Attached are pressure trends from cold cathode gauges from Jan. 2016 to now. The noise level of the gauge seems to be higher since Beckhoff system was installed.
With the long total duration from 0 to full lock it becomes more important to shave off some script run time where possible.
In that spirit I relaxed the tolerances for ASC convergence in CARM_ON_TR, which is just before the automatic WFS relief:
# tolerances retried on 20160713
# wfsTolerancePit = [5,200, 100, 300, 200, 100]
# wfsToleranceYaw = [5,200, 100, 300, 200, 100]
# tolerances from 20160713, intended for speed-up
wfsTolerancePit = [5,400, 200, 600, 400, 200]
wfsToleranceYaw = [5,400, 200, 600, 400, 200]
If the quality of the relief gets worse, we might have to revisit then. (I suspect that the thermal heating at 40W is the bigger problem though.)
The FSS had a hard time acquiring lock and staying locked this morning. I had noticed that the pre-modecleaner
reflected spot looked "mis-aligned". The pre-modecleaner alignment was tweaked up, bringing back the vaguely
familiar reflected spot. The reference cavity alignment was also tweaked up but really there was no substantial
improvement in its transmission.
Whilst the frequency servo was trying to acquire, I noticed that the injection locking relock counter had
jumped from ~3 this morning to over 40. In addition the high power oscillator PZT showed a few discrete level
jumps.
Even with the input modecleaner disabled, the laser frequency was being yanked as can be seen from the reflected
spot showing more than the usual two lobes. I tried re-acquiring the FSS lock at a different NPRO crystal temperature.
Previously the slow voltage slider was around -0.0010. Now it is around -0.2630. I have also changed the locking
search ramp to reflect this. Things seem to be more stable at this operating point - the input modecleaner acquired
lock for a start.
If the FSS lock is reacquired at a slow voltage close to zero and the FSS has a hard time maintaining lock, and
things seem better at a different slow voltage, this could be an age-related symptom of the NPRO. Something to watch
out for.
One could ask why the NPRO PZT and not the high power oscillator PZT. The high power oscillator PZT time series does not fluctuate wildly compared to the NPRO PZT, which is why I suspect the NPRO.
Here are some plots comparing a power up from the end of O1, where we didn't have a significant drop in power recycling gain going from 2 Watts to 23 Watts, to one from last night.
The first plot shows several monitors of recycling gain for the 2 power ups, plotted against time in the middle coumn and input power in the third column. All three monitors of carrier recycling tell the same story: In december the recycling gain didn't drop significantly between 2 watts and 25 Watts, now it drops 6-8% by 23 Watts and 15-16% by 40Watts of input power. The beahvoir of AS90 drops by about 8% going from 2 Watts to 23 Watts, and 15% by 40 Watts, which is not sigificantly different from the behavoir in Decemeber. The power at POP18 drops by 48% durring the power up, we can't compare this to December since the diode was saturated then.
The second plot shows the power on the baffle PDs durring the 2 power ups. It shows that even before we had a bad recycling gain drop, we had a lot of power hitting the baffle PDs.
Ed, Hugh
...at least I'm confident they are. If folks could keep an eye on these occurrences asnd report any foolery to me, for now, I'll assume no news is good news.
JeffB reported the ITMX was found tripped this morning. Pretty clearly it was the arrival of the S-waves ; the platform is already tripped when the largest amplitude, lower frequency surface waves arrive later. The attached trend clearly shows the sharp peaks arriving at the ground STS in the Bier Garten at the moment the Watchdog State goes high. Why the ITMX is the platform that is most sensitive is an ongoing investigation. The earliest arrive P-Wave should be largely vertical (Z) where the next arriving S-Waves will be horizontal. A Clue!!
Tried to do some FSS related measurements to see why it was the FSS kept losing lock.
Unfortunately it seems the FSS fieldbox signals of interest - which is just about all
of them as far as transfer function measurements are concerned - are not of any use
in their current state.
In doing a measurement this morning, the injection locking was broken which in
turn tripped the high power oscillator's power watch dog. The laser restarted without
any issue.
The missing equipment hunt concluded with limited success. There are still a few items missing. Fred, Vern, and Richard thanked all for the efforts. PSL – Looking into an instability with the FSS. CDS – Working on frame writer problem VAC – Will need to bake out the End-Y RGA before O2. All other subsystems report no problem. There will be no maintenance window on Thursday. There will be a safety meeting this afternoon at 15:00.
The ITM-X ISI Stage 1 and Stage 2 WDs tripped at 12:35:25 and 12:35:30 (UTC) respectively. No problem resetting. Was not highlighted on Ops Overview MEDM.
painful - we need to make the relocking robust
To do next: TCS tuning (diff?) see whether the new noise depends on it.
