I'm posting an early version of this alog so that people can see it, but plan to edit again with the results of the second test. 

Yesterday I took a few minutes to follow up on the meausrements in alog 21869.  This time in addition to driving TMS I drove the ISI in the beam direction to reproduce the motion caused by the backreaction to TMS motion. We also breifly had a chance to move the TMSX angle while exciting L. 

The main conclusions are:

• The motion that produces the noise in DARM while driving TMSX seems more likely to be due to motion of the ISI than motion of TMS.  The smaller, linear coupling from TMSY does seem to be due to transmon motion.
• Driving the ETMX ISI produces a broad peak in DARM, however based on the normal level of GS13 noise in the X direction you would not predict that this noise should not normally dominate DARM at 75 Hz. The same drive at ETMY does not produce any noise in DARM.  To see if this coupling can explain the noise from 77-80 Hz we should make injections at those frequencies (and with white noise) on the ISI in multiple directions to allow comparisons to the ambient motion of the ISI and let us make a projection of how much of our unexplained noise is due to this blinear coupling.
• driving the ETMX ISI in X produces a yaw QPD signal, but no pitch signal.  This seems counter intituive to me, and I wonder if it is a clue about the scattering/clipping or just something I don't understand about how TMS reacts to ISI motion.
• There is a ghost beam near X TRB which has about 0.5% as much power as the main beam.
• The coupling produced by the driven peak at 75 Hz is not very sensitive to changes in the TMS position or angle, although the sidebands on the peak do seem to change as TMS is moved.

Comparison of ISI drive to TMS drive for X and Y

The attached screenshot shows the main results of the first test (driving ISIs and TMSs).  In the top right plot you can see that I got the same amount of ISI motion for 3 cases (driving ETMX ISI, TMSX, ETMY ISI) and that driving TMSY with the same amplitude as TMSX resulted in a 50% smaller motion of the ISI.  Shaking the TMS in the L direction induces a larger motion measured by the GS13s in the direction perpendicular to the beam, than in the beam direction, which was not what I expected.  I chose the drive strength to get the same motion in the beam direction, so I have not reproduced the largest motion of the ISI with this test. If there is a chance it would be interesting to also repeat this measurement reproducing the backreaction in the direction perpendicular to the beam.  

The middle panels of the first screnshot show the motion measured by OSEMs. TMS osems see about a factor of 10 more motion when the TMS is driven than when the ISI is driven.  The signal is also visible in the quad top mass osems, but not lower down the chain.  For the X end, the longitudnal motion seen by the top mass is about a factor of 2 higher when the TMS is excited than when the ISI is excited (middle left panel), which could be because I have not reproduced the full backreaction of the ISI to the TMS motion.  However, it is strange that for ETMY the top mass osem signal produced by driving TMS is almost 2 orders of magnitude larger than the motion produced by moving the ISI. It seems more likely that this is a problem of cross coupling between the osems than real mechanical coupling. The ETMY top mass osems are noisier than ETMX, as andy lundgren pointed out (20675).  It would be interesting to see a transfer function between TMS and the quad top mass to see if this is real mechanical coupling or just cross talk. 

In the bottom left panel of the first screenshot, you can compare the TMS QPD B yaw signals.  The TMS drive produces larger QPD signals than the ISI drive, as you would expect for both end stations.  My first gues would be that driving the ISI in the beam direction could cause TMS pitch, but shouldn't cause as much yaw motion of the TMS.  However, we see the ETMX ISI drive in the yaw QPDs, but not pitch.  The Y ISI drive does not show up in the QPDs at all.  

Lastly, the first plot in the first screenshot shows that the level of noise in DARM produced by driving the ETMX ISI is nearly the same as what is produced by driving TMSX.  Since the TMS motion (seen by TMS osems) is about ten times higher when driving TMS, we can conclude that this coupling is not through TMS motion but the motion of something else that is attached to the ISI. Driving ETMY ISI produces nothing in DARM but driving TMSY produces a narrow peak in DARM. 

