VM server hosting alog, awiki, SVN, and CDS-Bugzilla hung overnight. I captured the crash dump screen and logs this morning then restarted host and guests. Services restored around 9AM PT.

no restarts reported

J. Kissel, S. Dwyer, A. Staley, N Smith

Continuing Shiela's investigations from last night (see LHO aLOG 14883), we put our heads together to figure out why we're having so much trouble with the ALS DIFF control. I attach plots comparing what is currently installed against when I last was involved with the ALS DIFF design (see G1400146, and the subsequent design that was used never got published, but was designed using ${SusSVN}/trunk/QUAD/Common/FilterDesign/HierarchicalControl/DARMmodel_ALS_20140428.m). Note this is also around the time that we increased the UIM driver strength by a factor of 4, and this WAS included in my 2014-04-28 design.

Some Comments and History that I think has caused in the current badness:
- After initial installation by Kiwamu (see LHO aLOG 11665), Stefan, Sheila and Kiwamu had lowered the UIM / TST crossover a bit, from 2-ish [Hz] to 1.5-ish [Hz] (see LHO aLOG 11899). From that entry, "These tweaks served to (1) to move the elliptic filter's gain peaking bump out of the way of the 10 [Hz] features in the input noise, and (2) roll off the low-frequency end of the test mass drive faster." These adjusted filters are shown on pg 3 and 4 of the attached, shown in solid lines. The dashed lines are the original filters. One can see there's a good amount of phase action and amplitude ripple around 10 [Hz]. The cross-over action happens over a wide frequency range from 0.6 to 20 [Hz].
- At the time, we were mystified why we were never able to get to the 15 [Hz] UGF I'd designed, but we moved on before figuring it out. With some finagling, one could only get the UGFs to 5 to 10 [Hz].
- Over the course of a few weeks, Stefan, Sheila, Arnaud, and Keita began to add tweaks and patches to the plant-inversion portion of the distributed hierarchical design. This is the source of the "invL2LNEW," "patch," "LISOfit" "invL2L1," "invL2L2," "MatchedinvL2L" filters that are now used. It's unclear if this completely solved the stability problems, but it tweaked the phase in the right regions enough to certainly help. Sometimes.
- This was followed by Arnaud pioneering the length-to-pitch decoupling filters, but those installs never really went well (see, e.g. LHO aLOGs 11952, 11849, 11832).
So -- as we left ALS DIFF before the summer vent, we could only ever get the UGF up to 5 to 10 [Hz], had trouble with its stability and cross-coupling to pitch, had installed a whole bunch of high-Q plant compensation filters. Indeed, these very-precise compensation filters were measured specifically for ETMX, and then copied and pasted over to ETMY (dubious).

- Quite a bit after this, after the summer vent, we (discovered / became confident) that the actuation strength or the ESDs were lower than I modeled by a factor of 2-to-4 (see, .e.g. LHO aLOG 12220) due to charge plaguing the electrostatic drive system. 
- Further, not only is it weaker by a factor of 2-4, but the strength of the ESD *varies* on the hour timescale because of continuous charge noise from ion pumps, requiring the cross-over between the UIM and TST to constantly need adjustment (needed both at LLO and LHO, but never really reported), and (I believe) occasionally moving the cross-over into instability.
- Further, further, because the charge on the quadrants evolve differently, which mean the length-to-pitch coupling is constantly evolving for this stage. We currently do not have *any* compensation for it (frequency dependent or independent).
- Distracted elsewhere, I never got back to modeling whether one could get a stable, 10 [Hz] UGF ALS DIFF loop, that did not saturate the SUS DACs. Not to mention, ground motion / SEI performance has evolved. As such, we haven't changed the cross-over of the distribution filters for the weaker, time-dependent, ESD drive.
- After finding that the highest vertical and roll modes were getting rung up with lock-acquisition, and saturating actuators, high-Q notches were added at 9 and 13 [Hz]. First to the DARM filter bank, and then moved to the UIM stage (LHO aLOG 14672). These are the "BandstopBR" that are now used in the UIM plant inversion filters. These cause substantial phase distortion near (a) the constantly evolving UIM / TST cross-over, and (b) the unity gain frequency of the loop depending on where they lived. NOTE: Sheila did NOT include these notches in her open loop gain plot (pg 1).