Updated the guardian script to reach low noise in both 25W and 40W mode.
Attached is a DCPD cross-power spectrum at 40W (references) and at 25W (live data). Red is the PD_A-PD_B cross power. Blue is the DCPD_SUM power spectrum cast in the same units to give a reference of where shot noise lies.
Note: the excess noise we currently see is also present at 25W. It is almost identical to the 40W noise up to 200Hz. However, the notch structure between 200Hz and 700Hz is different at different power levels - no idea why.
Plot 2 shows the MICH coherence with DARM at 25W - the MICH-correction is not fine-tuned for that power level, but it is not the dominant contribution.
Guardian changes:
ISS_ON: based on IMC-PWR_IN_OUT16, set 25W or 40W offset.
# crude way to make it work at 25W and 40W (no intermediate!)
if ezca['IMC-PWR_IN_OUT16'] > 30:
ezca['PSL-ISS_SECONDLOOP_REF_SIGNAL_ANA']= -0.9326934814453125 # 40W
else:
ezca['PSL-ISS_SECONDLOOP_REF_SIGNAL_ANA']= -0.588 # 25W
LOWNOISE_ASC: The state used to only run >35W. Changed it to always run, except for the 40W compensation filters on CHARD_Y and DHARD_Y (FM6).
Couple of things that would be good to check:
Jenne, Sheila, Stefan
We used two independent methods to verify that the beam spot positions do not move during the power increase:
Jenne and Sheila put dither lines on all optics. While they have not calibrated the output, the result is that during the power increase they did not observe any motion of the beam, but during the soft offset adjustment just afterwards they did see the spots move.
I used Kiwamu's cameras to make time lapse movies of the power-up (the first two gifs). No spot motion is observed. I also atteched two movies (gif 3 and 4) of the motion during the soft offset adjustment. The spots can be seen wiggling.
FInally, I attached a Striptool chart of the beam positions during power-up. The power increase starts at -30 minutes, and finishes at -22minutes. Then the soft loops start moving until about -16 minutes. At -12 minutes Jenne took the soft offsets out again.
How to make gif movies
Attached are two scripts:
snapper.py grabs a snap shot from each of the 4 test mass cameras every 10 seconds.
makemovie converts those images into a gif movie.
(prefix and run number are hard-coded.)
Nutsinee, Kiwamu,
WP5990
We have (re-) set up the polarization monitors on the HWS table by HAM4. We have confirmed that they are functional. For those who are interested in the polarization data, here are the channels to look at:
In theory, they should be in unit of watts as measured at the HWS table.
[Installation notes]
This time, we have newly installed a short pass optic (DMSP950L from Thorlabs) to pick off the main interferometer beam without getting too much contamination from either the SLED light (790 nm) or the ALS beam (532 nm). The short pass mirror was inserted between the bottom periscope mirror and the first iris (D1400252-v1). Looking at the green light at the table from the end stations, we learned that the beam size is already pretty small and (visually) small enough for the beams to fit into the PDA50Bs without a lens. So we decided to go without lenses as opposed to the previous setup (24046).
The short pass mirror reflects the interferometer beam toward the left on D1400252. We placed a PBS (CM1-PBS25-1064-HP) on the left side of the short pass and placed the PDA50Bs. The power reflectivity of the newly installedshort pass mirror was measured to be 5% +/-3% for 532 nm. The absolute power (assuming the Nova hand held power meter is accurate) of the reflected green light was measured to be 1 uW.
One thing we leaned today was that the green light is not so trustable to get the optimum alignment. We first aligned the optics with the green light and then noticed that the infrared beams were almost falling off of the PDA80Bs. So we then closed the shutters and aligned them with the actual infrared beam.
The manual gain settings are:
The digital gains were also changed accordingly so that the calibration of these channels should be accurate.
This is a first look at the polarization data with the new setup. Some analysis with the previous setting was reported by Aidan at 25442 back in this February with a focus on noise behaviors. This time, since we are looking for a cause of the degradation in the power recycling gain, we focused on the time series rather than the spectra.
We saw two behavior in the polarization data when PSL was ~ 40 W.
Based on the fact that the amount of S-pol decreases as a function of time (which should increase the power recycling gain at the same time, naively speaking), I am inclining to say that the variation in the polarization is not a cause for the smaller power recycling gain.
[An observation from last night, July 13th]
I have used a lock stretch from last evening starting at ~ 2016-07-13 1:00 UTC for 2-ish hours. The attached two plots show the measured polarization in time series.
