(Alexa, Evan, Stefan, Matt)
The ETMX bounce mode has been limiting us in locking ALS DIFF, and causes us to lose lock when the ESD saturates. The first attachment shows the coil outputs of the stages, and there is a clear peak in the ESDs (note this screen shot was taken with a much lower gain in DIFF and with the boosts off; this peak causes saturation when the DIFF gain is nominal). The second attachment shows the bounce mode appearing in the oplev spectrum. You can see that this mode starts to appear Friday and gets worse into today. Thursday night the mode looks fine, which explains why we were able to lock DIFF Thursday night. At some point Friday afternoon we turned off the ETMX L2 oplev damping; however, we see this mode ringing up before this was switched off.
We managed to damp this bounce mode using the optical lever signal. This has the advantage of not needing anything to be locked, so it is very robust, which is important since it took about 2 hours to damp. The first image shows the L2_OLDAMP_P filter configuration we were using, and a time series of the resulting coil signal. The second image is a trend of the OLDAMP_P_OUT signal, which shows the damping in action (the envelope of the signal slowly decreases with time as the mode rings down, and then jumps up each time we increase the gain). After a couple of hours of damping, we were able to reduce the mode amplitude by a factor of 10, and then return to locking. Note - the bounce mode frequency is 9.775 Hz
I want to give some more detail on the filters we used for the bounce mode damping: We used the ETMX_L2_OLDAMP_P filter, and had only FM1 (0:0.5) and FM6 (Pass 9.8) engaged. The OLDAMP pitch gain was -1.
no restarts reported.
conlog frequently changing channel report attached.
Relieving the arm VCO signals doesn’t work once the COMM and DIFF loops are engaged. (The DIFF loop will fight against the HEPI feedback for example.) Therefore I made a similar HEPI offload servo for the COMM loop.
I use MC_F as the error signal and feed back to the common end station HEPIs.
guardian code:
class HEPI_RELIEF(GuardState):
@fault_checker
def main(self):
servo_gain = -.3
offset_ramp_time = 2
offset_chan_1 = 'HPI-ETMX_ISCINF_LONG'
offset_chan_2 = 'HPI-ETMY_ISCINF_LONG'
readback_chan = 'IMC-F_OUTPUT'
ezca.write(offset_chan_1+'_TRAMP',offset_ramp_time)
ezca.write(offset_chan_2+'_TRAMP',offset_ramp_time)
self.hepi_servo = cdu.Servo(ezca,offset_chan_1+'_OFFSET',readback=readback_chan,gain=servo_gain,control2=offset_chan_2+'_OFFSET',gain2=1);
@fault_checker
def run(self):
self.hepi_servo.step()
return True
attached file shows servo with wrong sign, then sign flipped. Then an unrelated lockloss.
So right now when just the arms are locked on ALS, they each feed to their own hepi. At some point the ALS_COMM guardian turns on the HEPI feedback and the arms turn off their feedback.
One last thing to mention: These offsets will walk away over time and should be zeroed periodically. It should probably be written into the DOWN state of one of the guardians.
Jeff, Dan, Alexa, Evan, Matt
To illustrate the need-for / effect-of the feedback to HEPI from ALS_COMM, I attach two plots.
The first shows the start of an IR lock in the arms. The ALS_DIFF path is turned on about 1/3rd of the way through. Once the differential degree of freedom is out of the arms, the tidal drift begins to dominate the ALS green control signals, and the VCOs run away. The rail at 7V in end-X is where we lose the lock.
The IMC control signals
In the second image, I plot a series of locks around the time when Nic implemented his ezca servo code. After some missteps for gain tuning the offloading of the COMM signal to HEPIkeeps the VCO in range.
Nic's code uses MC_F, but for a permanent digital implementation we think that MC_L is a better choice. The current plan is to add a PCIE channel to the LSC front-end module to send MC_L (the input of the LSC-MC filter) bank to the endstation HEPIs.
(Sheila, Evan, Dan, Kiwamu, Stefan, Alexa)
We were able to lock DRMI + arms off resonance a few times tonight, but the alignment was not great and we would mode hop and lose lock. The guardian is slow to engage the asc wfs, which usually help save the alignment and get the ASAIR build-up high. We need to take a look at our guardian script to get them to engage faster. We did not get a chance to try bringing the offset in and transitioning to TRX+TRY.