For future reference:

I drove ETMX-ISI_ST2_ISO_X_EXC with an amplitude of 0.0283 cnts at 75 Hz from 20:07:47 to 20:10:00UTC sept 29th

I drove 2000 cnts in TMSX test L from 20:10:30 to 20:13:30UTC 

I drove ETMY-ISI_ST2_ISO_Y_EXC with an amplitude of 0.0612 cnts at 75 Hz from 20:13:40 to 20:16:30UTC 

I drove 2000 cnts in TMSY test L from 20:17:10 to 20:20:10UTC

Driving TMSX L while rastering TMS position and angle

I put a 2000 cnt drive on TMSX L from about 2:09 UTC September 30th to 2:37 when I broke the lock. We found a ghost beam that hits QPD B when TMS is misaligned by 100 urad in the positive pitch direction.  There is about 0.5% as much power in this beam as in the main beam (not accounting for the dark offset).  I got another chance to do this this afternoon, and was able to move the beam completely off of the QPDs, which did not make the noise coupling go away or reduce it much.  We can conclude then scatter off of the QPDs is not the main problem.  There were changes in the shape of the peak in DARM as TMS moved, and changes in the noise at 78 Hz (which is normally non stationary) Plots will be added tomorrow.

Speculation

There is a feature in the ETMX top mass osems (especially P and T) around 78 Hz that is vaugely in the right place to be related to the excess noise in the QPDs and DARM. Also, Jeff showed us some B&K measurements from Arnaud (7762) that might hint at a Quad cage resonance at around 78 Hz, although the measured Q looks a little low to explain the spectrum of the TMSX QPDs or the feature in DARM. One could spectulate that the motion driving the noise at 78Hz  is the quad cage resonance, but this is not very solid.  Robert and Anamaria have data from their PEM injections that might be able to shed some light on this.

For the last UTC day (30th Sept 00:00 UTC - 1st Oct 00:00 UTC) the RF45 flag only removed 60 seconds of science data. Since the swap it has only marked 180 seconds of time. This could mean things are better or I need to retrain the flag since the swap, investigating...

Activity Log: All Times in UTC (PT)

15:00 (08:00) Take over from TJ
15:15 (08:15) Jodi – Driving to Sea Container to put things in storage
15:33 (08:33) Jodi – Finished at Sea Container
15:40 (08:40) Richard – Going into Garbing room
17:15 (10:15) LLO called – They are dropping out of Observing to make some improvements 
17:43 (10:43) Set Intent bit to Commissioning – LLO is down Keita going into CRE to work on 45Mhz
17:47 (10:47) Lockloss – Possible EQ activity NOTE: Keita did not make into CRE before lockloss
18:17 (11:17) IFO locked at NOMINAL_LOW_NOISE, 22.5W, 61Mpc
18:18 (11:18) Set the Intent bit to Observing
18:23 (11:23) Set Intent bit to Commissioning 
18:23 (11:23) Sheila – Running some measurements while LLO is recovering from Lockloss
18:36 (11:36) Karen – Swifting in the Mechanical building
18:55 (11:55) Karen - Finished in Mechanical building
19:41 (12:41) Set the Intent bit back to Observing
21:05 (14:05) Filiberto & Manny – Going to Mid-Y to recover parts
21:14 (14:14) Set Intent bit to Commissioning – Jeff K running hardware injections
22:20 (15:20) Lockloss – Unknown
22:48 (15:48) IFO locked at NOMINAL_LOW_NOISE, 22.4W, 70Mpc
22:51 (15:51) Set Intent bit to Observing
23:00 (16:00) Handoff to Travis


	

End of Shift Summary:

Title: 09/30/2015, Day Shift 15:00 – 23:00 (08:00 – 16:00) All times in UTC (PT)

Support: Sheila, Dave B.

Incoming Operator: Travis

Shift Summary: 
- 15:00 IFO locked. Intent Bit = Observing Mode. Wind is calm, no seismic activity. All appears normal.     
- 17:25 (10:25) 5.1 mag EQ in Mexico – Lost lock at 17:47 (10:47). 
-18:00 (11:00) Keita working on 45Mhz modulator during lockloss/recovery.
-18:23 (11:23) Set Intent bit to Commissioning – Jeff K & Sheila running measurements while LLO is down.

    There were two lockloss events today. The IFO recovered and relocked without much difficulty. The range has been good and environmental conditions were quiet (except for the EQ in Mexico) all day. 

 
   

J. Kissel, C. Biwer, S. Karki

We tested using PCAL as a hardware injector. We did 3 injections into the traditional H1:CAL-INJ_TRANSINET_EXC used for hardware injections in the past and 3 into H1:PCALX_SWEPT_SINE_EXC to test using PCAL for hardware injections.

All injections used the 15Hz test waveform from aLog 21838.

