Below are trends from the past 10 days

As reported in last night entry, we tried to improve the SRCL noise coupling non stationarity by increasing the low frequency gain of the DHARD Yaw loop. In my initial elog entry, I pointed out that the SRCL coupling was fluctuating following ASC-AS_A_RF45_I_YAW_OUT. However, it turned out that this signal is basically equal to the DHARD yaw error signal. Most of the SRCL coupling fluctuations and residual motion of DHARD are at frequencies below 200 mHz, so I designed a boost to increase the low frequency gain of the loop. The improvement is visible in the first attachment (green without boost, red with boost). The loop accuracy improved significantly, as shown in the second sttachment, which is a time series of the error signal.

With this new loop, Evan injected some SRCL noise and I could do the same analysis I did yesterday to study the SRCL coupling non stationarity. Here are my main comments:

• contrarily to what stated in last night entry, the SRCL coupling is both lower and more stationary. The third attachment shows the SRCL coupling gain (average of the TF in the 100 Hz region) as a function of time. It is on average about 3.5e-11 and fluctuating by some 2e-11. Before DHARD boosting, the coupling was fluctuating between -10e-11 and +27e-11.
• Now the channel ranking gives a different answer: SRCL coupling is mostly modulated like ASC-AS_A_RF36_Q_PIT, and only partially as DHARD YAW. So it seems that we removed most of the fluctuations caused by DHARD, but now we have some other loops to improve. If I'm not mistaken, AS36 signals should be used to control some SRC degree of freedoms

This morning after some full lock attempts, the IMC was found to be so misaligned that it did not lock any more. It turned out that this was due to the integrators in IMCASC which kept integrating the intentional offsets that Gabriele had implemented (alog 17888). In order to resolve this issue, we edited the IMC_LOCK guardian so that it disables and enables the offsets when state is DOWN and LOCKED respectively.

Summary: Been going on since late February (~2-24) at ~24 hour period (last week at least.)  It is not obvious in the In-Loop or Out-of-Loop HEPI position sensors second trends.

See attached for 70 day trends showing the glitch being revealed after getting the sensor quiet (got lucky) and continuing to today.  Second plot zooms into glitch early this week 4-12 ~0400utc.  This one is a double glitch; they are not always the same but the first three this week are the sign and about the same magnitude.

Still looking for cause and other potential affects.

It is not incessent but the EndX HEPI Pressure still alarms occasionally at +-3.5 degrees F.  So I've opened the no-alarm region to +-4 degrees F.  See the attached plot for 1 weeks worth of minute trends.  You can see that this change should reduce the number of alarms from several a week to one or less.

Notice how much noisier the EX pressure is than EY or the Corner and the imprinted increase in the controller output.  It would be good to quiet down this signal.  EE is working on getting another (possibly custom) power supply.  Also, what is up with that ~24 hour glitch that hits the EY--warrants investigation.

Nice to see the daily changes on the controller output, presumably based on the temperature.  The last column of pressures are out of loop in the mechanical room, I thought those might have shown the cyclic signal too but they don't.  Does that mean the temperature isn't that important or is the temp in the MR as well controlled as the VEA...?

Attached is the plot for the front end laser output power for the past year.
The change around June 6th 2014 coincides with when the diode box was switched.

Not sure what the change around mid-August 2014 was caused by.  We should check
the power monitoring photodiode alignment and compare its output to a power
meter.

Sheila, Evan, Koji

• Tonight evan spent some more time on damping the 1stharmonic violin modes, more details coming later.  
• Several times today we increased the recycling gain by moving the ITMs in pitch (most moving ITMX down in PITCH), and each time we lost the lock.  Twice we were adjusting the alingment slowly, things seemed stable and we had sudden lock losses, April 16 22:05:49 UTC and April 17 8:42:35.  In both of these cases the ASC MICH P loop starts to have problems before the lockloss, although there isn't an oscialltion that grows, and there doesn't seem to be a satration in the suspension until after the problem has already started.  A next step to understanding why we are unstable with a recycling gain above 30 might be to make a good emasurement of the MICH ASC loops.  
• We have spent some more time looking at the noise that is contaminating the spectrum from 100- 50 Hz, which has been coming and going today.  We think that part of the story is as Gabriele suggested, (17912) SRCL noise which has a non stationary coupling that could be realted to dETM motion, or at least is predicted well by the AS45I YAW signal.  Evan and Gabriele added a more agreesive boost to DHARD YAW, which is not turned on by the guardian, which supresses motion in DHARD yaw, but does not make the SRCL coupling at 90 Hz stationary.  We also tried adding a bandstop to the SRCL loop around 100 Hz, this does not change the level of noise, so it seems that this mechanism can't expalin all of the non stationary noise we are seeing.  We also tried adding an offset to the DHARD YAW error point, by doing this we were able to make the noise a bit worse.  We would like to double check the phasing of the ASA 45 WFS.
• We measured the coupling from PRCL noise to DARM using a white noise excitation.  At 50 Hz this is approximately at the level of 3e-20, it should not be the limiting noise in DARM anywhere but now we can add it to the noise budget.  

