Summary: Coupling of ambient sound is predicted to approach the DARM noise floor below 100 Hz and in the ISI-transmission bands of 350-550 and 850-1000 Hz. Twice the ambient vibration level causes a peak to appear in DARM in the 850-1000 Hz band. At several times background, injections produce nonlinear intermodulation effects, possibly with the OMC length dither, causing DARM peaks in the 100-200 Hz region and at much higher frequencies. The coupling in the 850-1000 Hz band depends on table motion, not vacuum enclosure motion.

I began studying acoustic coupling in the LVEA using the standard iLIGO LVEA injection (speaker in the X-arm of the LVEA, far from interferometer parts except the ITMX optical lever) and immediately noticed strong features in the 850-1000 Hz ISI-resonance band that suggested up-conversion. I then began injecting in narrow bands to study coupling; Figure 1 shows the up and down conversion produced by injections in the 850-1000 Hz band. The 500-700 Hz injection in blue produced only features in that band of DARM. But the red injection, 850-1000 Hz produced features in DARM near 100 Hz and in the region of the first harmonic around 1800, in the region around 2400 Hz, and near 4200 Hz.

Predicted noise from acoustic background

Figure 2 shows the estimated noise floor for ambient acoustic levels. It relies on the assumption of linearity, that is, that 10x the ambient sound will produce 10x the effect in DARM. Linearity is clearly not met in the 850-1000 Hz band. However, Figure 2 is made from 6 narrow injection bands (such as in Figure 1), at 10 to 100 times background sound pressure levels, and, except for the 850-1000 Hz band, none of the other bands showed evidence of non-linear coupling. The predicted ambient noise level for the 850-1000 Hz band is better estimated for the shaker injections below. The predicted ambient points have a wide spread mainly because the microphone is not exactly at the coupling site and, for example, at certain frequencies, the microphone may be at a node or antinode while the coupling site is not. More focused coupling measurements can be more precise. All LVEA beam diverters were closed for acoustic injections except the REFL port.

Figure 2 shows three bands where the predicted ambient noise approaches the noise floor: below 100 Hz, in the 350-550 Hz band, and the 800-1000 Hz band. The later two are familiar ISI transmission bands, which suggest that the coupling is at HAMs. I have not yet measured acoustic coupling at higher frequencies than 1100 Hz because I was not able to make the sound loud enough over a wide band (generally the coupling is low), but it is likely that there is significant coupling at specific higher frequencies because it was observed in shaker injections at HAM6.

Shaking at HAM6 (which excites only locally in contrast with the previous acoustic injections) confirmed that coupling at HAM6 could account for the acoustic coupling in the 850-1000 Hz band, though it doesn’t eliminate the possibility that there is comparable coupling at other sites. To make these HAM6 measurements I mounted a shaker on a blanked off door port and another on a blue cross beam.

DARM amplitude depends on table motion not vacuum enclosure motion

I compared the response of DARM for shaking of the vacuum enclosure (which is a candidate reflector of scattered light), and for shaking of the blue cross beam, which doesn’t shake the vacuum enclosure much but does couple well to table vibrations. Figure 3 shows that, in order to produce a peak in DARM as large as the one I produced by shaking the blue cross beam, I had to shake the vacuum enclosure so that it moved ten times as much as it moved during the cross beam injection. While the enclosure motion varied by 10, the table motion indicated by the GS13 signal was about the same for both injections. This suggests that , in the 850-1000 Hz band, the important motion is the table motion not the vacuum enclosure motion.

Increasing HAM6 table motion to twice ambient produces features in DARM

Figure 4 shows that increases in table motion of two times ambient background (black = ambient), in the 700-900 Hz band, produce features visible in DARM, and non-linear effects become obvious at 5-10 times ambient.

Non linear effects in DARM at higher frequencies and the OMC length dither

Shaker injections at higher frequencies also make peaks, e.g. a 2875 injection produces a peak in DARM at that frequency and another peak at 1220. To demonstrate the nonlinear effects, I injected a slowly swept sine with a shaker on a blue cross beam, and made a video of the DARM spectrum:  http://youtu.be/t6zlUlckuEI  I apologize for shooting video of the control room screen; we don’t yet have software that makes a movie from sequential screen shots, though it is available and might be useful for operator training videos as well as projects like this. 

