
 H1:SUS-ETMY_L1_MASTER_OUT_LL_DQ
 H1:SUS-ETMX_L2_NOISEMON_UR_DQ
 H1:SUS-ETMX_L2_NOISEMON_LL_DQ
 H1:PEM-EY_MAG_EBAY_SUSRACK_Z_DQ
 H1:PEM-EY_MAG_EBAY_SUSRACK_Y_DQ
 H1:PEM-EY_MAG_EBAY_SUSRACK_X_DQ
 H1:PEM-CS_MAG_LVEA_OUTPUTOPTICS
 H1:PEM-CS_MAG_LVEA_OUTPUTOPTICS_QUAD_SUM_DQ

The magnetometers do show coherence at the two spikes seen in Keith's plot. The SUS channels are also showing coherence at these frequencies, sometimes broad in structure, sometimes narrow. See the coherence plots below.

Nelson, Michael Coughlin, Eric Coughlin, Pat Meyers
 

Nelson, et. al

Interesting list of channels. Though they seem scattered, I can imagine a scenario where the SRM's highest roll mode frequency is still the culprit. 

All of the following channels you list are the drive signals for DARM. We're currently feeding back the DARM signal to only ETMY. So, any signal your see in the calibrated performance of the instrument, you will see here -- they are part of the DARM loop.
 H1:SUS-ETMY_L3_MASTER_OUT_UR_DQ
 H1:SUS-ETMY_L3_MASTER_OUT_UL_DQ
 H1:SUS-ETMY_L3_MASTER_OUT_LR_DQ
 H1:SUS-ETMY_L3_MASTER_OUT_LL_DQ
 H1:SUS-ETMY_L2_NOISEMON_UR_DQ
 H1:SUS-ETMY_L2_NOISEMON_UL_DQ
 H1:SUS-ETMY_L2_NOISEMON_LR_DQ
 H1:SUS-ETMY_L2_NOISEMON_LL_DQ
 H1:SUS-ETMY_L1_NOISEMON_UR_DQ
 H1:SUS-ETMY_L1_NOISEMON_UL_DQ
 H1:SUS-ETMY_L1_NOISEMON_LR_DQ
 H1:SUS-ETMY_L1_MASTER_OUT_UR_DQ
 H1:SUS-ETMY_L1_MASTER_OUT_UL_DQ
 H1:SUS-ETMY_L1_MASTER_OUT_LR_DQ
 H1:SUS-ETMY_L1_MASTER_OUT_LL_DQ

Further -- though we'd have to test this theory by measuring the coherence between, say the NoiseMon channels and these SUS rack magnetometers, I suspect these magnetometers are just sensing the requested DARM drive control signal
 H1:PEM-EY_MAG_EBAY_SUSRACK_Z_DQ
 H1:PEM-EY_MAG_EBAY_SUSRACK_Y_DQ
 H1:PEM-EY_MAG_EBAY_SUSRACK_X_DQ

Now comes the harder part. Why the are ITMs and corner station magnetometers firing off? The answer: SRCL feed-forward / subtraction from DARM and perhaps even angular control signals. Recall that the QUAD's electronics chains are identical, in construction and probably in emission of magnetic radiation.   
 H1:PEM-CS_MAG_EBAY_SUSRACK_Z_DQ
 H1:PEM-CS_MAG_EBAY_SUSRACK_Y_DQ
 H1:PEM-CS_MAG_EBAY_SUSRACK_X_DQ
sound like they're in the same location for the ITMs as the EY magnetometer for the ETMs. We push SRCL feed-forward to the ITMs, and SRM is involved in SRCL, and also there is residual SRCL to DARM coupling left-over from the imperfect subtraction. That undoubtedly means that the ~41 [Hz] mode of the SRM will show up in DARM, SRCL, the ETMs and the ITMs. Also, since the error signal / IFO light for the arm cavity (DARM, CARM -- SOFT and HARD) angular control DOFs have to pass through HSTSs as they come out of the IFO (namely SRM and SR2 -- the same SUS involved in SRCL motion), they're also potentially exposed to this HSTS resonance. We feed arm cavity ASC control signal to all four test masses.

That would also explain why the coil driver monitor signals show up on your list:
 H1:SUS-ITMY_L2_NOISEMON_UR_DQ
 H1:SUS-ITMY_L2_NOISEMON_UL_DQ
 H1:SUS-ITMY_L2_NOISEMON_LR_DQ
 H1:SUS-ITMY_L2_NOISEMON_LL_DQ
 H1:SUS-ITMX_L2_NOISEMON_UR_DQ
 H1:SUS-ITMX_L2_NOISEMON_UL_DQ
 H1:SUS-ITMX_L2_NOISEMON_LR_DQ
 H1:SUS-ITMX_L2_NOISEMON_LL_DQ

The 41 Hz showing up in
 H1:SUS-ETMX_L2_NOISEMON_UR_DQ
 H1:SUS-ETMX_L2_NOISEMON_LL_DQ
(and not in the L3 or L1 stage) also is supported by the ASC control signal theory -- we only feed ASC to the L2 stage, and there is no LSC (i.e. DARM) request to ETMX (which we *would* spread among the three L3, L2, and L1 stages.). Also note that there's a whole integration issue about how these noise monitor signals are untrustworthy (see Integration Issue #9), and the ETMX noise mons have not been cleared as "OK," and in fact have been called out explicitly for their suspicious behavior in LHO aLOG 17890

I'm not sure where this magnetometer lives:
 H1:PEM-CS_MAG_LVEA_OUTPUTOPTICS
 H1:PEM-CS_MAG_LVEA_OUTPUTOPTICS_QUAD_SUM_DQ
but it's clear from the channel names that these is just two different versions of the same magnetometer.