The first injection into H1:CAL-INJ_TRANSINET_EXC was successful. The command line was:
 awgstream H1:CAL-INJ_TRANSIENT_EXC 16384 coherenttest1from15hz_1126257408.out 1.0 -d -d >> 2015-09-30_PCALInjTest_DARMCTRLEXC.txt

We then tried an injection into H1:PCALX_SWEPT_SINE_EXC but it was unsuccessful because the injection channel list for the hinj account was restricted and did not include this channel. The command line was:
 awgstream H1:CAL-PCALX_SWEPT_SINE_EXC 16384 coherenttest1from15hz_1126257408.out 1.0 -d -d >> 2015-09-30_PCALInjTest_PCALINJ.txt

D. Barker added H1:PCALX_SWEPT_SINE_EXC to the allowed excitation channels list for the hinj account and we had a successful set of injections:
 awgstream H1:CAL-PCALX_SWEPT_SINE_EXC 16384 coherenttest1from15hz_1126257408.out 1.0 -d -d >> 2015-09-30_PCALInjTest_PCALINJ.txt
 awgstream H1:CAL-PCALX_SWEPT_SINE_EXC 16384 coherenttest1from15hz_1126257408.out 1.0 -d -d >> 2015-09-30_PCALInjTest_PCALINJ_Trial2.txt
 awgstream H1:CAL-PCALX_SWEPT_SINE_EXC 16384 coherenttest1from15hz_1126257408.out 1.0 -d -d >> 2015-09-30_PCALInjTest_PCALINJ_Trial3.txt
 awgstream H1:CAL-INJ_TRANSIENT_EXC 16384 coherenttest1from15hz_1126257408.out 1.0 -d -d >> 2015-09-30_PCALInjTest_DARMCTRLEXC_Trial2.txt

We then tried another injection but NDS happened to fail as we tried the injection and the injection was unsuccessful:
 awgstream H1:CAL-INJ_TRANSIENT_EXC 16384 coherenttest1from15hz_1126257408.out 1.0 -d -d >> 2015-09-30_PCALInjTest_DARMCTRLEXC_Trial3.txt

The problem was quickly fixed and we set up to retry the injection. It was successful:
 awgstream H1:CAL-INJ_TRANSIENT_EXC 16384 coherenttest1from15hz_1126257408.out 1.0 -d -d >> 2015-09-30_PCALInjTest_DARMCTRLEXC_Trial4.txt

The logs are attached.

The end times of the injections should be:
DARM 1             1127683334.985681295
PCAL 1              1127683905.985681295
PCAL 2              1127684170.985681295
PCAL 3              1127684464.985681295
DARM 2             1127684765.985681295
DARM 3             1127685142.985681295

As we were doing the injections we made omega scans, they can be found in aLog 22123.

C. Biwer, J. Kissel

Taking advantange of single IFO time to run PCAL vs DARM hardware injections. More details later.

C. Biwer, J. Kissel

Taking advantange of single IFO time to run PCAL vs DARM hardware injections. More details later.

Tuesday 29 September 2015 John and Gately replaced the vibration isolators on end instrument air compressors. So here I follow up the correlation between the glitches and the EX_SEIS_VEA_FLOOR_[X,Y,Z]_DQ commented by Joshua (21470). I have analyzed data from the 09/29 10.00 UTC before the repair and the glitches are totally visible. The data after the repair 09/30 10.00 UTC shows no trace of the glitches. I attach two images to show these.

Now that we've cleaned up all of our systematics from the DARM model and released the O1 version (see LHO aLOG 22056, I've updated the diagram that explains how the actuation path clock cycle delay is derived, and also shows that the current value of 7 [clock cycles] or 427.3 [us] that was recently installed at both sites (LHO aLOG 21788) still does a fine job at approximating the total delay between the inverse sensing and actuation chains.

[Aidan, Alastair]

We ran a calculation of the coupling of intensity noise to displacement noise for the CO2X laser at LHO. The details are as follows:

"The absolute coupling is very low right now due to the small amount of power being used to heat the test masses. The transfer function has not been directly measured but we have an estimate for it in the following document:

When DTT gets data from NDS2, it apparently gets the wrong sample rate if the sample rate has changed. The plot shows the result. Notice that the 60 Hz magnetic peak appears at 30 Hz in the NDS2 data displayed with DTT. This is because the sample rate was changed from 4 to 8k last February.  Keita pointed out discrepancies between his periscope data and Peter F's. The plot shows that the periscope signal, whose rate was also changed, has the same problem, which may explain the discrepancy if one person was looking at NDS and the other at NDS2. The plot shows data from the CIT NDS2. Anamaria tried this comparison for the LLO data and the LLO NDS2 and found the same type of problem. But the LHO NDS2 just crashes with a Test timed-out message.

