Shiela showed me that PR3 alignment in Pitch is different for in vs out of lock, and it's about 1.5urad.

I've been looking at other optics, and today found that PR2 Pitch also has two distinct alignments of in vs out of lock.

Attached is a trend of PR2 during ER7, pitch on the bottom plot, that shows the two states.

The trend of PR3 pitch is essentially PR2 pitch inverted, however due to techincal dificulties, the plot is forthcoming.

Kyle, Gerardo

Finished replacing vibration cushions on Y-end and X-end Turbos -> Removed iLIGO RGA from BSC9 and replaced with 10" blank -> Finished torqueing flanges added yesterday -> Installed zero-length reducer and valve for aLIGO RGA -> Began pumping BSC10 and BSC9 annulus volumes 


Bubba 

Nearly completed 1" TMDS run at Y-end (still need one support) 


Danny S., Gary T. 

Hung door on BSC9 


END STATION STATUS -> Friday we will remove the 1st generation ESD pressure gauges from BSC9 and 10 and install 4.5" blanks in their place.  Next, we will install isolation valves and new style wide-range Inficon gauges on the domes of BSC 5 and 6 while leaving iLIGO gauges pairs as they are.  Then we will begin pumping the Y-end and X-end.  We will capture the pump down data using the existing gauge pairs while Richard M. arranges for the cabling of the new gauges into CDS. 

During ER7 there was some anecdotal evidence that the DARM gain was changing by a few percent between the handoff to DC readout and our high-power, low-noise state.  One place this could happen is in the power-up step, where we changed the DARM offset to maintain a roughly constant light level on the OMC DCPDs.  As the DARM offset changes the gain in the DCPD_Sum --> DARM path is scaled following a quadratic curve, but we know our approximation for the response doesn't include small static offsets, and maybe this has an effect on our gain scaling.  In this post I try to quantify this error - turns out it should be on the order of a few percent.

DARM Gain Scaling in OMC-READOUT Path

Stefan and I didn't explain this very well after we commissioned the OMC-READOUT path, so I wanted to document how the variables in this path are set by the OMC Guardian.  The carrier power at the AS port is assumed to follow a quadratic dependence on the DARM offset (see T0900023 for more math):

P_AS = (P0 / Pref) * (x / xf)**2          [Eq 1]

...where P0 is the input power, Pref is a power normalization factor, x is the current DARM offset*, and xf is an arbitrary constant we call the "fringe offset".

Step 1. When the OMC is locked on the carrier, Pref is set such that when the DARM offset is equal to the "fringe offset", x = xf, the output of the power normalization step in the OMC-READOUT calculation will be equal to P0:

Pref = (P0 / P_AS) * (x / xf)**2          [Eq 2]

Step 2. Small variations in DARM (dx) will generate small variations in the carrier power (dP) on the DCPDs, like so:

dP = (P0/ Pref) * (2*x / xf**2) * dx      [Eq 3]

The OMC-READOUT path calculates dx and sends the following to the LSC input matrix:

G * dx(x,dP) --> DARM_IN1                 [Eq 4]

..where dx is an explicit function of dP and the DARM offset, x.  The overall gain factor G converts dx into counts at the DARM error point.  G is calculated by taking the transfer function between dx and DARM_IN1.  It's set before the handoff to DC readout, and not changed.  After this point, the reponse of the light on the DCPDs to small length fluctuations (the slope, dP/dx) is assumed to be a linear function of the DARM offset, following Eq 3.

Static DARM Offset

When Stefan and I set up the OMC-READOUT path, Keita pointed out that a static DARM offset was making our lives more complicated.  Before ER7 I swept the DARM offset and measured the photocurrent on the DCPDs - the quadratic dependence has a clear offset from zero, see Figure 1.  The residuals for the simple quadratic fit (blue) have a linear dependence on the offset, while the residuals for the fit that includes a static offset (red) are well-centered around zero.  The best-fit value for x0 is -0.25 picometers, +/- 0.01 pm.  We're not sure where this comes from, whether it's changing, etc (on May 15 Stefan calculated 0.6pm).