The other problem is that DRMI + arms off resonance takes a while to lock (around 20 min), and ALS DIFF is not staying locked for much longer than that. Nic and Sheila worked on a HEPI offloading script (see Nic's alog). However, by the time we got this up and running, ALS DIFF was not locking robustly. For one it seemed we had rung up the bounce mode at 9.8 Hz, which makes locking much more difficult. Another thing we noticed is that the ETMX oplev is glitching.
Of course, as I write this alog, ALS DIFF has been locked for 8 minutes ... unclear what changed.
Nic and Sheila ran Jim's script to run the overnight sensor correction test.
In these two weeks I optimized few times the IMC angular offsets, in order to reduce the coupling of beam jitter to intensity noise. Attached the MATLAB script I used to decide the optimal offsets. It grabs a period of data (of the order of some tens of minutes) and plot some scatter plots of how the band-limited RMS of intensity noise (measured with IM4_TRANS) depends on the IMC angular DOFs. The script parameters are set at the beginning, and the attached one shows the typical values I used.
The typical result is shown in the attached picture. In this case one can see thay intensity noise tends to be samller for positive values of DOF_1_P and negative values of DOF_3_P. My conclusion would be that we need to add an offset of about -20 on DOF_1_P and about 2e-3 to DOF_3_P. I didn't want to interfere with the ongoing locking activities, so I didn't add those offsets now.
We noticed that at least three times tonight, DIFF lost lock because of glitches in the ALS (Y) refl control signals. The times were 0:18:12 UTC, 1:35:00 UTC, and 1:47:29 UTC, we didn't investigate all of the DIFF lock losses we had tonight so there could have been other examples. The glitches were both more frequent and larger in the Y arm, but there are also glitches present in the X arm (they are independent glitches in the 2 arms). We see the glitches even without ALS DIFF and COMM locked, they aren't in the optical levers, the PZT signals, or a number of other things we looked at.
Evan and I drove down the to Y end to look on a fast scope at the glitches. By the time we got down there, the glitches had largely stopped.
07:03 Karen cleaning in LVEA 08:11 Jeff B. and Andres to LVEA west bay 08:23 Jeff B. and Andres back 08:41 Jeff B. and Bubba to LVEA to look at container 08:43 Filiberto and Aaron to end Y to work on PEM 08:52 Cris checking mid and end stations for cleaning 08:56 Jeff B. and Bubba moving storage containers in LVEA (no craning) 08:57 Travis to LVEA teststand to work on suspension 09:21 Keita to end X to work on green WFS 09:32 Jeff B. and Bubba done 09:32 Travis done 10:10 Cris done 10:40 Jeff B. turned on dust monitor 10 (under cleanroom for 3IFO work) 11:02 Gerardo to H2 PSL laser enclosure to work on OFI 11:09 Cris dropping off frocks at end X 11:22 Bubba taking U.S. Linen to mid and end stations (not in VEAs) 11:25 Keita done 12:04 Hugh and Jim W. checking boards at ITMX 12:13 Filiberto and Aaron done (also labeled cables at end X) 12:25 Hugh and Jim W. done 12:25 Gerardo done 13:48 Corey looking for cables in squeezer bay 14:06 Corey done 15:02 Gerardo back to H2 PSL laser enclosure to continue work on OFI
Sheila noted a while ago ITMX was having weird CPS trips. Hugh and I went out during lunch and checked all of the chamber CPS cable connects as best as we could, but we didn't find any loose cables. Some of the the corner 1 cables (over the TCS table) are missing nuts, but the power boards are all secure on all 3 racks, and all cables seem to be well connected otherwise. On Tuesday, we plan on going out with a Genie and look at fixing the missing connectors on corner 1, if possible.