It is hard to imagine mechanical nonlinearities that could account for these observations, but if the excited motion modulated the beam, I could imagine intermodulations. One possibility, based on the video, is that mechanical oscillations that modulate the beam could be intermodulating with the OMC length dither. Notice in the video that upward and downward travelling peaks are centered on the peak at 4100 Hz (or its sub-harmonic at 2050). The 4100 Hz peak is from the OMC length dither.

Robert

Jeff, Richard, Jim, Dave

WP 5205,5207

Today we performed the following upgrades at EX:

• Install the 18bit DAC cards with the upgraded firmware into h1susex
• Install the new DC power supplies into the IO Chassis for h1susex, h1seiex, h1iscex and h1susauxex
• Program the IO Chassis timing slaves with firmware version 100 for all four chassis

One of the new 18bit DACs caused problems when starting h1susex. At the point where the autocal should have completed, the front end computer froze up. We identifified the bad unit and replaced it with another new card which resolved the problem. The potentially bad card has S/N 101208-59 and was returned to the corner station for DTS testing.

The interface board on h1seiex had a connector issue when the old DC power supply was disconnected. We exchanged it with the I/F board from the DTS x1sush34 unit (a tried and tested board).

The DAC card layout in h1susex did not provide enough room for the new DC power supply. We shifted the DAC cards to the left (as seen from front of unit), and while diagnosing other issues moved all DACs to higher slot numbers than the one ADC card. We may undo this and keep the DACs in a block of five.

here is the current card layout for h1susex:

Where: U=unused, nu=not used, BIO=64,64 Binary IO, E=Empty, bio=16,16 Binary IO, PWR=new DC power supply

We also experienced startup issues with the Dolphin network. We tried power cycling the switch, but restarting the Dolphin manager and then restarting the front ends resolved the issue.

We had to start_streamers on the Dolphin machines as well to sync up the DAQ.

At this point in time all is running at EX, the only problem is h1seiex has a run away IRIG-B which may take several hours to come back down.

Jeff activated the HEPI, ISI and SUS systems at EX, all is operational.

AA AI chassis swap will continue tomorrow morning. We are currently working on PSL, so not all chassis are connected or powered on.

Today started off with VEAs being transitioned to Laser Safe and many activities beginning with the AA/AI Chassis swap being the prime activity.

• 7:00 Cris/Karen cleaning
• 7:55 Turning off ALS lasers (Richard/Peter)
• 8:45amPowered off TCS CO2 Lasers via medm (Peter turned key on power supply)
• 10am:  ISCT EX Access System Sensors (Ken)
• 10:20:  EX HEPI Pump station started alarming.  Looks like it's noise from a poorly grounded Sensor (noted by Hugh).
• 10:30 A Bing Car (with camera on roof) zipped around the LSB/Front Gate (attached)
• 10:33-11:01 Jodi sealing up 3IFO containers.
• 11:17 Travis running hardware to AA/AI crew at end stations
• 11:25 Tomorrow tour prep in LVEA (Hugh)
• ISS instable, RefSignal moved from -1.95 to -1.93.
• Jim/Richard - shutting down EX, so offline - went offline before we could complete the change to SAFE/OFFLINE.  Cheryl set Guardian to request SAFE/OFFLINE for SUS and SEI.
• Filiberto called - we changed all corner station and EY SUS and SEI to SAFE/OFFLINE, EY may not have been necessary for today, but with everything else down, it made sense to do EY also.
• 1:30-3:30 Jeff checking garb at all VEAs
• 3pm Mid-stations were getting warm (received FMCS alarms), so Bubba turned on the Air Handlers.
• 3:05:  Bubba off to EX Lab room to check on HVAC unit
• 3:11-3:30 Jodi in LVEA for 3IFO again
• 3:30 CDS crew came to take a break from EX work, but will be heading back out to continue working on power supply stuff.
• 3:20 AA/AI crew continue work in H1 Elec Room & are now working on PSL (Filiberto, Richard, et. al)
•  