So things we know now that should aide new design considerations:
- The ESD actuators are weaker by a factor of 2-4, and they vary in time. 
- So we need lots of gain margin both at the cross-over and the overall loop UGF.
- We should try to decrease the wide-frequency range impact of the UIM / TST distribution filters.
- We need 9 and 13 [Hz] notches in the length control path, because lock acquisition impulses cause them to ring up.
- Length-to-angle, though probably does not play a roll in the ALS DIFF loop stability at 10 [Hz], it does play a roll in the slow alignment fluctuations. In this case "slow" is both at 0.15 [Hz] as well as on the "DC drift," minute time-scale. It's unclear which stage is causing the problem.

  In order to see the effects of glitches in the BS oplev damping I requested that the servo be turned off for an hour yesterday.  
The attached figures show the effects of turning off the servo.
  
1) The spectrogram shows the relative change in the pitch, yaw and sum spectra when the servo is turned off at about 1900s and turned on again at about 5000s.
     1a) Note the low frequency kicks which both the pitch and yaw servos are introducing due to glitches in the laser power.  Stabilising the laser power may benefit this oplev.
 
2) The ASD plots show the change in the spectrum when the damping is turned off. 
     2a) The Yaw damping is good over a broad range of frequencies.
     2b) The pitch damping loop requires to be tuned further to reduce the servo bump between 2 - 6 Hz
     2c) The pitch loop also has slightly excess noise at low frequencies.

 [Hugh R.  Suresh D.]


     Yesterday we swapped out the HAM3 oplev laser (Sl. 122-1 was replaced by Sl. No. 199).  However the Sl# 199 which had behaved well in the lab for four days chose to go into wild 100% power drops when placed in LVEA.  The period between drop outs increased gradually as the laser approached thermal equilibrium (see the attached pic). However this was not a stable configuration so I brought it back to the lab and found that the problem was with the laser temperature servo.  The power drop outs went away after a bit of tweaking of the servo gains and the set point (which was too high).  

      The Sl#199 has been replaced back in the HAM3 oplev and I am monitoring its performance.  

Alastair, Greg, Eric

The X and Y tables are now almost complete.  We have installed and aligned the FLIR camera, screen and cover (thanks to Greg's machining skills) on the Y-table - it currently has a beam dump in place to protect it.  Main beam path on Y table also has a beam dump in place.

The power on the thermopile head at the output of the laser has been calibrated for both X and Y lasers.  The rotation stages have been calibrated such that requested power should be correct (we note that sometimes you need to repeatedly hit 'minimum power' to get the rotation stage to go to the correct angle) on both tables.  The on-table power meters have been calibrated for the power incident on the CP on both tables.

The X and Y tables both have flipper mounts installed and working on table, along with sensors for the mounts.  The script to flip the mirrors that is connected to the MEDM screen is not yet working properly (possibly an issue with the sensors which it uses to test mask position).  On the X table the flipper mounts are currently connected but out of the beam path, and the mask is being held in a fixed mount.  On the Y-table the flipper mounts are both in place, however only the central mask is in its flipper mount.  For this reason I've disconnected the flipper from its power supply to stop it accidentally being moved out of the beam.  I've taken images with the FLIR camera on the Y-table that suggest that we could get better alignment through the mask.

Much progress on 3rd IFO storage - we've basically been through everything on site for the CO2 laser.  At the moment we're still looking for the AOMs that we know are here (Thomas gave us serial numbers for these).  Other than that, there are some other parts listed in ICS as being at CIT and we'll look for them there.