Robert, Anamaria, Dave, Jonathan

I think it's possible that we're closer to the Newtonian gravitational noise limit than I had thought.  This is on the list of "things we knew were coming, but are perhaps here sooner than I thought they would be". 

The punch line is that we may be limited by Newtonian noise between 16-20 Hz.  Not a wide band, but reasonably consistent with the expectations from papers such as P1200017.

In the attached plot, the blue trace is the calibrated DARM spectrum (CAL-DELTAL_EXTERNAL_DQ) that we show on the wall, taken yesterday.  The green trace is my estimate of the Newtonian noise. 

For the Newtonian noise, I have taken the Z-axis STS-2 seismometer data from the sensors on the ground near each test mass.  (There is one seismometer at each end station, and one in the vertex near the ITMs - I use the same seismometer data for each ITM). The seismometers are in velocity units (I believe Jim said it's nm/s), so I pwelch to get velocity/rtHz, then apply the calibration zpk([],0, 1.6e-10) to get to meters/rtHz.  I then translate to acceleration due to Newtonian noise using eq 1 from T1100237.  Finaly, I add the 4 acceleration contributions (one from each test mass) incoherently and get to displacement by dividing the spectrum by (2*pi*f)^2. 

The Newtonian noise is touching the DARM spectrum between about 16 - 20 Hz. We're within about an order of magnitude in the band 10 - 30 Hz.  Evan will shortly re-run his noise budget code using this "measured" Newtonian noise to see if it helps explain some of the discrepancy between the measured and expected DARM spectra (this spectra is higher than the GWINC curve that is currently used in the noise budget). 

Notably, this estimate of seismically-induced Newtonian noise is somewhat larger than what we've quoted in P1200017 and T1100237.  If I use only the ETMY spectrum as an estimate for all 4 test masses, I get an answer more consistent with our past estimates.  However, using the actual seismic signals from each test mass, I'm getting this slightly higher estimate. 

The script to generate this plot is attached, as is the exported-from-DTT text file of the calibrated DARM spectrum.

Summary

Attached is the dark noise of REFL9Q, along with an estimate of the shot noise and a conversion of these noises into equivalent frequency noise in CARM.

The dark noise appears to be slightly below the shot noise level.

Details

I took the TNC that goes directly into the common-mode board and put it into an SR785. Also attached is the noise with the input of the SR785 terminated.

I also have tried to estimate how this compares to the shot noise on the diode. In full lock at 24 W, we see 3.6 mW of dc light on the PD (according to the calibrated REFL_A_LF channel). Off resonance and at 2.0 W, we have 13.6 mW of dc light. So the CARM visibility is about 98%.

The shot noise ASD (in W/rtHz) and the CARM optical plant (in W/Hz) are both given in Sigg's frequency response document. With a modulation index of 0.22 rad and an incident power of 24 W, the shot noise is 9.4×10⁻¹⁰ W/rtHz, the CARM optical gain is 11 W/Hz, and the CARM pole is 0.36 Hz. [Edit: I was missing some HAM1 attentuation when first calculating the shot noise level. Out of lock, the amount of power on REFL A should be 24 W × 0.1 × 0.5 × 0.5 × 0.5 = 300 mW. That gives a predicted shot noise level of 7.7×10⁻¹¹ W/rtHz, assuming a sideband amplitude reflectivity of 0.44. On the other hand, from the measured in-lock power we can calulate 2(hνP)^1/2 = 5.2×10⁻¹¹ W/rtHz for P = 3.6 mW. This includes the factor of sqrt(2) from the frequency folding but does not include the slight cyclostationary enhancement in the noise from the sidebands (although this latter effect is not enough to explain the discrepancy).] Additionally, I use Kiwamu's measurement of overall REFL9 response (4.7×10⁶ ct/W) in order to get the conversion from optical rf beat note power into demodulated voltage (2900 V/W). These numbers are enough to convert the demodulated dark noise of REFL9Q (and the shot noise) into an equivalent frequency noise. At 1 kHz, the shot noise is about 10 nHz/rtHz; as a phase noise this is 10 prad/rtHz (which is smaller than Stefan's estimate of 80 prad/rtHz). The dark noise, meanwhile, is about 5 nHz/rtHz.