Summary:

Green straight shot beam size on ITMX is a factor of 0.87 of nominal (i.e. too small) while ITMY a factor of 1.2 too large.

The beam radius ratio is (X/Y)=0.72, which makes the ITMX baffle PD output current to be a factor of 2 larger than that of Y when you hit these PDs using a straight shot beam.

There used to be a factor of 2 to 2.5 unexplained difference between the photocurrent in ITMX and ITMY baffle diodes during initial green alignment, but the beam size explains a factor of 2, so the remaining factor is about 1.2 or so, which I don't care for now.

Background:

This is one of those health check type stuff. Baffle PDs could be used for scattering measurement but the health of some of those PDs were in question.

One of the suspicions came from the fact that, when looking at green straight shot beam during full initial alignment, PD current from X arm baffle is much larger than Y arm. A part of it comes from the laser power (there's about a factor of 2 or so difference) but the baffle PD current is a factor of 4 to 5-ish different, so there always was a factor of 2 to 2.5 unexplained.

Details:

I first used dither align script to point the TMS beam to PD1 and then PD4 of the ITM baffle. Since the horizontal distance between PD1 and PD4 is 11.3", the script allows us to calibrate TMS alignment slider.

Immediately after the script finished, I pointed the beam to PD4 center, move TMS in YAW in one direction by more than the beam radius,  and ran another script to move TMS in YAW, wait and measure PD4 current.

Attached is the YAW scan data (circles and crosses) as well as the fit to Gaussian profile assuming the same radius in PIT and YAW:

current = ofst+ A * 2/pi/w^2 * exp(-2*(X-X0)^2/w^2)

where w is the beam radius and A is an overall factor.

The last column in the above table shows QPDA_SUM+QPDB_SUM. If everything makes sense, and if the beam was at the same height as the PD center during the scan, QPD_SUM ratio should agree with A ratio, but apparently it doesn't at 20%-ish level. This is good enough because the suspicion was that there was something grossly wrong about the baffle PDs.

BTW we can do the same thing for IR beam, scanning MMT3, to assess the IR matching to the arms if we want to (or better yet, do the spiral scan to see both PIT and YAW).

Looks like lock was from about 9:14 UTC to 16:09 UTC. For posterity.

http://earthquake.usgs.gov/earthquakes/eventpage/nc72387946

Ground velocity exceeds 20 μm/s from 0.03 Hz to 0.1 Hz. IMC MC2 transmission is noticeably wobbly.

Added 2 channels and removed 788.

Work Permit review.

SEI - continuing work on SDF system for BSC ISI. HEPI pump servo is ongoing tinvestigation. Maybe Jeff will run some TFs looking at 1Hz to 10Hz at some point today.

SUS - no big news. Thomas will ressurect the Drift Monitor this week sometime.

ISC/Commish - taking small steps in the positivedirection. Had a rather lengthy DRMI lock last night beginning ~01:30.

3IFO - no activities in LVEA. All activities across the street.

Facilities - Beam Tube cleaning is ongoing. Gutter work is don at LSB. Crew has moved to VPW.

CDS - variac installation at End station for Heater. Work in HAM6 area on Fast Shutter. R Abbott will be coming to work with this.

Gary will be moving ISS arrays and using the large airlock door in the LVEA

model restarts logged for Tue 27/Jan/2015
2015_01_27 01:43 h1fw0
2015_01_27 03:04 h1fw1
2015_01_27 08:57 h1iscex
2015_01_27 09:03 h1iscey
2015_01_27 09:18 h1isiham6
2015_01_27 16:32 h1fw1
2015_01_27 23:42 h1fw0

4 unexpected restarts. Light maintenance day, minor model changes for End ISCs and ISIHAM6 which did not require DAQ restart. Conlog frequently changing channels list attached.

I opened the gap between the bundle of copper pipes that were again rubbing on the ITMy optical lever TX pier causing the 10min-ish sawtooth signal. This is a temporary fix, but is more stable than the first time we saw this. It is in the planning to reroute the pipes and fix other similar issues with other oplvrs.
Keita ran a new scan verifying the fix.

The OIB was set to commissioning upon my arrival for shift at 08:00. DRMI was still locked. I'm going to try my hand at locking the arm(s) as no one is here working yet.

I touched up the RM suspension controls today. RM1 had been tripping its watchdog often during the engagement of the scripts which use the RMs to center the beams on the REFL WFS.

