Data for the past 3 days.

Arnaud posted about CPS glitches in the CPS HAM5.  Though it prudent to scan LHO for similar.

I looked over the past three weeks and found none that were shaped like LLO (very narrow spikes to near 40k counts.)  WHAM6 had some associated with the fast shutter although I did not establish cause/effect there.

WHAMs 2 3 4 & 5 all had one exceeding 20k counts at the same time 0030 utc 30 March but was not a single spike, looks more like an Earthquake.  Bottom line, we should be ever vigilent but for now, LHOs HAM CPSs are not glitching.

LVEA: Laser Hazard
Observation Bit: Commissioning   

07:00 Karen & Cris – Cleaning in the LVEA
10:05 John & 3IFO Group – in LVEA taking measurements at beam tube building exits
10:18 Gerardo – At HAM6 to turn off scroll pump
10:30 ISS FSS have been saturation and the IMC is dropping out of lock. Per Peter K. turned off the ISS Autolock to see if that stabilizes the FSS and IMC.  
10:43 John & Co – Out of LVEA
10:45 Gerardo – Out of LVEA
12:20 FSS is still saturating and the IMC is dropping out of lock. Per Peter K. dropped the FSS Common Gain from 25 dB to 24 dB. 
15:08 Gerardo – Going to H2-PSL enclosure

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.

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.

Two tip-tilts have been assembled for 40m.  They are sitting on the optics bench in the Optics lab.

These have thinner wire (43 microns in diameter) to avoid the hysterises seen in the thicker 125 micron wire.  Therefore these have to be handled more carefully.  The wires are quite unforgiving of any kinks or handling errors.

As agreed, these do not contain BOSEMs.  Type-B (one stage before the production line)  bosems will eventually be used in these.

The tip-tilts are ready for shipment to 40m.  They have been wrapped in Al-foil.  For long term storage, these have to be stored in a dry atmosphere to avoid rusting of the "piano wire" fibers.  The mirror holders are locked into place for shipment using the eddy current dampers on either side of the mirror mounts. 

The Sl nos are 007 and 038 (Bottom Plate).  Images of the assembled tip-tilts and their various reference numbers are attached.