Per work permit 5741, continued with the modification of the SUS SAT Amps. All units for EX, EY and HAM4 were completed today. See LHO aLOG 25685 for status of corner station.
J. Kissel, C. Gray Corey grabbed the belated charge measurements for this week. The results are attached. The message: the bias flip appears to have worked as expected, and the bias voltages are slowly creeping back to zero. This is the first effective bias voltage measurement since both bias flips on Feb 16th (the last measurement was the day before, Feb 15th). Recall after the last flip, the first few measurements we're a good indication of the eventual rate of charge / discharge, so we should continue to get weekly measurements. (And now one *more* operator knows how to do it!) Two bits of sadness: (1) the calibration line amplitude monitors are no longer computed. That means we can't make the continual assessment of the longitudinal actuation strength like we'd done during the run, see e.g. LHO aLOG 24547. I'm gunna ask Greg why, and if we can't restart it. (2) Since the ESD Driver's response has changed with the deployment of ECR E1500341 on Feb 9th (see LHO aLOG 25468), the DARM loop model no longer agrees with reality, as was discovered after the bias flip -- see LHO aLOG 25604. In the rush, we gave up, didn't fix the model, and therefore didn't update the EPICs parameters that are used by the GDS pipeline calculate the time dependent actuation strengths. That means that there is no new reference time, and the pre-O1 reference time of Sept 10 2015 is still being used. Maybe that's good, maybe not. Depends on what questions you want to ask. "Reconciling" these optical lever effective bias voltage measurements with the recent measurements of EY ring heater voltage coupling to charge *on the barrel of test mass* (see LHO aLOG 25655): (1) Measuring the ring heater's coupling to the charge on the barrel of the test mass is *not* necessarily the same charge that the optical lever measures, which is between the gap. See discussion in T1500467). (2) Further, having the bias voltage ON at 400 [V] during the EY measurement (see later comment LHO aLOG 25669) will certainly confuse the results. Changing ring-heater potential (the ~ few [mV] drive at 162 [Hz]) is attracting the reaction mass bias ring instead of the test mass charge along the barrel. With the now-moving reaction mass having charge as well (in between the gap, as measured by the optical levers), then one can imagine a good bit of confusion between all of the different mechanisms for charge to change the actuation strength (again, see discussion in T1500467).
Position update: STS2-B and STS2-C are in the BierGarten. They are about a meter apart. Jim is using STS2-C for all corner station sensor correction. STS2-A was moved to the Yend for buried use but it would not center. Robert replaced it with the PEM unit and I put the STS2-A back in the LVEA near HAM2. It currently does not have the igloo in place.
The lack of thermal isolation is evident in the attached plot where the HAM2 blue traces all have much larger low frequency magnitude. Otherwise, the common factor in the coherence plots suggest that HAM5 STS2 is the only unit running well on all axes.
I have lowered the HAM2 unit just now 2330Z so the igloo would fit. It will be several hours likely before it stabilizes. I'll look again at it Monday.
It took many centering attemps but it looks like the STS2-A at HAM2 is now nicely centered. With the igloo just installed though, it may drift as things warm up in the igloo.
TITLE: 2/26 DAY Shift: 16:00-00:00UTC (08:00-04:00PDT), all times posted in UTC
STATE of H1:
Overall Summary:
On the plate today was HWS work (this was most of the shift) & OMC noise/noise hunting in the PM. In parallel to the HWS work, we had the ETMX Sattelite box mods performed, and also did charge measurements on ETMy & ETMx. I also started some investigations for why arm powers drop during DRMI ON POP (this was something Sheila requested)....handed this over to TJ.
Shift Activities:
1505 - 1525 hrs. local -> To and from Y-mid LN2 at exhaust < 1 min after 1/2 open LLCV bypass valve. Next over-fill to be Sunday, Feb. 28th before 4:00 pm local.
Jim & I shifted the instrument back to the 40m hole. It was not reading centered still when we left it at 1030PST but when I went back at 1200 all legs were reading under 1V. There was one leg at 0.9 so I centered the masses again but it was still at 0.9V ten or so minutes later. I may need to tweek the level to change this but action level is +-1.5 or 2V depending on manual source. So, I deem the seismo ready to use and that time starts at 2100 utc 26 Feb.