Sheila, Koji, Robert, Evan, Alexa, Dan

We have made several measurements of backscattering from the OMC.  It seems like the reflectivity of the OMC is smaller by a factor of about 20 than what was seen at LLO, and it seems that backscatter from the OMC is probably not limiting our DARM spectrum.  

Two nights ago, we measured fringe wrapping by exciting the OMC suspension in the longitudnal direction, as well as by exciting OM1.  (related alogs 17910 17904 17882)  The attached plots show the DCPD RIM, with the DARM loop supression removed, with the excitations on.  

• First, we noticed that the osem calibration must be wrong, for both OM1 and the OMC.  For the OMC our knee frequency around 45 Hz indicates that indicates that our excitation amplitude was about 35.25 um.  The osem readback  indicates that our exitation amplitude was 11.8um, if we assume that this path length is double passed the osem is underestimating the motion by about 50%.  The story for OM1 is similar, the osem indicates that OM1 was moving with an amplitude of 6.25 um, but the path length modulation must have been about 20 um based on the knee frequency.  (Tobin's thesis, p 45)
• When we excite the OMC, we see two scattring shelves, the second has a finge velocity twice that of the first path.  For the first shelf we get an amplitude reflectivity of 1e-5, for the second shelf it is 1e-6.  These are eyeball fits, but they seem to be good to within about 15%.  At LLO (alog 13607) similar measurements showed an r = 2e-4 for their first shelf.  
• One speculation is that the first shelf could come from scattering within the OMC itself, and the second from the OMC refl path. Yesterday (after these measurements were made) Koji realinged the OMC refl QODs, and the amplitude of the second shelf is reduced today.
• FOR OM1 we only see one shelf, because OM1 is not the scattering source.  With this we are only modulating the path length between the IFO and the scattering source.  However, we measure the same reflectivity as the first shelf when exciting the OMC, so the two measurements are consisitent.

Tonight Jeff made a test of turning off the HAM6 sensor correction, as was done at LLO (third attachment) (LLO alogs 16814).  The spectrum is attached, but we do not see the dramatic fringe wrapping seen at LLO.  We would expect the impact to be smaller here than in LLO because our scattering amplitude is smaller and it is also likely that the microseism could have been smaller here.  

Today we Robert Koji and I made injections into all 6 DOFs on the OMC to see fringe wrapping.  We saw nothing by exciting roll or vertical, we were able to produce shelves by exciting L, T, P and Y.  The last screenshot attached shows the sectra with the various excitations on. For the record, here are times, all excitations were at 0.2 Hz, into the test filter banks.  While I've attached spectra of these, several off these shelves were moving around durring the measurement because of some lower frequency motion. 

LVEA: Laser Hazard
Observation Bit: Commissioning   

07:00 Karen & Cris – Cleaning in the LVEA
08:04 Bubba – Starting nitrogen purge of 3IFO storage containers
08:27 Filiberto – Working on TSC-Y rack
08:35 Gerardo – Turbo valve on HAM6
08:50 Gerardo – Out of LVEA
08:52 Peter – Going to the H2-PSL enclosure
09:15 Peter – Out of LVEA
09:23 Filiberto – Out of LVEA
09:35 Bubba – Out of LVEA
09:40 Adjust ISS diffracted power from 5.5% to 7.9%
10:25 Karen – Going to Mid-Y
10:25 Cris – Going to Mid-X
12:20 Dale – School tour of control room
15:35 Alarm on H0:FMC-CS_WS_RO_alarm – Have informed Bubba

Scott L. Ed P. Chris S.

This report will include the following dates, 4/14 thru today.
Tuesday the crew completed the X-1 beam tube cleaning. Test results posted here. All support equipment was relocated around the mid station to the X-2 beam tube. Began vacuuming support tubes and spraying bleach/water solution.