I'm surprised that other calibrated LSC channels like
H1:CAL-CS_PRCL_DQ
H1:CAL-CS_PRCL_DQ
H1:CAL-CS_PRCL_DQ
don't show up on your list. I'm staring at the running ASD of these channels on the wall and there's a line at 41 [Hz] that in both the reference trace and the current live trace (though, because PRCL, SRCL, and MICH all light that bounces off of HSTSs, I suspect that you might find slightly different frequencies in each).

"I see your blind list of channels that couple, and raise you a plausible coupling mechanism that explains them all. How good is your hand?!"

I neglected to state explicitly that the spectra I posted are taken
from non-overlapped Hann-windowed 30-minute SFTs,
hence with bins 0.5556 mHz wide and BW of about 0.83 mHz.

Attached are close-in zooms of  the bands around 41 Hz peaks,
from the ER8 50-hour data integration, allowing an estimate of 
their Q's (request from Peter F). 

For the peak at about 40.9365 Hz, one has:
FWHM ~ 0.0057 Hz
-> Q = 40.94/.0057 = 7,200

For the peak at about 41.0127 Hz, one has:
FWHM ~ 0.0035 Hz
-> Q = 41.01/0.0035 = 12,000

Also attached are zooms and close-in zooms for the peak at 41.9365 Hz
from 145 hours of ER7 data when the noise floor and the peak were
both higher. The 41.0127-Hz peak is not visible in this data set integration.

In the ER7 data set, one has for 41.9365 Hz:
FWHM ~  0.0049 Hz
-> Q = 40.94/0.0049 = 8,400

Peter expected Q's as high as 4000-5000 and no lower than 2000 for
a triplet suspension. These numbers are high enough to qualify.

Andy Lundgren pointed out that there is a line at about 28.2 Hz that 
might be close enough to 40.9365/sqrt(2) = 28.95 Hz to qualify as
the bounce-mode counterpart to the suspected roll mode.

So I've checked its Q in the 50-hour ER8 set and the 145-hour ER7 set
and am starting to think Andy's suspicion is correct (see attached spectra).
I get Q's of about 9400 for ER and 8600 for ER7, where the line in 
ER7 is much higher than in ER8, mimicking what is seen at 41 Hz.

In an email Gabriele Vajente has stated, "...the noise might be correlated to PRCL." There is a coherence spike between h(t) and H1:LSC-PRCL_OUT_DQ at 40.936 Hz. Here is the coherence for a week in ER8.

Peter F asked if Q of ~ 10,000 for bounce and roll modes was plausible.

Answer is yes. We have evidence that the material loss can at least a factor of 2 better than 2e-4 - e.g. see our paper (due to be published soon in Rev Sci Instrum,) P1400229, where we got an average 1.1 x 10^-4 loss for music wire. Q = 1/loss.

[Stuart A, Jeff K, Norna R]

After having looked through acceptance measurements, taken in-chamber (Phase 3), for all H1 HSTSs, it should be noted that our focus was on the lower frequency modes of the suspensions, so we have little data to refine the estimates of the individual mode frequencies for each suspension.

No vertical (modeV3 at ~27.3201 Hz) or roll (modeR3 at ~40.369 Hz) modes are present in the M1-M1 (top-to-top) stage TFs of the suspensions.

Some hints of modes can be observed in M2-M2 and M3-3 TFs (see attached below), as follows:-

1) M2-M2, all DOFs suffer from poor coherence above 20 Hz. However, there are some high Q features that stand out in the L DOF for SRM, at frequencies of 27.46 Hz and 40.88 Hz. In Pitch, there is a high Q feature at 27.38 Hz for PR2. In Yaw, a feature at 40.81 Hz is just visible for MC1.

2) M3-M3, again all DOFs suffer very poor coherence above 20 Hz. However, a feature can be seen standing above the noise at 26.7 Hz for MC2 in the L DOF. Also, a small peak is present at 40.92 Hz for SR2 in the Yaw DOF.

We currently don't have any bandstops for these modes on the tripples, except for in the top stage length path to SRM and PRM.  It would not impact our ASC loops to add bandstops to the P+Y input on all triples.  We will do this next time we have a chance to put some changes in.  

Ryan Derosa mentioned that he took some low resolution measurements that include an L1 SR2 roll mode at 41.0 Hz.

I have now looked at the data for all the MCs, to complement the PRs and SRs above in log 21741. Screenshots of the data are attached, a list of the modes found are below.

H1

SUS    bounce (Hz)      roll (Hz)

MC1      27.38                40.81

MC2      27.75                40.91

MC3      27.43?              40.84

L1

SUS    bounce (Hz)      roll (Hz)

MC1      27.55?              40.86

MC2        ---                   40.875

MC3      27.53                40.77

Error bars of +- 0.01 Hz.

I am not sure about the bounce modes for H1 MC3 and L1 MC1 since the peaks are pretty small. I couldn't find any data on L1 MC2 showing a bounce mode.

Expanding the channel list to include all channels in the detchar O1 channel list:

https://wiki.ligo.org/DetChar/O1DetCharChannels

I ran a coherence study for a half our of data towards the end of ER8.

I see particularly high coherence at 40.93Hz in many channels in LSC, OMC, ITM suspensions, and also a suspension for PR2. It seems to me like this particularly strong line is probably due to PR2 based on these results, Keith's ASDs, and Brett's measurements, and it seems to be very highly coherent.

Full results with coherence matrices and data used to create them (color = coherence, x axis = frequency, y axis = channels) broken down roughly by subsystem can be found here:

https://ldas-jobs.ligo-wa.caltech.edu/~meyers/coherence_matrices/1126258560-1801/bounce_roll4.html

Attached are several individual coherence spectra that lit up the coherence matrices with the frequency of maximum coherence in that range picked out.

-Pat