1. Moved the RLP11 low pass filter into the damping filter banks. This is less aggressive than the 5 Hz Cheby low pass that was there and allows for more stable recovery from saturations. The damping gains were checked; seems reasonable.
2. Turned on the LIMIT for the damping filter banks at 1000 counts. This is similar to what I did with the IM mirrors recently.
3. With the DRMI aligned, I adjusted the alignment biases to center the beam on the REFL_A and REFL_B WFS.

Now, when the scripts turn these on the RMs do not trip and the beams are centered.

We have left the DRMI locked (on 1f), Guardian undisturbed starting around 1:13 AM for seismic performance evaluation.

Sheila, Evan, Rana, Eli, Kiwamu, Alexa

Today we were able to reduce the CARM offset from 800pm to 100pm. We made three major changes to acheive such an offset.

1. We noticed that the sqrt(TRX+TRY) counts into the CM board was only about 100 pk-pk. We increased this to about 800pk-pk by reallocating some gain. We decreased the LSC-REFL_SERVO_IN1_GAIN from 0dB to -16dB, and increased the LSC-REFLBIAS_GAIN from 8 to 50.4.
2. We added a z20:p40 to REFLBIAS in order to get more phase and push the UGF of TR CARM from 200 Hz to 150 Hz. This filter is only engaged after we have already turned off ALS COMM, at which point we do not need to compensate for the COMM PLL VCO.
3.  We noticed that ASAIR_RF45_Q was rather noisy as we were reducing the CARM offset. We added an integrator FM2 (z2:p0) to ALS DIFF to reduce low frequency noise. This helped make TR CARM more stable.

Transition Process from 800 pm to 400pm

To start,

• LSC-TR_CARM FM1(2pm), FM9(z35:p1k^2) ON
• LSC-TR_CARM_OFFSET = -0.5
• LSC-REFLBIAS FM9 (z40:p1.6), FM3 (z40:p1) ON, GAIN 50.4
• LSC-REFL_SERVO_IN1 GAIN -16dB
• ALS-C_REFL_DC_BIAS GAIN 28
• TRAMPs at ~13 s

With some TR buildup (approximately 1ct on LSC-X/Y_TR_A_LF_OUT),

• LSC-REFLBIAS FM6 (z1:p0), FM4(z1:p40) ON, GAIN 28.0
• Ramp down LSC-REFL_SERVO_IN2 Gain from 16dB to -32dB then turn off ALS-COMM

With CARM on sqrt(TRX+TRY),

• LSC-REFLBIAS FM10(z20:p40) ON, GAIN 28 at -0.5 cts offset (Note: the gaurdian does up to this point)
• LSC-REFLBIAS GAIN 39 at -1.0 cts offset

Transition Process from 400pm to 100pm

With all the settings as above, we bring the CARM offset to -3.2 (or ~150pm). At this point we transitioned the in-air TR PDs to the IR TR QPD_Bs.  For reference, ASC-X/Y_TR_B_POW_NORM =1,1  and LSC-TR_X/Y_QPD_B_SUM_GAIN = 0.222, 0.175 respectively. Also, the QPD NSUM was about 400cts here. We continued to reduce the CARM offset to -4.5 cts (or ~80pm). At first,t the ASAIR_RF45_Q looked like a decent signal and responded well to a DIFF offset change. We turned on a servo for about 1.5min to ensure ASAIR was around zero (z servo -r LSC-ASAIR_A_RF45_Q_NORM_MON -g -11111 ALS-C_DIFF_PLL_CTRL_OFFSET).  We measured ASAIR_RF45_Q/DARM_IN1 = 3e7 (at this point DARM_IN1 is just ALS DIFF signal). Note: we added a -160dB FM10 filter in LSC-ASAIR_A_RF45. Then the PD_DOF_MATRIX for ASAIR_RF45_Q is 3.3. So far, we were able to transition from ALS DIFF to RF DARM 50% of the way, and then we broke the lock. We started to reconsider whether we were actually in the linear range for RF DARM. Maybe we should be using AS45Q/SQRT(TRX) at this point? This requires a model change; however, this is already impleneted in the l1lsc.mdl that is in the SVN, so we could just copy that.

A little more ...

The farthest CARM offset we reached was -7 cts or ~60pm on sqrt(TRX+TRY) with the QPDs controlling CARM and ALS DIFF for DARM. Here we had 26 x single arm power, and REFL DC dropped from 80mW to ~75mW.