At the beginning of the lock stretch, the input power was increased step by step up to 40-ish W. The power recycling gain hit 35 right after completing the power-up operation and then settled to a lower value of 29 or so. The power in P-pol was about a factor of 8 larger than that for the S-pol. Note that this is opposite to what Livingston observed (G1501374-v1) where the S-pol was bigger than the P-pol. Back-propagating the measured power to those at BS's AR surface (the ones propagating from ITMX to BS), we estimated the power ratio to be Pp/Ps ~ 2500. This separation ratio is better than what has been measured at Livingston (G1501374-v1) by a factor of roughly 13.
[Another observation from Jan 31st for comparison]
I also looked at a similar data set from Jan 31st of this year (25442) to see if the polarization in the past behaved in the same way or not. This data was with a 20 W PSL without the HPO activated. The behavior looked similar to what we have observed last night -- a slow decay in the S-pol and P-pol was larger than the S-pol by a factor of 6-ish. See the attached below.
Matt later pointed out that there is a possibility that my measurement set up could be unintentionally rotated with respect to interferometer's polarization plane. In this case, depending on the rotation angle, the S-pol can appear to decrease even though the actual S-pol in the interferometer increases. I did a back of envelop calculation and confirmed that the measurement setup needs a rotation of about 20 deg to get such confusion [ angle = atan(sqrt(1/8) )]. I don't think we have such a big rotation in our setup. So it seems that the S-pol really decreases at the beginning of the lock stretch.
Here are some photos of our set up.
J. Kissel, S. Dwyer, S. Ballmer We continue to have trouble with the FSS oscillating after a lock loss, in that it'll often either take several minutes to relax, or it requires manual intervention such as briefly reducing the common gain of the FSS loop. As such, Sheila took a look at the IMC PDH loop to look for problems and instabilities there. I looked over her shoulder at her results, and saw some areas for improvement in the loop design. The current loop design has an UGF at 66 [kHz], with a phase margin of 68 [deg]. However the gain margin around ~200 [kHz] is pretty dismal because of what looks to be some icky features in the physical plant. These features have been shown to be directly influenced by the FSS common gain (see second attachment in LHO aLOG 28183). I figure, given that we've got oodles of phase margin, what harm could be done by just adding a simple 200 [kHz] pole in loop, and reducing the gain by ~2 [dB]? As such I took Sheila's data, which lives here /opt/rtcds/userapps/release/isc/common/scripts/netgpib/netgpibdata/TFAG4395A_12-07-2016_163422.txt (also attached) and added these modifications offline as a design study. In the attached plots, I compare the as-measured IMC PDH Open Loop Gain, G, Loop Suppression, (1/1+G), and the Closed Loop Gain, (G/1+G), against one modified as described above (blue is as measured, and green is the modified design study). The results are encouraging: a still-substantial UGF of 47 [kHz], and a very-healthy phase margin of 58 [deg]. However, as can bee seen in the loop suppression and the closed loop gain, there is far less gain-peaking and/or a much great gain margin and we would no longer have to worry about the icky features in the plant that are so sensitive to the FSS common gain. Where to stick such an analog filter? It's of course dubious to claim that the MEDM screen for such a system is representative of the analog electronics, but assuming it is, one can see that there is the possibility of a switchable daughter board in the FAST path that gets shipped off to the PSL AOM for the FSS. Because it's switchable, we can toss whatever simple filter in there that we like, and then compare and contrast the performance for ~1 week to see if it improves the stability problems we've been having. What impact would this have on the full IFO's CARM loop? I'll remind you of Evan's loop analysis of the whole frequency stabilization spaghetti monster in LHO aLOG 22188. There he suggests that the CARM UGF is around 17 kHz, so as long as the Closed Loop Gain around there is the same, then this change in the IMC PDH loop should have little impact [[I just made this sentence up based on just a few words from Sheila who asked me to look at the CLG. I'm not confident of its truth. Experts should chime in here]]. Indeed the third .pdf attachment shows that G/(1+G) of the IMC PDH loop, regardless of modification remains unity out to 100 [kHz].
How does this compare with the Pomona box from anno domini?
Description of the notch in pamona box 5141 (this was in the loop for a few years, but was removed serveral months ago, I think before O1)
Thanks for finding the aLOG entry Shiela! @Daniel -- though she doesn't say it explicitly, the aLOG shows that the Pomona Box notch was centered about ~700 kHz. As shown by my OLGTF model, if we add this ~200 kHz pole, then not only will any features at 200 kHz be suppress significantly, but whatever might happen at 700 kHz is even further suppressed. In otherwords this pole just shapes the high-frequency, super-UGF portion of the OLG to better handle *any* non-sense, instead of the focused bandaid fixes that any notch would provide.