TITLE: 2/26 DAY Shift: 16:00-00:00UTC (08:00-04:00PDT), all times posted in UTC
STATE of H1:
Quick Summary:
H1's been locked for the last 4.5 hours, BUT I just broke lock (took IMC Guardian to DOWN), so that Filiberto could do work on HAM4's SR2 SUS Sattelite Box.
LVEA is Laser HAZARD.
Environmentally, we have looked good with low useism/winds & no earthquakes.
Chris S. is 200yards down the Xarm for beam sealing work.
TITLE: 2/26 eve Shift: 00:00-08:00 UTC (16:00-00:00 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
QUICK SUMMARY: Commissioning work as usual.
LOG:
Jenne, Sheila, Hang
We worked on engaging the 90 MHz centering loop tonight.
We first locked the ifo in the DRMI_LOCKED stage using the old DC centering loop. Then we opened the centering loop and the src1 loops and adjust the phases for the 90 MHz WFS. The procedure was that we first adjusted each seg. individually such that the length signal showed in I phase of each seg., to fix the relative phases between quadrants, then we drove a line by exciting one of the OM mirrors pitch (yaw) and rotated the overall phases of 4 segments together so that the pitch (yaw) signal showed up in I phases. By doing so we were able to switch to the 90 loop and lock the ifo stablely. We could also directly lock the ifo to DRMI_LOCKED stage with this 90 MHz loop.
The new phases of the 90 WFS are:
| seg. | 1 | 2 | 3 | 4 |
| A | 19 | 58 | 44 | 49 |
| B | 62 | 81 | 76 | 91 |
However, we somehow kept lossing lock at the DRMI_ON_POP stage with the 90 loop.
We then measured the sensing matrix at DRMI_LOCKED stage, and the results were
| Optic | WFS | [ct/ct]; 90 MHz centering | [ct/ct]; DC centering |
| BS | AS_A_36 | 3.47e-2 | 2.40e-2 |
| BS | AS_B_36 | 3.56e-2 | 3.00e-2 |
So the gain increased by ~20%-40% by using 90 instead of DC centering.
We thought this was the reason of lock loss, but after decreasing the gain digitally by the same amout, we still could not proceed beyond DRMI_ON_POP. The problem remains unknown.
Nutsinee, Aidan, Den
We have looked at the temperature data during O1 with the goal to estimate coupling of the temperature fluctuations to DARM. Coupling mechanisms include radiation pressure, thermal expansion of the optic and coating. We took numbers from Stefan Ballmer's thesis and Aidan's notes for these coupling mechanism. The total coupling coefficient is
DARM = 2 × 10-10 RTN / f, where RTN is relative temperature noise.
We measured in-vac and in-air temperature noise using TCS sensors. Attached plot shows the result of the measurement. Above 10mHz sensors are limited by electronics noise. We used spectrum analyzer to avoid ADC noise but this did not help much, electronics noise of the readout circuits still limit the measurement at high frequencies.
In-vac sensors are limited by 1/f electronics noise. But for an upper limit we can assume temperature noise of 5 × 10-1 (10-4 / f) K/Hz1/2 . This projects as 1/f2 noise in DARM with ASD of 2 × 10-20 m/Hz1/2.
The actual coupling coefficient is probably lower since one might assume that in vacuum temperature fluctuations should be smaller compare to in-air fluctuations. On a 24 hour scale in-vac flucuations are a factor of 2 smaller, compared to in-air fluctuations. In-air sensors have less noise and at 1mHz measured fluctuations are a factor of 3 lower compared to in-vac measurement. Tacking this into account we can assume that vacuum sensors overestimates temperature fluctuations by a factor of 6 above 0.01mHz.
The basis for the temperature fluctuation transfer function is outlined in the attached calculation.
Updated the corner Beckhoff code to incoporate the tidal servo engagement delay and the new EOM driver readback calibration.
Does this tidal servo engagment delay also need to be propagated to the end stations? We have had the same problem tonight that was described in 25695
Evan, Den
Tonight we asked ourselves a question whether 1/f (or 1/f^2) noise, seen in DARM around 100Hz, comes from the OMC or not. We put a bandstop filter to the DARM control loop at 92-127Hz and made a correlation measurement between AS 45 WFS SUM and OMC PDs at this frequency band. The idea is that if there is any OMC noise coherent between 2 OMC PDs, it should not be present at the RF detector.
Attached plot shows the results of the measurement. Cross-spectrum between WFS and OMC PDs around 100Hz is almost the same (15% lower) as cross-spectrum between two OMC PDs. We integrated for 3.5 hours and AS 45 WFS SUM channels are not DQ. We can significantly improve the measurement if we record these channels and integrate for ~20 hours.