J. Kissel, B. Lantz, H. Radkins

Hugh and I, with the remote advice from Brian, have been investigating the coupling between HEPI differential pressure noise and HEPI platform motion (see preliminary studies in LHO aLOGs 16231 and 16309). In summary, the coupling is smattered between every chambers DOFs, limiting the performance between 0.02 and 2 [Hz]. There's no pattern as to how this coupling occurs except that the coherence for a given DOF happens in a similar frequency band in all chambers. All chambers show differential pressure moderate coherence to HP, but we're still working on estimating the transfer functions between this "pringle" mode and any translations / rotations to assess this impact. Further, we still have set up any successful long stretches of IFO / WFS data for the DRMI, so this pressure noise' impact can't yet be assessed. However, for now, I continue under the assumption that *any* low frequency improvement, especially to RZ / YAW, will improve the relative angular fluctuations of the IFO and stabilize optical gains, etc.

Hugh has already revealed the punchline: this morning's pump-servo OFF data shows that the problem is entirely because is of noise on differential pressure sensor. I'll attach a comment with complete set of plots for proof in a bit.

Further discussion on the noise as it stands with the pump servo (i.e. ON), based on the attached plots, which include

• ASDs of all Cartesian (plus pringle) DOFs' L4Cs -- out-of-loop witness sensors -- compared against the differential pressure and the expected sensor noise**,
• Coherence between all Cartesian (plus pringle) DOFs and the differential pressure,
• ASDs and RMS of Colocated Actuator Drive signals, compared against the differential pressure and the 2 [hr] mean, DC value of each signal,

is below. I post all of these discussion points for future reference and design considerations to show how nastily and diversely imposing sensor noise on the pump servo imposes the platform motion. But mostly, because I sorted through a TON of data and plots to make these conclusions, before we knew the source of the problem.

** For the HEPI L4C ASDs, I plot the *raw* sensor noise because (a) I'm trying to cram as much information on as few plots as possible, and (b) the scale factors for both the IPS and L4Cs are the same for each DOF, and are all between 0.3 and 1.1, so the estimation estimation is off by at most a factor of three. Mostly it's there just to guide the eye, as a primitive noise budget.

(1) Krishna (before coherence between all DOFs and chambers was fully flushed out), suspected that because we now run Z sensor correction is on HEPI, the extra drive force meant excess pressure noise coupling. However, compared to 23e3 [ct_{rms}] range, the Vertical RMS of 5 [ct_{rms}] is peanuts. Further discussion of DC / mean requested drive is below.

(2) Brian suspected that the passive filtering system, the accumulating bladders might not be operating at their nominal air pressure. However, pump 8's (out of 12 for the corner) bladder pressure was checked last week, and was within spec. There're still lots lots to check, but Hugh suspects they're also OK.

(3) I suspect the PID controller for the servo is likely not well-tuned for new differential pressure sensing, suggesting we need to remeasure plant (which could mean significant down time for the IFO). There's been some discussion offline in the SEI group as to how we should systematically characterize the pump servo plant, given there's no "fast" excitation point in the pump servo make a tranditional frequency-response transfer function difficult (see SEI aLOGs 684 and 686). For now, we suspect we can do a sufficient characterization with simple steps using the existing EPICs infrastructure. Characterization to-date (though very early on in aLIGO) was also made by step response (see E1100508), but the assumptions about the plant don't seem sound in retrospect, and were done when the pressure was still on an absolute "single ended" readback.

- Brian's "Allowable Pump Servo Noise" defined in T1100198, but contains a LOT of assumptions. One of which is that the open loop gain transfer function of the feed back loops is "100 at low frequency." As such, Brian suggests, if the HEPI feedback loops are gain limited, try adding some boost at these frequencies to suppress the noise. However, I argue, with Hugh's recent redesign of the controller (see LHO aLOG 15308, the relevant attachment re-attached here), RZ Loops for example have *plenty* of gain, upwards of 3000 - 4000 at 0.1 [Hz], typically asymptoting to a few million a DC. This is far more than Brian assumed, so I thing we're alright in the gain department. Regrettably, the differential pump pressure is an EPICs channel, so I can't get an ASD of the performance above ~8 [Hz], but I'll post more on that in the future comment.

- Differential Pressure Noise supposedly coupling increases with actuator force request, but I've not found this to be true empirically. Check out the table below. Colors of the text help indicate which requested DC offsets are small, and which are large (dark green is smallest, then light green, gold, orange, with bright red is largest, in bins of 50 [micro-whatevers] and anything higher than 200 [micro-whatevers] is marked as bright red). Cells shaded in gray show coherence between the differential pressure and the HEPI L4Cs.