Peter F, Kiwamu,

We looked into the DARM cavity pole tracker signals from the 13 hrs lock stretch from this weekend (alog 18489). Here are summary points:

• The DARM cavity pole showed a long-term drift (on a time scale of 13 hours). The frequency degraded from 350-ish Hz to 328-ish Hz.
• We did not find a high coherence between the cavity pole tracker signals and the following channels:
  • SUS_SRM_M1_LOCK_P(Y)
  • SUS_SRM_M3_WIT_PIT(YAW)
  • SUS_SR2_M1_LOCK_P(Y)
  • SUS_SR2_M3_WIT_PIT(YAW)
  • SUS_BS_M1_LOCK_P(Y)
  • TCS-ITMX_HWS_PROBE_SPHERICAL_POWER
  • OMCR
  • TRX and TRY
• No idea what caused the change in the DARM cavity pole.

[DARM cavity pole tracker signals]

The plots below are the results from the cavity pole tracker:

In both plots, the long stretch started at t = 9.5 hours or so and died at the very end of the plots. The first plot shows the cavity pole location as a function of the time. In addition to the raw data, I also plot a moving-averaged version of the cavity pole location. The movng average currently avarages with 360 data points or for 6 minutes to smooth them out. The same moving-average was applied to the optical gain as well for visiualization purpose.

As shown in the first plot, the DARM cavity pole tends to start from a frequency as high as 350 Hz at the beginning of every lock stretch and then sink down to about 340 Hz after an hour or so. This probably is thermal transient of ITM substrates on the local beam area. Also there clearly is slow drift in the cavity pole which resulted in a low DARM cavity pole frequency of about 328 Hz at the very end of the long lock stretch. According to Elli, the test masses reach the equilibrium point on a time scael of 6 hours, where the heat absorbed from the laser light equilibrate with the entire thermal bath including the chambers and etc. But, since the cavity pole kept drifting for more than 6 hours, it is not clear if we can conclude that this is the thermal lensing. On the other hand, the DARM optical gain increased in the longest lock stretch on the same time scale as the stretch itself. It increased by 1 or 2 %. Since the arm power also slowly increased by roughly 1 %, this may be just an indication of the change in the arm power (and perhaps also degradation in the signal-recycling gain).

[Searching for coherence]

One test we came up with was to take coherence between the cavity pole tracker signals (LOCKIN_I and LOCKIN_Q output signals) and various channgles in order to identify what channels contributed to the cavity pole frequency most. Since we knew that the alignment of SRC was important (alog 18436), we looked into the ASC feedback signals of SRM, SR2 and BS on their top stages,  witness sensors or oplev of SRM, SR2 and SR3 and OMCR as listed in the very top of this alog entry. In addition, since the ITMX Hardtman wavefront sensor was active during this period, we searched for the coherence with it as well.

However, we did not find a high coherence from any of these channels. We used diaggui and picked a time which was roughly in the middle of the stretch. We did a Fourier analysis down to 1 mHz with a number of average of 20. I attach second trends of some relevant channels. Notably we clearly see slow drift in the ITMX HWS by roughly 6x10^-6 [1/m] (there was a secret calibration fact of 0.00326 [1/m/counts]), but this was not coherent with the tracker signals. We also found a slow drift in OMCR which increased by roughly 2%, but no coherence either.

Josh Smith, TJ Massinger, Andy Lundgren, Laura Nuttall

We've taken a look at the ~8h lock stretch on 15th May where the intent bit was active. We've specifically looked for evidence of DAC (for example 17555) and whistle (17452) glitches which have been present in the past. We find no sign of whistles glitches correlated with IMC-F (could be other sources but we haven't seen any yet) and we also find no evidence of DAC glitches. 

The glitch rate for this lock is some of the best we have seen for aLIGO (at either site). Attached is the glitch rate plot for the 15th, which shows the glitch rate to slowly decrease throughout the lock. We'll continue to investigate this lock.

A snapshot of the IFO alignment, in case it is useful later.