At the current precision of the correlation we can not say that noise around 100Hz comes from the OMC. Right now it looks vice versa.
We have also measured coherence between DARM and voltage noise of +15V signal going into the vacuum. Noise level is 2uV/sqHz at 100Hz and coherence is <10-3. This noise is insignificant for the current sensitivity.
Den, which +15V signal is this that you measured?
Rich, we have measured the noise on pin 6 (+15V head 1, D1300502). This noise is highly coherent with noise on pin 2 (+15V on head 2) and partially coherent (0.4) with noise on pin 7 and 3 (-15V, head 1 and 2). For this reason, we did not measure DARM coherence with other pins.
Today Keita and I spent some time thinking about OMC length noise, there will be an update coming soon with more information and a noise projection.
We spent some time looking at some nonlinear behavoir noise in the drive to PZT1. Our dither frequency is 4100 Hz, and looking at the low voltage PZT monitor we can see a small 8 Hz and a larger 16 Hz comb. There is also other non stationary noise in the monitor, and a broad peak at 12.7 kHz. We have moved the dither line frequency to 4100.21 Hz, so if this was the cause of the 16 Hz comb in DARM we would now expect it to be more like a 16.84 Hz comb. Evan Goetz tells us that we need 15 minutes or more of data in low noise to evaluate if this has changed any combs in DARM.
We have just reached nominal low noise at 3:14:34 UTC Feb 25th, although the low frequency noise (below 50 Hz) is worse than normal. I've temporarily changed the dither frequency in the OMC guardian, so if there is a longer lock later tonight it should also have this changed dither frequency. (If anyone wants to double check what the dither frequency is, the channel is H1:OMC-LSC_OSC_FREQ
To quote Bill Murray in Groundhog Day, "Anything different is good." (at least in this context) The 16-Hz comb does indeed appear to have changed into a 16.84-Hz comb. A DARM spectrum from two hours (400-sec coherence time) last night in the 150-250 Hz band is attached, along with one from January on a day when the 16-Hz comb was strong. New lines are seen in this band at 151.56 Hz 168.40 Hz 185.24 Hz 202.08 Hz 218.92 Hz 235.76 Hz Some 1-Hz zooms are shown for a couple of the new lines. So...can we fix this problem?
Keita, Sheila
So that we can keep the OMC dither small while driving a reasonable level of counts out of the DAC, we added a voltage divider (somewhat creatively built) to the D-sub from the DAC to the driver chassis. This is a 11k/110 Ohm divider on pins 1 +6. We have increased the dither amplitude from 6 cnts to 600 cnts, so the round off errors will now be 100 times smaller compared to our signal.
The attached screenshots show the PZT1 AC monitor before and after this change. The lines below 1 kHz are always there, (even when there is 0 coming out of the DAC) and are not present on the analog signal coming into the driver chassis for the monitor.
We have reverted the frequency to 4100 Hz. If we get a long enough low noise lock tonight we can hope that the 16 Hz comb will be better. If things look good we should upgrade our voltage divider.
Thing is, our dither line used to be 12 counts pk-pk, so the rounding error was actually significant (signal/error ratio is something like 10 in RMS), and the error showed up as lots of lines because we're sending in only one sinusoidal signal. These lines actually drive the PZT length.
Making the dither bigger, the round off error RMS doesn't change much so RIN will become smaller.
We inserted two sets of 11k-110 Ohm resistive divider, one each for positive and negative input of the low voltage pzt driver input because it was easy. This is a temporary non-solution. A permanent solution is TBD.
The first attachment shows the spectrum of the DAC IOP channel for the dither, i.e. the very last stage of the digital, before we increased the amplitude. RMS of the forest of lines is about a factor of 10 below the RMS of the dither.
The second plot is after increasing the amplitude by a factor of 100, the rounding error RMS is still at the same level though you cannot tell from the plot, the dither to error RMS ratio should be more like 1000 now.
Three large lines in the second plot are not round off errors but imaging peaks that were previously buried in the round off errors: 12283.8kHz=16384-4100.2Hz, 20484.2Hz=16384+4100.2Hz, and 28667.8=32768-4100.2Hz.
Actually, the dither line is still at 4100.21 Hz for tonight, (I had forgotten that I put this into the guardian). We will revert it tomorow.