While commissioners were MIA this morning I took the time to try sensor correction at the beam splitter again. Previously, I had found that it pretty much just made stuff worse, at least when I tried HEPI Z. Unfortunately, that still seems to be the case. This time I tried HEPI Z, and ISI X & Y, and in every case it just made things slightly worse. My attached plot shows a comparison between the ISI X for the BS (red) and ETMX (blue). Sensor correction is off for the dashed traces, on for the solid. ETMX shows our expected improvements, but the BS gives no joy. Also interesting that the BS doesn't seem to be performing as well as the ETMX generally, but the mechanical and controls configurations are quite different. I've talked to Hugh, and the input and output matrices have errors on the BS (not on ETMX), and the STS2 the BS uses is a little wonky, it reads ~2000 cts, while the other cornerstation seismometers are in the hundreds. The STS spectra all look similar in the .1hz and above region, but they disagree a bit below, see my second plot. When I get a chance, I'll try using a different seismometer, but I'm pretty sure I've gotten positive results at ITMX using the BS seismometer.
K. Venkateswara
It looks like you may have the sign of the sensor correction wrong. It looks like you are adding instead of subtracting the ground, hence the result looks a factor ~2 higher. Have you tried the opposite sign?
In an attempt to improve (?) previous TF data from QUAD 07, today I checked the cabling connections to both chains and added wipes around connectors that were touching the structure/test stand. I then retook the RO R TF (which showed an unexpected DC offset). The results showed no improvement and looked identical to the previous round of measurements.
I also swapped an L2 AOSEM that was showing low counts and retook spectra for all stages.
Attached are the spectra for QUAD 07. L1 and L2 flags are not aligned.
Alexa, Shiela, Nic
We forgot to post this yesterday ...
Our ASC offloading script had offloaded the wfs to the offset of M2_LOCK_P/Y. Once we ran the script, we noticed that we kicked SRM because SRM is under an offloaded hierarchy, whereas PRM is distributed (BS is also offloaded, but we never feedback to MO P, Y so these filters are off). Looking through all of the optics that we feed back to, only PRM is left under distrubted control, so we decided to swtich PRM from distrubted to offloaded. Our length control scheme for PRM is the same for both these configurations, so this transition was smooth.
We also modified the ASC offloading script to offload the wfs to the M2_DITHER offsets. This signal is always on and is not sent to another stage, so should be okay now.
Removed the following channels: H1:ALS-C_COMM_VCO_TUNEOFS H1:ALS-Y_CAM_ITM_PIT_POS H1:ALS-Y_CAM_ITM_SUM H1:ALS-Y_CAM_ITM_YAW_POS These have been added to the exclude list.
Bubba and I have stabilized the LVEA and VEA temperatures.
We still have known mechanical issues which are probably impacting the control loops so we should be able to improve things - especially XEND.
The one degree spike at XEND on the 19th was due to my attempt to outsmart the system.
Motorized variac heater controls are being ordered for the two end stations which should allow for better control and transient behavior.
We may be asking to raise the set point at XEND - so if anyone has thoughts on this please let us know.
On the evening of the 19th commissioners noticed large angular drifts on ETMX, see alog 15193. The attached plot shows temperature in end X over the past 3 days as well as the optical lever readouts. There is a clear correlation between temperature and optical lever readouts. The trace of the 0.8 C excursion on the 19th in the optical levers is obfuscated by several re-alignments of ETMX. One might wonder, if the optical lever temperature fluctuations correspond to actual optical alignment changes, or if they are just an optical lever feature. Since large alignment drifts were reported on the 19th, one might suspect the former.
Alignment changes of the order 0.5–1 µrad will require a re-alignment of the arm cavity.
Looking at a trend from 3 weeks ago shows that the temperature is now oscillating with a ~2.25 h period and an amplitude of ~0.15ºC.
Here is an LLO alog describing a measurement of the angular misalignment when their HVAC system was shut off. One can deduced a temperature dependency around 35 µrad/°C in pitch, see alog 13817. Yaw seems relatively stable. With a requirement of 0.5–1 µrad the temperature stability would need to be around 0.02ºC.
The other thing noteworthy is that it takes less than an hour for the vertical position to turn around after the HVAC system was engaged. This would indicate that the dominant thermal coupling is radiative through the chamber walls, and not conductively through the ISI. The reaction time of the ISI is of order 36 hours—which could be responsible for the long tail seen in restoring the position.
The calculation made by Brett in the above referenced link, as well as the measurements of pitch vs temperature that are reported by Stuart A in the LLO log, correspond to the pitch of the TOP mass of the quad suspension. According to the suspension model, the test mass pitch is 25% of the TOP mass pitch. So, the 30-40 urad/C for the TOP mass translates to 8-10 urad/C for the test mass. So 1 urad corresponds to 0.1 C. Still quite sensitive, but not so bad.