Full room (with visitors for Dedication tomorrow and AA/AI work this week)

Subsystem Summaries

• SEI:  Mostly offline due to AA/AI work. 
• SUS:  Model work during AA/AI work.
• CDS:  Lots summarized here:  AA/AI chasis work in corner stations.  VEAs transistioned safe.  Lasers shuttered and/or turned off.  Access Control door sensors on tables.  Timing system work as well.  Hope to be done by Wed, but have until Thurs at noon officially.
• Facilities:  touch up on site, beam tube ongoing
• VAC:   Ion gun work by Rai?
• PSL/PCal/Oplev:  Might take the PSL down during the AA/AI work.  Possible investigations into trips may continue
• Commissioning:  AI chasis measurements,

Tent set-up for lunch tomorrow

Additional NOTES: 

• Don't push the Control Room Conference Table toward the door (for safety/fire alarm reasons)
• No Commissioning Meeting

J. Kissel

Robert has left the site, and I have to head out. After the long stretch's lock loss, I needed to tweak the ETMY alignment by ~0.5 [urad] before the green WFS were able to take over. Other than that, the lock acquisition system has taken over and run with it. So far there have been two failed attempts in the same way -- it gets all the way up to the middle of the power increase (right as the CSOFT and DSOFT loops come on) and then it looses lock. Maybe the ITM OL damping loops need to be off for the lock acquisition sequence and then turned on later? Dunno.

The IFO disappears for a few days starting tomorrow. Lots of electronics need swapping. Hopefully it will be quick to return to this great Sunday's kind of locking around Thursday or Friday.

J. Kissel, R. Schofield

I'm not exactly sure when Evan left last night, but this 23 [W] lock stretch has lasted for 13+ hours thus far (guardian says the lock stretch reached ful LSC_FF at 08:50:27 UTC, which concurs with the arm cavity power -- see attached). Regrettably, Evan didn't hit the Undisturbed bit, but we should consider almost all of the hours this lock stretch entirely undisturbed until Robert goes in. At worst, the landscaping crew had been driving near the building. We've had no substantial Earthquakes, and the wind has stayed around 10 [mph].

He's delaying as long as he can, but Robert has to pack up his HAM6 shaker set up eventually, so that will likely be the cause of the lockloss if the Earth doesn't do it for us. 

C'mon galactic supernova!!

P.S. @DetChar and @CDS -- we REALLY need a way to trend the inspiral range in the control room (that doesn't require matlab or python). Sooner or later, we're going to compute the range in the front end (like LLO already does) if not!

I did some broadband intensity noise injections from about 05:04:00Z to 05:32:00Z, 2015-05-17. I also took another frequency noise coupling TF. Noise projections forthcoming.

I widened the BS violin stopband filter (FM5 in BS M2 LOCK L, 80 dB elliptic). In the course of doing MICH noise injections, I saw a wide response around the beamsplitter violin mode, as was seen at LLO (see Brett's post and the posts linked therein for a discussion). The stopband used to go from 297 Hz to 307 Hz; now it goes from 250 Hz to 350 Hz. These injections seem to indicate that the beamsplitter roll mode is also quite wide, but since this is so close to the UGF of the MICH loop I left the bandstop filter alone.

I took OLTF measurements of PRCL, MICH, and SRCL. PRCL UGF is about 45 Hz and SRCL UGF is about 25 Hz. The MICH UGF was about 12 Hz, with 12 degrees of phase (!). It seems the compensation filter from a few weeks ago is no longer necessary in the full, low-noise 23 W configuration. I'm not sure whether it's necessary at some earlier point in the locking sequence, so I've left it in the guardian for now.

We have seen for a while now that when we transition control of DARM from rf to dc readout, the fluctuations in OMC DC can be as bad as 30% pkpk. We've also seen that the interferometer sometimes loses lock either on the transition step, or on the subsequent step of switching actuators from ETMX to ETMY. For the record, one can do the final DARM stabilization steps (bringing the UGF up to 50 Hz, and engaging the boost) before transitioning to dc readout. This reduces the RIN in OMC DC to less than 10% pkpk. Then, in order to switch actuators, ramp the drive of ETMY ESD on simultaneously while ramping the drive of ETMX ESD down. I used a 30 s ramp, but I suspect we could get away with 10 s or less. I have not put this in the guardian.