Splendid -- no 16-Hz or 16.84-Hz comb seen in a 2-hour stretch from last night! See attached spectrum 150-250 Hz spectrum for comparison with above plots, along with 0-1000 Hz spectra from last night and from the night before, with the 16.84-comb present. Many thanks from the CW group as we look ahead to O2.
Sheila pointed out that the noise floor for the 2nd spectrum is considerably higher than for the 1st and could be hiding residual lines due to the dither. So I tried shifting the 2-hour time window a half hour earlier, to avoid the hellacious glitch seen in the inspiral range (see 1st figure) near the end of the original Feb 26 interval. The 2nd figure shows the resulting spectrum with a noise floor closer to that on Feb 25. The 16.84-Hz comb still does not appear. So I think it's safe to say that the 100 times multiplication / divide trick did indeed suppress the 16.84 Hz (originally 16 Hz) comb a great deal, but of course, we will need long coherence times and long integrations to see if what's left causes residual trouble for CW searches.
Per work permit 5741 began the process of modifying all Suspension Satellite Amplifiers. Drawing D0901284-v4 calls for the addition of Cap C601(10uF) and C602 (.1uF) between the -17V to Ground around U503 the Negative Regulator VEE1. Today with Ed M. Soldering away in the lab we were able to complete all of Han2 units. Complete are: MC1, MC3, PRM, PR3, MMT1, MMT2, SM1, SM2 All Stages. We did have a problem with two Sat Amps. One shared between MC1 and MC3 and the one for MMT2,a trace blew when it was powered up. So replaced SN 1100117 with SN S1000287 and SN1100068 with SN1100066.
Tracking Names: SM1 = IM1, PMMT1 (MMT1) = IM2, PMMT2 (MMT2) = IM3, SM2 = IM4
UPDATE:
As of today all HAM3, HAM4 and EX Amps have been modified. HAM2 amps will have to be re-addressed due to an error in installation of the mod. 3IFO boxes are in process.
- Ed
I have subtracted SRCL coupling from DARM, and found that residual noise has the shape of 1/f4-5 at 15-30Hz. I remember when L2 was in acquire state we could see actuator noise in this frequecy band in DARM. For this reason I decided to look into L2 noise again even though actuators are in the low noise (state 3) during current locks.
All 16 actuators show similar noise levels. Attached plot shows spectra for one of them (ITMX LL) in different states. When there is no control signal, actuator noise in low noise state is a factor of 10 smaller compared to acquire state in the frequency range 10-30Hz. However, if a small (few counts) low frequency excitation is applied, then actuator noise increases by a factor of 10. The noise increases almost by the same level if a large excitation is applied. I decided to check if upconversion happens in DAC, actuator or noise monitor. Control signal was shifted by a DC offset (10000 cnts) and actuator noise has reduced by a factor of 2-3. From this measurement one might conclude that DAC is responsible for extra noise. Also, we run oplev servo on the ITMs and even though control signal is aggressively low passed, actuator noise still increases above 10Hz.
Since L2 actuator noise depends on the low frequency control signal (or DC offset), then actuator noise may or may not be coherent to DARM at 10-30Hz. However, when we looked at DARM spectrum with bandwidth of 1Hz, we saw that noise goes up and down by a factor of 1.5 at 10-30Hz.
We have measured the differential actuator noise in low noise by notching ETMX control signal at 20Hz. Spectrum is 0.1 cnts/sqHz and is consistant with the noise when small low frequency excitation is applied (and a factor of 10 higher compared to the case when no excitation is applied). Total noise from L2 is 1.4e-19 m/sqHz at 10Hz and from L1 is 2.2e-18 m/sqHz at 10Hz. This result is consistant to the previous measurement using pringles technique (Chris alog 21070).
Evan, Kiwamu, Den
We measured L2 actuator noise directly from the coils on ITMX. We did not find any irregular noises, current noise looks normal. We have also measured the noise on each coil end relative to the ground. At 20Hz the noise level is 4uV/sqHz. We drive one of the coils in common relative to the ground with 300uV at 30Hz but did not see any noise in DARM.
Kiwamu, Den
Tonight we have shut down ITMX and ITMY L2 drivers while in low noise to double check that these drivers do not cause extra noise at 15-30Hz. We did not see any change in DARM. We would like to do the same test for ETMs.
Den, Kiwamu, Evan
We continued investigations into locking robustness and low-frequency noise.