Effect of DARM Offset on DARM Gain

If there's a static offset, x0, our model of the carrier power as a simple quadratic is incorrect, and Eq 1 needs to be rewritten as:

P_AS = (P0 / Pref) * (x + x0)**2 / xf**2          [Eq 5]

During the power-up step, we change the DARM offset to maintain ~20mA of photocurrent in DCPD_SUM, and we adjust the slope of dx(x,dP) accordingly, see Figure 2.  If we're using Eq 1 instead of Eq 5, this gain-scaling is incorrect, and our DARM gain will change.  For a negative static offset like we observe, the gain will be lower than it should be.

But, since the offset is very small, this effect is only 1-2%.  Without going into exhaustive detail, the ratio of the slopes for a simple quadratic, Ax^2, and a quadratic that is offset from zero, A(x+x0)^2, is close enough to 1 for small values of x0 that I don't think we need to worry about it, see Figure 3.  The error in the gain as we move from a DARM offset of ~42pm at 2.3W input power to ~16pm at 24W is 1% for x0=-0.25pm.  For x0=-0.75pm the effect is 3%.

Summary: We have a small static DARM offset, this means our approximation of the DARM gain as a function of DARM offset is a little wrong.  The effect should be small.  Eventually we will account for the DARM optical gain in the calibration (the 'gamma' parameter) and small changes in the DARM loop gain will be absorbed into the calculation of CAL-DELTAL_EXTERNAL.

Edit: On further reflection, this isn't the case.  We have a small static offset while locked on RF DARM, but after the handoff to DC readout this offset is absorbed into the power normalization (the Pref variable, Eq 2).  Once DARM is locked on DC, a zero offset will result in zero carrier light at the dark port, by definition.  A small offset might change the gain scaling at the handoff such that we observe a few percent difference from what we expect, but the mechanism is not what I describe here.  Will have to think about it more.

* In the OMC-READOUT path, the DARM offset is referred to as OMC-READOUT_X0_OFFSET.  Here I call it 'x', and refer to the static offset as 'x0'.  Sorry.

A while a go RichM gave me some new blend filters to try. Because we have no IFO, I've installed them on ITMY in the X and RY dof's. I'll leave the ISI like this overnight to get a good long quiet stretch to compare data with.So far, not much to say. I'll put more detail in tomorrow.

I used the sitemap to look at the code revision numbers of each timing device. All DuoTones, Master/Fanouts, and Comparators are programmed to the correct code revision (documented at https://awiki.ligo-wa.caltech.edu/aLIGO/TimingFpgaCode). The 3 issues are:

1) The C_MA_A IRIG-B in the MSR shows Rev. 0. This is a known issue and will be corrected by reprogramming the IRIG-B when possible. The IRIG-B seems to be producing the correct time code output, so we're going to test the effect of a temporary (< 15 minute) interruption to the IRIG-B signal on an IRIG-B device in the test stand to see whether we can reprogram the MSR IRIG-B without causing hiccups.

2) The other 2 IRIG-B in Y_FO_A and X_FO_A show Rev. 133. They should show Rev. 113. They are otherwise operating nominally. It is possible that the timing wiki needs to be updated, or that the revision number was entered incorrectly in the firmware source code.

3) All of the Oscillator Locking slaves in Y_FO_A, X_FO_A, and C_FO_A show Rev. 83, which is the deprecated code. They are operating nominally. Again, this could be an incorrect revision number.

We need to check whether 2) and 3) are meaningful problems that need correction.

Note, as a further contamination test, we blew the N2 gun across a new 4" witness wafer for the same amount of time/distance as we did during the discharge and inspected.  We blew for 30sec at 20psi 2" from the wafer.  Upon inspection, we found the wafer still looked very clean, as expected.

We have been stating the witness wafers as 3" wafers, but in-fact they are 4" wafers.  There are not 2 sizes on site.