Continued vacuuming and began beam tube washing, cleaning 49 meters ending 4.6 meters past HNW-4-003 at end of day Wednesday.

Today the crew cleaned 61 meters stopping 1.5 meters beyond HNW-4-006.

The Apollo crew will be out on 4/17 and 4/20 so we will not be cleaning those days.

HAM6 system is running with only the 500 l/s "main" ion pump (valved out the turbo pump), the turbo pump still running.

We'll assess progress tomorrow and determine if we can turn the turbo pump off.

As noted by Evan et al, SRCL coupling to DARM is highly non stationary. I looked into three minutes of data with the SRCL noise injection described in the cited elog entry (GPS time 1113211711 + 180 s).

In brief, the coupling is modulated exactly as the residual motion of ASC-AS_A_RF45_I_YAW_OUT. If we compute the coherence between DARM and SRCL with a gain modulated by ASC-AS_A_RF45_I_YAW_OUT,  we get values very close to one. Read the rest of this report if you want to know more.

One strange thing is that it seems that the main contribution to this motion comes from ETMY PIT, even though the AS signal is YAW... See the last plot to see how AS_A_RF45_I_YAW moves in a very similar way to ETMY_L3_OPLEV_PIT...

Spectrogram, coherogram and tf-gram

The first attachment shows a spectrogram of DARM during the SRCL noise injection. The non stationarity behavior of the noise is very evident. The second attachment shows a coherogram, which is basically the same thing as the spectrogram, but showing how coherence changes over time. Again, coherence can go up to values of one, but clearly if you average over the entire time, you lose a lot since the coupling is non stationary. The third attachment shows the transfer-function-gram, which again shows how the transfer function from SRCL to DARM changes over time. You can see from the phase plot that the sign of the coupling flips multiple times. The 4th attachment is an animation of the transfer function between SRCL and DARM over time, which makes even more clear how the coupling changes amplitude and sign.

Band limited RMS

During the noise injection, I repeated the my standard BLRMS correlation with angular signals. I use the frequency band between 50 and 100 Hz. The correlation with angular signals (using all ASC error signals) is quite good, as shownm in the 5th attachment. I didn't continue further the analysis of which channels are more relevant, since the analysis described in the next section gives a better understanding.

Coupling variation over time

Looking at the transfer function over time (see for example the animation in the 4th attachment) it is clear that the shape remains mostly the same, and only gain and sign changes over time. I therefore computed the average of the TF around 93 Hz, which corresponds to a point where the phase is close to zero (this is just for convenience, in this way the real value of the TF is a good estimate of the gain variation over time). The TF gain varies a lot over time, and as expected changes sign many times. In the 6th attachment I show in the blue trace how this gain varies over time. The red trace is the best fit obtained using my algorithm and all ASC error signals. The green is the residual, which shows hoiw the reconstruction is very good. Using my channel ranking algoritmh I found out that the main contributor is  H1:ASC-AS_A_RF45_I_YAW_OUT_DQ is anticipatedm above. The 7th plot shows indeed that the fit is very good even if I use only this signal: so the conclusion is that the SRCL coupling is modulated completely by angular fluctuations visible in the AS port.

Coherence maximization

The 8th plot shows in blue the coherence between DARM and SRCL, if averaged over the entire 3 minutes of data. Clearly the coherence is kind of low, as explained above. The green trace is instead the coherence between DARM and an 'improved' SRCL signal, built as SRCL * (1 + gain * AS_A_RF45_I_YAW_OUT_DQ), with the gain obtained from the previous fit. The improvement is clear, showing that indeed I was able to recover most of the coupling gain and sign changes.

To get an even better estimation, I did an optimization based directly on the coherence. Basically, I considered the averaged coherence in the band 50-300 Hz, between DARM and a signal given by SRCL(1 + gain * AS_A_RF45_I_YAW_OUT_DQ). The optimal gain is similar to the one obtained with the previous analysis. However, the improved coherence is very close to one, as shown in the 9th plot. This is very efficient way to prove that indeed most of the SRCL coupling is modulated by the above angular signal.

Following up on the TTFSS work in alog 17885, we remeasured the input mode cleaner open loop transfer function.

The ugf is 50 kHz. With 3 dB of additional gain we can push this to 100 kHz and engage the second boost stage. The gain margin will be a little marginal at 1-2 dB, so.

For the measurement the common gain was at 18 dB, the fast gain at –6 dB, the compensation and one boost stage was engaged.