Though we are not directly touching the BS (there's no actuator for it), based on some a theory that 2449.25Hz line (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=14855) might be the BS butterfly, I put a band stop ellip("BandStop",5,1,40,2440,2460) in FM2 of H1:SUS-BS_M3_ISCINF_L, and turned it on.

If we continue to have this line rung up, we know that it's not BS butterfly.

K. Venkateswara

Sensor correction on X and Z at ETMX was left on last night. I turned it off this morning at 8 am as Filiberto and I were planning to work in the EX VEA. I modified the temperature sensors to take in +/-12V from the PEM power supply (thanks to Filiberto) and added a differential amplifier (with gain~50) to it.

In the afternoon, wind speeds were routinely hitting 50 mph. I've attached a pdf showing the ASD of the ground motion, BRS output and Stage 1 motion and some interesting coherences. Sensor correction was off in X and Z during this period.

Sensor correction has now been turned on and I will add plots of the result later.

08:13 Jeff B. and Andres moving 3IFO storage equipment in LVEA
08:26 Hugh restarting end Y HEPI database
08:29 Krishna retrieving tiltmeter thermometers from end X
08:49 Ed, Manny and Filiberto re-routing PEM cables at end X (WP 4935)
09:42 Alastair connecting sensors on TCS X and TCS Y tables
10:00 Cris checking for water leaks under rollup door at end Y and mid Y
10:21 Karen cleaning at end Y
10:27 Vending machine delivery truck through gate
10:32 Vending machine truck through gate
10:34 Cris back from end Y and mid Y
10:57 Kyle picking up tools and running scroll pump for ~ 30 seconds at end Y
11:16 Karen done at end Y
11:45 Gerardo taking inventory of cameras and illuminators at end Y
11:45 Kyle back from end Y
12:06 Gerardo done at end Y
12:53 Filiberto done at end X
13:07 Filiberto picking up tools at end X
13:08 Mitchell and Andres retrieving tooling from LVEA
13:13 Gerardo taking inventory of cameras and illuminators at end X
13:24 Mitchell and Andres back from LVEA
13:45 Jeff B. and Andres moving 3IFO storage equipment in LVEA
14:05 Gerardo done at end X
14:20 Dan taking picture of board at HAM6
14:20 Travis escorting visitor on tour through LVEA
14:50 Jeff B. and Andres done
15:49 Jeff K. taking tour through LVEA
16:13 Jeff K. out of LVEA

Continue cleaning up PEM cabling. This morning we powered off the PEM AA chassis and disconnected all floor bnc cabling for PEM Tilt, Seis, Mic, Magnetometer, and infrasound mic. The cables were pulled back and routed into cable tray over the beam tube. All excess cabling was cut off (up to 20 ft on some cables) and re-terminated.

Few cables left to terminate, ran out of time before noon deadline. Plan to run MIC and Op Lever power cables tomorrow.

This entry summarized the status of REFLAIR_B signals. REFLAIR_B is the broadband photodetector, D1002969, mounted in reflection of the interferometer which is responsible for measuring the 3f signals at 27 MHz and 136 MHz in DRMI. The 3f signals are relatively weak, especially at low modulation depth. This has lead to a low signal-to-noise ratio at sub milliampere photocurrent and distortion problems above a milliampere. The problem of saturation by out-of-band intermodulation products was recognized early on a LLO and fixed with a diplexer amplifier, D1300989.

The situation at LHO and LLO are essentially the same.

• LLO operates with 0.2 mA of photocurrent and can lock both the DRMI and the full interferometer. The signal-to-noise is not great and sensor noise dominates the 3f locking signals above 20 Hz. The modulation depth is three times the design value and will generate some excess light at the antisymmetric port.
• LHO operates around 4 mA of photocurrent and can lock DRMI with a better signal-to-noise ratio in the 3f locking signals. However, the signals have a strong dependency on the incident power, see here.

Koji has recently measured the second order intermodulation products of the RF chain in the broadband photodetector and found the second order intercept point to be rather low, around 30 dBm. This is maybe not too surprising considering these RF amplifiers are single transistors or Darlington configurations operated around a fixed DC working point. No specification of the IP2 is given in the datasheet.