Today we finished up the ETMx in-chamber activities adn closed the door.  Sequence of events:

Filiberto checked for TMS QPD cable grounds at the feedthru.  All ok there. (Actually did this yesterday afternoon.)

Kyle and Gerardo finished the port work (that was scheduled in the original vent plan).

Fil check the ESD pinout with aid from an "inside" guy multiple times in order to make clear the understanding of the pins on the air-side of the feedthru.

Jim unlocked the ISI.

Performed the discharge procedure on ETMx as per T1500101 - again, this took around 1 hour.

Swapped the vertical witness plates (1" and 4") that were mounted on the QUAD structure.  1"  optic vertical on floor is now: SN 242.

Removed all equipment and re-suspended lower masses.

Dust counts taken throughout.  Counts were nomnally 30-200 counts in all sizes of particles with few bursts up to 500 in th 0.3um size once in a while when 2 or more people were moving in chambelr.  Counts were zero or 30 (max when entering chamber after lunch or in morning.

Measured ETMx main and reaction chain P and V TFs.  All looked healthy with purge air on and soft cover over door.

Door being put on.

Checked EQ (earthquake) stops (Note this is the same as we found/set on ETMy):

Barrels of ERM ~2mm

Barrels of ETM ~1.5-2mm

12 o'clock stop ~3+mm

PenRe barrel ~1.5-2mm

PUM barrel ~2mm

All face stops 1-1.5mm

ETMX ESD

1. Continuity test was done on each pin to verify each section LR, UR, BIAS, UL, and LL. 
2. The old vacuum feedthrough was removed by Gerardo
2. The in-vacuum cable was re-terminated for installation of the new UHV 5-way coaxial connector.
4. In-vacuum cable was connected to feedthrough
5. Gerardo installed new feedthrough.
6. In-air cable connected to feedthru.
7. All pins were HIPOT tested to 800V and passed.
8. Pins were rechecked, by grounding each section to ground (in chamber) and verifying at feedthrough (air side).

 Pin layout for ESD (@ Feedthrough) is as follows:

   Pin 1 - LR
   Pin 2 - UR
   Pin 3 - BIAS
   Pin 4 - UL
   Pin 5 - LL

Following E1400430, Pin 1 is slightly offset in spacing from the other pins.

Removed 4" wafer from HAM6, (T1500311).

Took PET swipe from south side of chamber from base of OMC to edge of the ISI table.

Both samples have been prepared for processing at CIT.

Note: The placement of the 4" wafer was in a difficult spot to remove. One had to lean into the chamber on an off balance stance and remove the wafer from the center of a group of small optics. There were no good handholds or bracing points available. The wafer being placed flat on the ISI table had to be pushed across the table until it came up against a cable clamp before one could get the tweezers under it. There was a risk of bumping or disturbing the optics around the disk. See attached photo. 

Dust counts taken during work, inside and outside the chamber were all zero or in the low 10s of counts.

Summary: A seismometer was buried 40 m from EY to take advantage of strong attenuation of the tilt signal relative to the acceleration signal from distant sources. Seismometers located outside the buildings may be useful in reducing problems associated with tilt.

Our buildings are tilted by wind. Our seismometers do not discriminate between this tilt and acceleration (like a pendulum), so wind-induced tilt produces spurious control signals that can make it difficult to lock and maintain lock. A tilt sensor can be used to discriminate between tilt and acceleration, but we may also be able to discriminate between the two by taking advantage of source differences in the band below 0.5 Hz, where tilt generates the largest spurious acceleration signals. The tilt in this band is mainly generated locally by the wind pressure against the walls, while the acceleration signal is mainly generated by ocean waves and other distant sources.