There is no discernable pattern:

Here're what patterns I was able to glean from the above table and attached plots:

• Every chamber has a large coherence with HP
• All chambers coherence drops off gradually below ~0.1 [Hz], probably because the measurement is hitting the L4C noise floor. Similarly, the coherence drops off above ~2 [Hz] because the table motion becomes dominated by IPS noise reinjected via the feedback loops
• Pressure is typically coherent between 0.2 and 2 [Hz] in Z, where RZ is typically coherent between 0.02 - 0.2 [Hz] (though note that the sensor noise limitations of this statement from above)
• BSCs have stronger coupling to pressure noise than the HAMs. One might argue this is because the actuators are pushing more (~5 [ct_{rms}] on HAMs, 50 [ct_{rms}] on BSCs calculated down to 1 [mHz]). BUT HAM6 has a huge vertical offset, but now where near as heavy a coherence.
• Input HAMs have no RZ coupling, but output HAMs and BSCs do
• Only HAM2, HAM5, and ITMX have some X & Y coherence with pressure. HAM2 in X, HAM5 in Y (of course), and ITMX in both. All between 0.6-0.9 [Hz].
• It looks like a pretty bingo board, doesn't it? Thanks for reading this far!

- My best guess at this point is that it depends on the intricacy of how the piping is laid out between each chamber and the pumps. But it's only a guess, it's the only thing I know that significantly different between all chambers.

-------------------

DTT templates for this data live here:

/ligo/svncommon/SeiSVN/seismic/HEPI/H1/Common/

2015-01-23_H1HPI_ActuatorDrive.xml

2015-01-23_H1HPI_PumpControllerNoise.xml

The stopband filter we put in the ETMX OL servo yesterday seems to have done the job of preventing the ringups:

In the attached trend of the OLPIT 3-10 Hz BLRMS, you can see the ringup start around 6AM local time this Sunday, the 25th.

Around noon on Monday (1800 UTC), Evan and Alexa start damping the mode using the bandpass filter in the OL PIT servo. They stop around 2100 UTC when the mode is small. It then rings up for the next 7 hours until we turn the stopband filter on.

Then it rings down with a 1/e time of ~4 hours (which implies a bounce mode Q of ~440,000 if nothing else is driving it).

We should make sure to install these on all of the test mass OL servos.

06:30 Cris and Karen into LVEA- esit doors will be open

08:00 restarted digital camera images on FOM5

08:13 Rick, Darkham, Thomas and Nutsinee to EY for P-Cal work. Working close to STS.

08:14 :21, :22 Sensor correction is off @ EY to accomodate P-Cal work.

08:22 Sigg rebooting end station ISC

08:23 Gary moving ISS arrays from optics lab to H@ enclosure. Will be using exit doors from LVEA to accomodate. Sigg approves.

08:30 Cyrus installing new edge router for CDS. GC will be down for a few minutes.

08:34 Christina w/exterminator visiting all points to check mouse traps.

08:34 Hugh into CER

08:48 Cris and Karen to Mids

08:52 Jef to LVEA to get a LASER vibrometer.

09:00 Plumber on site for toilet maintanance.

09:02 Kyle called to infor about 2 Praxxair deliveries today.

09:08 Betsy out to W Bay

09:10 J Kissell ramping down SUS in HAM6 for ISI FE Model restart.

09:15 Restart HAM6 ISI FE Model. All sensor correction is turned off except for EX. No DAQ restaert required.

09:18 HAM6 restored and back online.

09:29 Karen leaving MY.

09:40 Praxxair called to announce arrival

09:44 Gary driving to EY to talk to Rick

10:08 Doug out to LVEA to move copper pipes under ITMY.

10:11 Rick et al back from the end station. Can't run excitations.

10:13 Jeff an TJ back from LVEA.HEPI pump ! needs electrial attention. Hugh will give more detail.

10:30 Jeff B back into LVEA by HAM2 vibrometer.

10:49 Betsy and Janine out of th LVEA.

11:15 Sudarshan to EX

12:00 Jef back out to LVEA HAM2

12:12 Jeff out of LVEA

12:15 Fil and co out of LVEA

12:30 Jim out to LVEA to get some parts

13:45 Kyle and Joe out tp EY mechanical room

14:20 Kyle ad Joe back from EY

15:20 Sudarshan out to EY

15:50 Sudarshan back from EY

JeffK is going to produce a much more extensive result and possibly conclusions but the simple view is here.  I selected a few chambers to look at BS, ITMX and HAM5.  HAM5 is closest to the Pump Stations, HAM1 is certainly the farthest but it isn't unlocked.  HAM2 might be a better candidate but too late, I chose ITMX, the BS is where the pressure sensors are which derive the differential pressure channels.