Notes on robustness:
>> Engaging the soft loops is still painful, particularly in yaw. When the loops are ramped up to their nominal gains (a few tens of millihertz bandwidth), the SRM yaw loop misaligns the SRM in yaw, which causes POP90 to rise and causes lockloss after about 1 minute. If the SRM yaw loop is turned off, this misalignment does not occur. So far, the most reliable way to engage the ASC is to (1) engage the soft loops with the −20 dB filters, and let them run for a few minutes, (2) turn off the SRM yaw loop, (3) turn off the −20 dB filters in the soft loops, and then (4) once the soft loop error points have reached 0, turn the SRM yaw loop back on. This has not been added to the guardian.
>> Den retuned the PR2 actuator feedforward which decouples MICH from PRCL, but this has not been added to the guardian yet.
Notes on noise:
>> Similar to yesterday's frequency noise test, we injected high-frequency noise into the ISS first-loop error point. We drove several volts (both sine waves and broadband noise) up to 10 MHz, but we did not see any nonlinear coupling.
>> As noted previously, the input jitter coupling into DARM is worse than before, particularly in pitch. Den opened the SRM angular loops and moved SRM to minimize the coupling. However, this seemed to make the noise worse in other places. In particular, the region from 35 Hz to 70 Hz swas dominated by some kind of nonstationary excess (perhaps scattering in HAM6). Also, there appeared to be a slight excess frequency noise above 5 kHz.
>> We drove the ITM ring heaters (upper and lower) in common-mode in order to measure the voltage-to-displacement coupling in DARM. By driving a few lines at 250 mVpk between 80 and 160 Hz, we could see that the coupling goes like 1/f2. The levels at 160 Hz are as follows:
| Upper (m/V) | Lower (m/V) | |
| IX | 2.1×10−17 | 4.6×10−17 |
| IY | 0.27×10−17 | 1.0×10−17 |
>> We flipped the sign of the DARM offset. Normally we run with the X arm shorter than the Y arm (i.e., a positive offset is applied at the DARM error point, and DARM is Lx − Ly); so here we are running with X arm longer than Y arm. This is achieved with the ISC_LOCK paramter lscparams.omc_sign that is applied at the appropriate points during the dc readout handoff. The sign of the SRCL feedforward also has to be flipped, and the SRCL FF filters that we normally use cause some 1 Hz instability that unlocks the interferometer. We installed a more aggressive AC coupling filter (FM8), and this solved the issue. DARM has a small amount of excess noise with this new offset, but the SRCL coherence does not seemed to have changed much after FF retuning. Good time to look at is 2016-02-21 21:44:40 (bruco).
Measured coupling of ETM ring heater potential to DARM at 162Hz
| Upper (m/V) | Lower (m/V) | |
| EX | 2.0 ×10-17 | 2.2 ×10-17 |
| EY | 2.1 ×10-16 | 2.3×10-16 |
This measurement shows that EX potential coupling to DARM is similar to IX and IY. However, EY coupling is higher by a factor of 10.
One interesting conclusion is that the coupling of EY potential is similar to LLO (alog 16619) before this TM was discharged. At the same time oplev measurements show small charge on the surface.
Attached plot shows reduction of PRCL control signal when MICH feedforward is running. We actuate on PR2 M2 with gain of 0.24 and assume that BS and PR2 actuators have the same frequency response above 5Hz.
Attached plot shows reduction of input jitter noise seen in DARM after SRC alignment.
We drove IM4 and SRM in angle and measured first and second harmonics of the drive in arm transmission power, POP_DC, AS_DC and OMC_DC. This measurement has shown that PRC and arm misalignment is small (2.3e-3 of divergence angle) and SRC for sideband is also good (0.06 and 0.1 of divergence angle for yaw and pitch), but can be better. Since we could clearly see some misalignment on the camera, we opened SRC1 loop and moved SRM manually by 10urad. SASY90 has increased by 3% and jitter coupling has reduced by a factor of 5. We also noticed that for particular SRM alignments DARM noise increases by a factor of 2-3 in the frequency range 40-80Hz.
Tomorrow we plan to continue investigations on alignment and on potential coupling to DARM.
Higher coupling of ETMY RH potential to DARM is not surpring since ESD bias was equal to 400V during the measurement.
The attachment shows the DARM offset flip test with SRCL control noise removed. It seems that the positive sign is still slightly worse than the usual negative sign.