Not sure, if this still agrees with the observed optics drift. If I interpret the plot in alog 13639 correctly, the HVAC system was off for about 20 h, in which the temperature was rising by ~3.2 F. Assuming a linear trend we get 90 mK/h, or 15 mK in 10 minutes. The optics was drifting 0.5 µrad in 10 minutes. So, we get ~34 µrad/K at the optics.
On the other hand, looking at the temperature oscillations in EX we would expect to see 10 µrad-pp, but only see 1 µrad-pp. A time constant of ~1 hour would correspond to a pole frequency around 50 µHz which is abount 2.5 times slower than the observed oscillation. Assuming this leads to an attenuation of 8 dB, a reduction of 25% through the suspension chain would explain what we see in the optical lever.
There has been some concern that there might be excess cps noise in some of the channels. So i looked at 20 minutes of data at 1am sunday night/monday morning.
Looking only above 30Hz where the sensors have hit the noise floor, all of the coarse channels are similar and between 3.5-4.5E-10m/rrtHz about what we expect.
The stage 2 channels show two outliers, ITMX H2 and ITMX V1, maybe BS H2 also but that is close enough so that it could just be at a large offset (we expect the noise floor to go as the gap squared) I'll check that.
The first thing to do is for me to look at another time, and to check the cables and connections for those sensors
I looked at a second data set calling it "B" (24 hours later) ST2 ITMX H2 and ST2 ITMX V1 still show excess noise BS H2 is down to 4.5-5E-10m/rtHz which is a little bit noisy, but probably within what we are calling acceptable. I attached the data because Jeff asked to see the ADC noise on the plot
When I say large offset I mean > 10000 counts, so 1200 counts is centered for this discussion
ITMX Stage2 H2 & V1 CPS offsets are 900 & 3800 counts. While V1 is actually the largest offset of all the BSC CPSs, H2 is 21st of 30 (towards the bottom) of Stage2 CPS offsets. At 1200cts, BSC2 H2 ranks 17th of 30. So the offset maybe an issue for ITMX V1 but the others...? And, what about ITMY V1 at 3700 counts and ITMX V3 at 3200?
Attached are all the BSC medms showing the offsets.
Some additional info regarding the CPS - On the figures are plotted time series, integrated RMS, and ASD down to low frequencies. Somme comments:
- At high frequencies, not much to add on sensor noise (ITMX and BS both have two CPS untis with elvevated sensor noise on Stage 2). I looked at data of the Nov 17th, 18th and 19th, and get similar results.
- All Stage 1 CPS units are within 1um p2p, except BS horizontal that is moving 4 times more. Something to look into.
- At the microseism, the three vertical sensors are moving in sync, on all stages of all platforms. Probably normal (the platform is inertially decoupled down to the micro-seism with th 90 mHz blends)
- The low frequency motion amplification is about 100 times larger in the vertical directions than it is in the horizontal directions.
The 5 figures in the previous log are for data ten on the 17th at 3pm PT.
Results and comments are similar for the 18th and 19th, except for ETMX (attached plot) that shows different behavior at low frequencies, as expected with the sensor correction that was turned on Tuesday. It also shows features on Stage 2 at the SUS resonances, that might need to be doubled checks.
Could this be related to the trips on ITMX? (alog 15021)
this log seems to have gotten hijacked
I check the HAM-CPS and they all seem to be good at high frequency
New SR3 offset: [452.9, -155.3].
There could be +-120-ish measurement error for YAW due to difficulty in finding the PR2 baffle right edge, so later if somebody gets suspicious about the clipping finer YAW scan of SR3 might be a good idea. This problem is not present for PIT.
New SR2 offset: [2800, 800].
Tolerance is +-100, but the center value strongly depends on the SR3 offset.
Since Doug is not available for finding the SR3 oplev beam with new offset, and since we use SR3 oplev for damping, we reverted SR3 and SR2 back to the original angle.
Tomorrow morning SR3 oplev will be done with Doug.
Plots will be posted later.
SR2 [2963.7, 2728.0]. SR3 [430.3, 142.6].
Centered AS_C using SR2 offset: [2917. 7, 2794.0].