This leads to the conclusion that 3f signals at LHO are predominantly due to intermodulation distortion in the RF amplifier chain and not due to the optical signals. This obviously works just fine for the DRMI, but probably doesn't give the required immunity to the carrier mode for full interferometer locking.

Possible solutions:

• Try to operate LHO at low photocurrent and re-optimize the DRMI locking signals.
• Removed the first amplifier stage from the broadband photodetector. This will remove 22 dB of gain and hopefully greatly reduce the RF distortion. The dark noise of the photodetector will increase by about 3 dB. At 27 MHz we should be shot noise limited with 0.2 mA of photocurrent. So, this should have little effect on the sensor noise. However, at 136 MHz the shot noise limited sensitivity is around 2 mA, so we should see a ~1 dB increase in the noise level.
• Get the 3f photodetector which is based on a tuned design into fabrication.

Increasing the modulation depth and reducing the photocurrent at the same time will not improve the situation, since the distortion depends on the absolute signal strengths of the individual RF lines. However, removing the first amplifier stage should give us enough room to further increase the modulation depth and improve the signal-to-noise ratio. Using a high modulation depth during locking may require an adjustable EOM driver, such as the, D0900760.

Betsy, Travis

This alog represents the last ~month of intermittent assembly work on the 3IFO QUAD unit "Q7".

After switching out 3 problematic wire segments and the entire set of top stage blade cartridges, we have finally launched a first round of testing on Q7 this morning.

Details:

After assembling and fully suspending Q7, we had a difficult time bringing the 6 DOFs of each chain into coarse alignment.  We discovered that the top most blades used in the QUAD were the softest of any QUAD unit thus far, as per the stiffness catalog T1000068.  In fact, this set had a much wider variation in stiffness than any other unit as well which was adding to our challenge.  We decided that we should delegate this set of blades to the spare bin and swap them with another set.  After swapping in a set from the middle of the stiffness range (Tops Set 7), we saw the QUAD chain alignment was much improved in side shift.  We then continued to struggle with differential height.  We decided that we might have had a wrong wire segment length lower in the chains so we first switched in new main chain PUM loop which had no effect, and then switched in a new set of reaction bottom and final wires which did help our differential height issue.  (We confirmed the removed sets were ~1-2mm longer than the new set although we really don't know which is "correct".)   With all of this new hardware, we were able to align the chains to within the coarse specs.  We laced up the reaction chain lower stages and readjusted alignments and suspension mechanical groundings.  Yesterday we assembled the top mass tablecloth and cabled/attached/aligned top 12 BOSEM sensors.  Today we are running TFs.

Over the past 2 days, there has been a series of earthquakes (26 so far, ranging from 2.5 to 4.7 magnitude) near Lakeview, OR, approximately 400 miles south of LHO.  Something for commissioners to keep in mind as they struggle to lock the IFO.  See attachment.

Nic, Alexa, Sheila, Evan, Dan

We wanted to measure the crossover between L1 and L3 of ETMY. We took a transfer function from LOCK_L1/L3 to ALS-Y_REFL_SERVO_CTRL_OUT with green locked to the yarm. We found an old template made by Sheila and Stefan for the L1 stage. We repeated the measurement for a few data points (green trace), and it seemed the same as the old measurement (blue) so we aborted the measurement and went with the assumption that it was still a valid measurement. We then measured for the L3 stage (red trace). Clearly the crossover between L1 and L3 is about 2 Hz as expected.  Nic plans on dividing these two transfer functions tomorrow morning... 

Fo reference the xml file is located here: /ligo/home/sheila.dwyer/ALS/HIFOXY/Y_UIM_2.xml

After spending far too long scratching my head about calibrating the OMC DCPD signals, I've measured the RIN of the OMC transmitted beam, and it's not pretty.