I have seen the same 0.4 Hz oscillations in full lock, as Jeff reported earlier. To get around this tonight, I left the ITM oplev damping on. Removing the damping even in full lock leads to instability.

J. Kissel 

The message: I tried to improve the Bounce mode damping, I've installed some new filters; no change in the amount of damping for the bounce modes, and they haven't been cooled any more than when I got started. I've made no changes the guardian code, so in the next lock stretch my work will be erased / cleaned up (except for the new filters), and what used to be turned on turned on before today will be turned on again.

After spending an hour or so trying to get better results out of the installed bounce mode damping filters to no avail, I tried installing much more narrow band-pass filters. I did this because of Shiela's entry (LHO aLOG 18440) seemed to indicate we know the frequencies really well, and I could see what I thought was ETMX at 9.77 [Hz] interacting with what I thought was ITMX at 9.83 [Hz]. However, I found after exploring the parameter space (with gains and +/- 30 or 60 [deg] filters) with the more narrow filters, the situation got more confusing because the top mass of ETMY, ETMX, and ITMX would come in and out of showing 9.83 [Hz]. See for example the attached .pdf of the top mass vertical OSEMs for each. Yuck! After a while I convinced myself that having both IX and EX using the narrow band bp9.7-9.8 (in FM10 of IX and FM5 in EX) with a small gain of +0.1 and +0.05 and their normal -60 [deg] and +60 [deg] filters wasn't making it worse, but I couldn't get any improvement.

This mode interaction are stable / non-existent at low power, but as soon as we elevate to 23 [W], the MICH oscillation creeps in mentioned earlier today (LHO aLOG 18478) creeps in and breaks the lock.

J. Kissel

I've processed the DARM OLG TFs from Thursday (see 18443), and found that the DARM Coupled Cavity Pole Frequency seems relatively stable at 350 +/- 10 [Hz] with respect to IFO power. Admittedly, the data at 23 [W] is only over a small frequency range and is varying by ~5% (even though, as usual, I applied at 0.99% coherence threshold cut on the data points), so that's why I put a +/- 10 [Hz] on the number I quote. I think we'll either have to (a) get more DARM sweeps, (b) use Kiwamu's LSC DCCP tracker, and/or (b) get the PCAL demodulation up and running to check it this is consistent from lock-stretch to lock stretch.

The ITMs are under control for all of these data sets, and the SRC1 yaw loop is tuned as described in LHO aLOG 18442 for the latter three. For all four measurements SRCL to DARM subtraction, ("FF") was off.

Just posting data that Fabrice had requested for a talk. The setup: I wanted to measure the performance of sensor correction on ETMX. I turned off the feed forward (which I've seen add some noise at .5hz, not much, but I've been meaning to investigate) and got .001 bw measurments with the sensor correction on and off. The ISI was fully isolated, with 45mhz blends in Y and 90mhz blends in X. On the first 3 spectra (X,Y &Z) black (ground),orange(st1 t240's) and red(st2 gs13's) are sensor correction on, brown (ground), blue (st1 t240's) and grey (st2 gs13's) are sensor correction off. In X&Y, we are using Ryan's .5hz notch sensor correction on the ISI and in Z we are using RichM's broadband low frequency sensor correction on hepi (fourth & fifth plots).

the remaining roll modes are at 13.89 and 13.98 Hz, but we don't know which is from ETMX and which is from ITMX

This is a follow up entry of LHO ALOG 17601.

A couple of days ago, the discrepancy of the response for DCPDA and DCPDB were found. This was basically caused by misadjusted filter modules for the anti-whitening filters. Some of them were using design values (like Z10:P1) and some others were just left as they had been imported from the LLO setup.

In order to correctly take the whitening transfer functions into account, the wiring of the in-vacuum and in-air connections were necessary to be tracked down. The 1st attachment shows the sufficiently detailed wiring chain for this task. Using the test data (links indicated in the diagram), we can reconstruct what the correct anti-whitening filters should be. The summary can be found below.