The small feature at 750 kHz is still there but of little relevance. This now closely resembles the iLIGO configuration and behavior.

Sheila, Gabriele, Evan, Koji, Dan, Alexa, Elli

Yesterday Koji, Evan and Sheila locked at 15W, and after an hour and a half the lock became unstable and they reduced they power due to suspected PI. A spectrogram ('darmspectrogram3_1.png ') of last night's lock shows a 844Hz line grow in the DARM spectrum (see attached spectrogram from 2015-04-15 09:30:00 UTC).  This corresponds to a PI at frequency 15540Hz, which is the first PI LLO saw (LLO alog 15934).  The line appears about an hour after the 15W lock began and the power was reduced after 1hr25min.  Once the power was reduced to 10W the line got smaller.  

This evening we locked at 15W at 2015-04-15 23:40:00 UTC and we saw the same line grow at 843.4Hz, corresponding to a PI at 15540.6Hz (see spectrogram 'spectrogram16April_843HzPI.png ').  This line grew untill we lost the lock at 1hr55 mins later ~ 2015-04-14 01:35:00 UTC (not due to the PI).  We measured the DARM spectrum around 15.5kHz using the SR785.  Attached is a plot '16AprilDARMSpectrum.jpg ' of the growing 15.54kHz line.

Grabriele saw that the 843Hz line was coherent between between the X-arm ASC QPDs and Darm, so we turned on the ETMx ring heater (see alog 17899).  The ring heater is requesting 1W total, or 0.5W each on the upper and lower segments.  We locked for a second time tonight at 15W at 2015-04-16 05:18:10 UTC. With the ETMX ring heater running, we didn't see any growth in the 15.54kHz line, as measured by the SR785.  See 2nd plot '16AprilDARMSpectrum_withETMXRH.jpg '.

Measurement notes:

-Spectrogram generated at LigoDV https://ldvw.ligo.caltech.edu/ldvw using channel H1:CAL-DELTAL_EXTERNAL_DQ.

-Spectrum meaurement taken with SR785 connected to OMC DCPD readout.  There is a script in /ligo/home/eleanor.king/netgib/SR785/SPSR785omcdcpds.yml that is used to take the spectrum (use the command <    ./SRmeasure SPSR785omcdcpds.yml > to take a measurement).

-Dan points out there are also OMC DCPD 64kHz  testpoints which are channels H1:IOP-LSC0_MADC0_TP_CH12 and H1:IOP-LSC0_MADC0_TP_CH13, which correspond to DCPD_A_INMON and DCPD_B_INMON.

Sheila, Gabriele, Elli

ETMx ring heater turned on at 15:04:16 1:56:00 UTC requesting 0.5 W in upper and lower segments.

The ring heater is on because it looks like we have been watching a parametric instability build up at 15540.5 Hz over the last hour or so of lock.  There is coherence between the X-arm ASC QPDs and Darm at this frequency, which is why we are trying using the ETMX ring heater.  There is a script  in /ligo/home/eleanor.king/netgib/SR785/SPSR785omcdcpds.yml that we have been using to track the amplitude of this mode (use the command <    ./SRmeasure SPSR785omcdcpds.yml > to take a measurement).

For some reason all of the gains on the ETMx upper and lower segments were set to 1, so I have changed them back to what they were in February (which is also what the ITMs are currently set to).

H1:TCS-ETMX_RH_SET UPPER&LOWER DRIVECURRENT_GAIN =12.5

H1:TCS-ETMX_RH_UPPER&LOWER VOLTAGE_GAIN =3.5

H1:TCS-ETMX_RH_UPPER&LOWER PCB_GAIN=3.5

H1:TCS-ETMX_RH_UPPER&LOWER CURRENT_GAIN=-0.08

Continuing on from yesterday's TTFSS work.

All notches were removed, and the transfer function was measured (see NONOTCHS.tif).
The peak at ~760 kHz is of no big concern.  However the peaks at around 1.77 MHz are.
These were notched out with C50 (1-65 pF) and series with L2 (220uH).  C50 was adjusted
to suppress the two peaks.  The transfer function was re-measured (see OLTF.tif).  The
unity gain frequency is around 450 kHz.

Currently the common gain is set to 27 dB and the fast gain to 5 dB.  Should the
loop break out into oscillation, reduce the fast gain to 0 dB, wait until the oscillation
stops and then increase it back to 5 dB.





Rick, Peter