While the seismometers are in the far field for most low frequency accelerations, they are in the near field for building-generated tilt (wavelengths at 0.1 Hz are about 50 km). To take advantage of the rapid attenuation with distance in the near-field, I buried an STS-2 seismometer in a meter deep hole I dug 40 m from EY (Figure 1).  Figures 2 and 3 show a comparison of the buried seismometer to the SEI seismometer on the ground inside the EY station. During the low wind period the spectra look virtually identical below 0.5 Hz and the coherence is high because the sources are mostly distant and the wavelengths are large. During the high wind period, the buried seismometer doesn’t change that much (there is some change in the microseismic peak because high/low wind were about 24 hours apart), but the building seismometer shows a huge signal from tilt.  The coherence in windy conditions is low because the tilt is highly attenuated 40 m from the building. Figure 4 shows spectra for higher wind, 15-35 MPH.

Of course the external seismometer would not detect real building accelerations due to the wind. But if the unwanted tilt signal dominates over the wanted wind acceleration signal, a seismometer outside the building may be useful, and I think that this is the case below about 0.5 Hz.

I note that I first tried this in the beam tube enclosure tens of meters from EY, but found that the wind tilts the beam tube enclosure almost as much as the building (but not coherently), supporting a hypothesis that aspect ratio is the important variable. Also, Jeff points out that, if we insulate the buried seismometer well (and I did not) we might even be able to do better than the building seismometers with their current insulation during even low-wind periods. Figure 5 is like Figure 2 except that the signal from the stage 1 Trilliums is included.

Kyle -> Soft-closed GV7 and GV5 -> Vented HAM6 

Bubba, Hugh, Jim W. -> Removed HAM6 South and East doors 

Kyle, Gerardo -> Installed NEG and TMDS reducer nipple+valve+elbow at X-end 

Danny S., Gary T., Gerardo, Kyle -> Hung North door on BSC10 

(NOTE: Noticed ~1 hour before hanging door on BSC10 that the purge-air drying tower had been left off since tying-in the 1" TMDS line on Monday afternoon -> Turned it back on and notified the ETMY discharge crew

Dan Hoak gave us a clue on page 19067 and then Bas Swinkels ran Excavator and found that the channel H1:SUS-OMC_M1_DAMP_L_IN1_DQ had the highest correlation with the fringes. Andy Lundgren pointed me to equation 3 from “Noise from scattered light in Virgo's second science run data” which predicts the fringe frequency from a moving scatterer as f_fringe = 2*v_sc/lambda. Using the time from Dan and the channel from excavator and the fringe prediction, I wrote the attached m-file. Fig 1 shows the motion, velocity, and predicted frequency from OMC M1 longitudinal. Figure 2 shows the predicted frequency overlayed with the fringes in DELTAL. Math works.

PS. Thanks to Jeff and the SUS team for calibrating these channels and letting me know they are in um. Thanks to Gabriele for pointing out an error in an earlier draft of the derivative calculation.

We had four known reasons for having difficulty locking today, one is an unsolved mystery that might be hurting us more often than we realize.

• The BS limiter was off durring DRMI lock acquisition, this is turned on and off by guardian.  I've attached a screenshot of the gaurdian log.  The code should have returned true imediately after having turned off the limiter, and proceeded onto the next state, however, it ran the LOCK_DRMI_1F run again.  The requested state at this time was DRMI_1F_OFFLOADED, which means that this guardian should have moved onto the next state.  Is there a way to search the Guardian logs to see if we have had other instances of this?
  • we have seen this behavoir in the past, and Jamie suggested that this could have been because the state LOCK_DRMI_1F was requested.  I know that was not the issue today, but I changed the state so that it is no longer a requestable state anyway, since it should never be requested.
• The roll mode damping for ETMY was switched off at the output.  All the roll mode damping settings are now enforced by the guardian, using ezca.get_LIGOFilter().only_on.  

I reloaded both ISC_DRMI and ISC_LOCK guardians today, to incorporate these changes.  

• We had difficulty transitioning to ETMY ESD, evan is writting an alog about what we think is the solution
• Now the winds are quite high, the forecast says they will die down around 1 am.  

Good luck TJ!