At this point ASC_SUM was [1576.29, 1576.87] (measured twice, each is 10sec average number).
Position 1: [3042.9, -438.4].
Position 2: [-2137.1, -408.0].
Center = (Pos1+Pos2)/2 = [452.9, -423.2].
Then moved the beam to the right edge.
Position 3: [452.9, -1248.4+-100]. Barely touching.
Position 4: [452.9, -1848.4+-500]. Totally blocked.
For whatever reason YAW is much more ambigous than PIT to my eyes, and right edge is more difficult than top and bottom.
Right = (pos3+pos4)/2 = [452.9, -1548.4+-510].
Center-Right = 1125.2+-510 in the slider counts. This is supposed to be 36.75mm.
SR3-SR2-SRM angle is 1.67deg, and the baffle-SR2 distance seems like about 46cm (eyeballing HAM4 systems drawing), so the beam distance at the baffle is 17.5mm.
New beam position = 17.5mm/2 =8.75mm to the left of the center.
Y=-423.2 + 8.75mm/36.75mm * (1125.2+-510) = -155.3 +- 120;
NEW SR3 slider = [452.9, -155.3+-120];
At this point SR2 was moved to [2708.7, 814.0] to center AS_C, and the SUM was found to be [1596.99, 1597.84, 1596.48] (three measurements), this is about 1.3% increase from the initial number (but note below about the interference pattern caused by either some etalon effeft of a ghost beam from somewhere).
Scanned SR2 in YAW, then in PIT, to find the Faraday edge while centering AS_C using Pico.
Today I made a finer scan than previously done (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=15023) and what I originally thought to be a ghost beam looked more like an etalon type interference that mostly depend on the beam angle on AS_C. It was mostly in YAW but you can also see it in PIT, and the pattern is very repeatable.
Anyway, my objective here is just to place the beam at the center of the Faraday aperture, and I chose this:
New SR2 slider = [2800, 800].
The peak-to-valley in YAW data is as large as 1.5% or so. Does this mean that SR3 scan before/after comparison is useless? No.
During SR3 scan, the beam was shifted by 300 counts in YAW, or about 10mm on SR2. The beam pointing on AS_C was fixed using SR2, so the beam angle on AS_C changed by about 10mm/18m or so, i.e. about 600urad or so.
OTOH, the full scale of the SR2 YAW scan corresponds to the Faraday aperture of 20mm, and that's roughly the beam shift on the pico. The beam position on AS_C was fixed using pico, and pico-AS_C distance is about 14 inches, so the beam angle change over the entire SR2 YAW scan is 20mm/14" = 60mrad or so. This is three orders of magnitude larger than SR3 scan angle change.
If we replotted it as the function of beam angle on AS_C (which I didn't), and put both the SR2 scan and SR3 scan data on the same plot, two data points representing the before/after SR3 scan would be basically on one vertical line in the plot. If this is indeed an etalon type thing on the diode surface, basically SR3 before/after the beam would see the same interference. That's my theory anyway.
Here is a collection of suspicious CPS trips on ITMX. This is a problem only on this chamber, which has just cropped up in the last few weeks. It needs to be investigated.
another example
Still there, still a problem....
I made a few plots today. The spectrum of the CPS right before and right after the trip, and the zoom-in time series plot around the time of the trip. I notice that the time that the CPS signal goes down does not match the GPS time indicated the trip exactly (off by a few hundred milliseconds). While making the spectrum I also notice the peak near 4Hz in the "beforetrips" spectrum plot. So I went and look at the LHO summary page and found that there's a small gaussian-looking bump around 4Hz that seems to appear everyday. Probably not very important but just wanted to point that out. Also, please note that V2, H2, and H1 signals are almost perfectly overlapped (that's why you only see two colors). I'll start looking into other related channels that *should* have seen the signals. Although I believe this might be an electronics issue.
Ran a first set of TFs for 3IFO-QUAD09. The undamped plots look OK (pitch is a bit off). The damped plots measurements do not match the model between .1 and 20Hz very well, for both the Main and Reaction chains. Will investigate the cause. Plots are attached. As Betsy noted in aLOG 14128 the second pitch mode shift is present as for the other 3IFO Quads tested to date. All files, plots, and scripts have been commited to SVN.
Spectra for this quad attached.