[Trivia for Rich: DCPD1 (Transmission side of the OMC BS) is connected to HEAD2, and DCPD2 (Relfection side of the OMC BS) is connected to HEAD1. This is because of twisted D1300369. This cable has J2 for HEAD2 and J3 for HEAD1. This twist exists in LLO and LHO consistently, as far as I know]

=======
Characteristics of the DCPD electronics chain
Complex poles/zeros are expressed by f0 and Q

DCPD A
(DCPD at the transmission side of the OMC DCPD BS)
- Preamp D060572 SN005
Transimpedance: Z_LO = 100.2, Z_HI = 400.0
Voltage amplification ZPK: zeros: 7.094, 7.094, (204.44 k, 0.426), poles: 73.131, 83.167, 13.71k, 17.80k, gain: 1.984

- Whitening filter D1002559 S1101603
(This document defines the gain not at the DC but at a high frequency. The gain below is defined as a DC gain.)
CH5 Whitening
Filter 1: zero 0.87, pole 10.07, DC gain 10.36/(10.07/0.87)
Filter 2: zero 0.88, pole 10.15, DC gain 10.36/(10.15/0.88)
Filter 3: zero 0.88, pole 10.20, DC gain 10.36/(10.20/0.88)
Gain: “0dB”: -0.051dB (nominal), “3dB”: 2.944dB, “6dB”: 5.963dB, “12dB”: 11.84dB, “24dB”: 24.04dB

DCPD B
(DCPD at the reflection side of the OMC DCPD BS)
- Preamp D060572 SN004
Transimpedance: Z_LO = 100.8, Z_HI = 400.9
Voltage amplification ZPK: zeros: 7.689, 7.689, (203.90 k, 0.429), poles: 78.912, 90.642, 13.69k, 17.80k, gain: 1.983

- Whitening filter D1002559 S1101603
CH6 Whitening
Filter 1: zero 0.88, pole 10.13, DC gain 10.41/(10.13/0.88)
Filter 2: zero 0.87, pole   9.96, DC gain 10.40/(  9.96/0.87)
Filter 3: zero 0.88, pole 10.15, DC gain 10.41/(10.15/0.88)
Gain: “0dB”: -0.012dB (nominal), “3dB”: 2.982dB, “6dB”: 6.007dB, “12dB”: 11.87dB, “24dB”: 24.04dB

=======

Now we put these transfer functions into the model and check if we can reproduce the observed relative difference (Attachment 2). In deed, the measurement is well explained by the model below 30Hz where the measurement S/N was good. As we saw in the previous entry, the difference of the DCPDA and DCPDB after the whtening compensation is 20% max. Note that further inspection revealed that this 20% difference is, in fact, mostly coming from the difference of the preamp transfer functions rather than the miscompensation.

So this was the relative calibration between DCPDA and DCPDB. How is the compensation performance of each one? The 3rd attachment shows how much of current we get at the output as H1:OMC-DCPD_A_OUT, H1:OMC-DCPD_B_OUT, and H1:OMC-DCPD_SUM_OUT, if we give 1mA of photocurrent to DCPD_A, DCPD_B, or both (half and half). Ideally, this should be the unity. The plot shows how they have not been adjusted. For the our main GW channel we take sum of two DCPDs. The individual deviations were averaged and thus the sum channel has max 10% deviation from the ideal compensation. This shows up in the GW channel.

=======

So let’s implement correct compensation. Basically we can place the inverse filter of the each filters. The preamplifier, however, includes some poles and zeros whose frequency are higher than the nyquist frequency. Here we just ignore them and assess how the impact is.

The result is shown as the 4th attachment. Upto 1kHz, the gain error is less than 1%. This increases to 5% above 3kHz.  The phase error is 7deg at 1kHz. This increases to 20deg above 3kHz. These are the effect of the ignored pole/zeros. Note that these are static error. In fact, the phase error is quite linear to the frequency. Thus this behaves as a time delay of ~18.5us. Since the phase delay at 100Hz is small, the impact to the DARM feedback servo is minimal. For the feedforward subtraction, however, this might cause some limitation of the subtraction performance. In practice, we measure the coupling transfer function in order to adjust the subtraction, in any case. Therefore this delay would not be a serious problem.

The filter bank to implement the new compensation was already configured. The filter file is attached as foton_DCPDfilters.txt.