I looked at all DOFs (not VP) and we see/saw lots of coherence with HP RZ and Z on most chambers.  HP & RZ being the largest.  I show HP, RZ and the oplev YAW and Pitch of the optic on the platform in the attached plot.  The top group is the BS, the middle traces are HAM5 and SR3, and, the bottom group is the ITMX.

Pretty much nothing seen on the Oplevs but the coherence on the RZ and HP loops when the HEPI Servo is on is pretty clear compared to when the drive to the Pump Stations is fixed ignoring the pressure signals.

More Details:  Switched the Servo to Manual state at 1510utc this morning and made one output tweak at 1514.  The Sensor corrections to the BSCs were turned off at 1549--this may come into the spectra toward the ends of these 10 average 1mHz BW measurements.  The current traces are with the servo off and are started at 1515utc.

The servo was turned back on at 1716utc.  The reference traces (dashed) in the plots where started at this time.

My current conclusion from this is the noisy pressure channels is injecting this noise into the drive signal and it is getting to the platform.  We will tune the controller to help deal with this but the noisy signals must be addressed.

Alexa, Elli, Sheila, Rana, Evan

Today we worked some more to make the sqrt(TRX+TRY) handoff more robust.

Now we can pretty reliably complete the transition by hand. We are working on implementing the transition in the guardian.

We have tried to reduce the CARM offset while locked on sqrt(TRX+TRY), but we cannot seem to get beyond 2 or 3 times the single-arm power without blowing the lock. The next step is to go through the CARM reduction sequence more carefully and characterize the OLTF of the CARM loop in this state.

Gain redistribution

As discussed in LHO#16252 et seq., we suspect that the common-mode board has gain-dependent offsets. If this is true, it explains why the interferometer can be knocked out of lock while ramping down or turning off ALS COMM.

To boost the CARM loop's immunity to these offsets, we redistributed gains as follows:

• The gain of the ALS COMM input on the common-mode board was increased from −4 dB to +16 dB (LSC-REFL_SERVO_IN2GAIN). Correspondingly, the gain on the AO into the IMC board was reduced from +16 dB to −4 dB (IMC-REFL_SERVO_IN2GAIN).
• The input matrix gain for the slow path out of the IMC board (going into the digital CARM control) was decreased from 1 to 0.1 (LSC-PD_DOF_MTRX_5_26).
• The digital gain for sqrt(TRX+TRY) was increased by a factor of 10 (LSC-REFLBIAS_GAIN was increased from 0.8 to 8).

Even with these changes, success is not guaranteed. The gain steps can be heard very clearly when listening to LSC-CARM_IN1, and turning off ALS COMM on the summing board will blow the lock about half the time. We can get better results by using the gain slider on the common-mode board, but we can still hear the gain steps.

Modified handoff procedure

• In LSC-REFLBIAS, we engage FM3 (1 Hz pole, 40 Hz zero) and FM9 (1.6 Hz pole, 40 Hz zero). The gain is 8 ct/ct.
• In LSC-TR_CARM, we set the offset to −0.5 ct.
• We engage the sqrt(TRX+TRY) path on the common-mode board.
• We engage LSC-REFL_DC_BIAS with a gain of 30 ct/ct.
• Once the buildup has stabilized, we turn on FM6 (0 Hz pole, 1 Hz zero). Then we turn on FM4, which undoes FM3. Then we ramp the gain of LSC-REFL_DC_BIAS to 50 ct/ct.
• We ramp down ALS COMM using the common-mode board input gain slider. Then we turn off this input on the common-mode board.

A lockloss plot is attached for an unexplained lock loss during the CARM offset reduction after handing off to sqrt(TRX+TRY). Other lock loss times, all 2015-01-27 UTC: 03:56:53, 04:05:25, 05:36:16, 06:40:59, 07:56:02, 08:37:20. The last four are during CARM offset reduction after the handoff is complete.

For a sqrt(TRX+TRY) offset of −1.5 ct, the gain we need for REFL_DC_BIAS is 50 ct/ct. Our OLTF looks good here. However, when we reach an offset of −2, we seem to lose lock, even though there is no obvious nastiness in the CARM spectrum.

Mystery

Today, locking DRMI without arms was pretty painless. In contrast, DRMI+arms lock acquisition was very, very slow for most of the morning and afternoon. After about 5pm local, it became painless as well. This may have been correlated with our changing the trigger settings to be twice as high with arms (compared to no arms), since the POP18 buildup is twice as high. But we haven't investigated this systematically.