To make the measurement I locked the OMC on the side of a carrier TEM00 fringe, as described here.  I measured the open-loop transfer function; this is the first plot attached (UGF is 100Hz, which is about the same as when we're dither-locked on the peak of the fringe with much higher gain in the LSC servo).  To calibrate OMC-DCPD_NORM into true RIN I divided by 1/(1+G) in DTT so that the loop suppression is accounted for.  To calculate the RIN seen by other PDs, I divide by the PD sum at DC.

The results, in the second plot, show that the beam incident on HAM6 has some issues.  At high-ish frequencies, 100Hz and up, the OMC Trans intensity noise is due to noise out of the mode cleaner.  It's coherent with IM4 Trans and the ISS second loop PDs.  Probably this noise can be mitigated using the ISS second loop and also reducing the IMC angular fluctuations that were described by Gabriele.

At low frequencies, between about 0.2 and 3Hz, there is huge intensity noise on the input beam to HAM6 beam that is not seen just after the IMC (neither IMC_TRANS or the ISS second loop PDs).  The noise is seen in HAM6 by the OMC QPDs (in green - limited by electronics noise above 50Hz?) and by ASC-AS_C (dashed black).  At high frequencies the intensity noise in HAM6 is coherent with the noise out of the IMC, but the loud stuff around 1Hz is likely due to the clipping that Keita measured yesterday.

The third plot shows an attempt at characterizing the length noise of the OMC; the loop-corrected RIN was converted into meters using the derivative of the usual Fabry-Perot transmission formula at half-resonance (the conversion factor is 3.7e8 RIN/meter).  This is a first step towards building an OMC noise budget, following the work by Zach at LLO.  At high frequency (around a kHz), the noise begins to drop below the limit of 3x10^-16 meters/rt[Hz] prescribed by Valera's estimate in G1100903, but there's a forest of lines around 1kHz that's not unlike what was observed at L1.  At lower frequencies, the noise seen at the DCPDs is dominated by the input intensity fluctuations, and it's not possible to measure the length noise that's intrinsic to the cavity.  The photocurrent during these measurements was about 3mA for each DCPD (shot noise RIN of 10^-8/rt[Hz]).

Alexa, Evan

The ETMY oplev damping was off. We have turned both picth and yaw damping back on.

Additionally, I have tweaked the filters and the gain slightly in order to reduce gain peaking:

• Pitch now has an elliptic low-pass at 15 Hz rather than a Chebyshev at 10 Hz. The gain is now -0.3 ct/ct.
• For yaw, the filters are a 0:0.1 z:p pair, a broad notch at 0.6 Hz, a 15 Hz elliptic low-pass, and a notch at 1.33 Hz (this peak shows up in the yaw spectrum and I assume it is the PUM pitch mode of the suspension).

According to conlog, the loop gains appear to have been randomly adjusted several times over the last week.

We hope that this might improve the robustness of the ALS locking. If not, we might try a similar recommissioning of the ETMX oplev damping (since this are also off).

As the wandering laser intensity continues I intend to learn more about these systems. I can only report the findings and make the adjustments. ISS diffracted power is down to ~5% this morning. REFSIGNAL was at -2.04V as it was set by me yesterday. Today I have adjusted REFSIGNAL to -2.02V to bring the diff power to ~8.6%. Attached is a past 5 day trend. the spikes, i am told,  are likely caused by activations on MC2? (for example)

Evan, Sheila, Nic, Lisa

To answer Peter's questions , we have relocked the DRMI (without arms) on 1f and 3f 
(10W input power, 27 mW on the BBPD photo-detector).

The DRMI was very stable in both cases, here are the good times:

 Nov 5, 6:00 - 6:15 UTC  DRMI locked on 1f, WFS on 

 Nov 5, 6:30 - 6:45 UTC  DRMI locked on 3f, WFS on 

Evan is about to post plots with error signal spectra.

It is probably a good idea to make some plots with ground motion/ISI/optical lever signals to "capture" these good times.