Over the last week, we've made a few tweaks to the SUS DriftMon such that it can be a quick tool to use when checking for drifting or misaligned suspensions. I've linked a smaller, more user friendly version of the monitor to the sitemap which can be tucked in a corner if useful. If channels are yellow or red and further investigation is needed, pop open the larger screen via the button in the lower right corner. From the larger screen you can also update the alarm levels to capture latest-and-greatest alignment. I have updated the monitor to a full lock time from this last weekend (2/09 14:10 UTC, 1107526216 GPS). I have adjusted the alarm thresholds of the SUS channels such that they tell you: YELLOW = you are close to the previously saved alignment, so likely just need some minor alignment tweaks RED = you are too far away from the previously saved alignment. If values are RED, and you are starting an initial alignment, it might mean: - The GUARDIAN for the SUS is in a misaligned state - WFS pointing offsets or FM integrators have been left on and need resetting - Possible temperature change in the VEA Note, RM1,2 and OM1,2,3 thresholds are pretty wide so I wouldn't expect them to go into alarm. These suspensions are not used to point beams into the IFO but instead direct beams onto WFS/PDs so we are more forgiving of their pointing. The OM chain might see more commissioning so we will tweak these alarm levels as needed.
The following maintenance tasks have been approved by Daniel for tomorrow:
* - task requires DAQ restart
We have had several reports of user accounts whose applets on the top right menu bar of their desktops have disappeared. We don't know why they disappear, but we know how to bring them back.
Attached is an image of what the top right should look like. If you are missing this, follow this procedure
If the applet icon is not in the correct position, move it by positioning your mouse on the icon and pressing 'ALT' + right-hand mouse button
no restarts reported. Conlog reports not available.
Items for Monday by Subsystem
SEI: Hugh/Jim reporting: Test Blend Filter changes, Feed Forward Filters ready to go,
SUS: no report
CDS: no report
3IFO: Richard reporting: Working on Baffle PDs in LVEA
facilities: Tumbleweed clean up until 10am inquired about for the week (Daniel mentioned tumbleweeding didn't affect too much)
PSL/Pcal: Rick reporting: EY visit for Pcal, ITM camera image work (work permit being made)
TCS: 3IFO inventory work
Items for Maintenance Tuesday (tomorrow)
Sheila, Alexa, Evan
We have transitoned CARM from digital normalized REFLAIR9I to analog REFLAIR9I, with a 4 kHz bandwidth and 50 degrees of phase. An OLTF is attached [the last data point is spurious, so ignore it]. This lock started at about 2015-02-09 12:24:00 UTC. We are leaving the IFO locked.
There is plenty of phase to push the bandwidth higher, but we have encountered large offsets induced by switching on the common-mode and summing-node boards.
We can also improve the low-frequency fluctuations of the CARM error signal by introducing an integrator somewhere; we need more dc gain.
Analog REFLAIR9I is plugged into input B2 on the summing-node board (SNB), with polarity "off". The output of B goes into input #2 on the common-mode board (CMB), with positive polarity. Digital normalized REFLAIR9I is plugged into input A1 on the SNB, with polarity "on". The output of A goes to input #1 on the CMB. [See LHO#16489 for a review.]
According to our reckoning, the shape of the digital CARM loop at the start of the transition is roughly 1/f above a few hertz. At a few hertz and below, it has a number of boosts and integrators which make it tricky to engineer a stable crossover with the analog signal.
Transition procedure is as follows, starting right after the guardian has brought the interferometer into resonance.
Also, the use of DHARD WFS (pitch and yaw) has removed the need for touching up the ETMs. However, since the AS36Q WFS feedback to the BS has not worked for the past couple of days, the BS had to be touched up by hand every so often.
In fact this lock lasted about 2.5 hours.
The lock broke due to a ~ 5kHz oscillation in the CARM loop (first plot). The second plots shows several locking attempts from last night. The drop in the sideband power observed during the first long lock last Friday , correlated with the increase of the carrier build-up during acuqisition, is not present anymore now that the locking sequence is much faster, so it might have been some thermal-induced effect. The third plot shows the trend of the power recycling sideband and carrier power, whose fluctuations are well correlated with angular PIT motion of the BS (ASC BS loops not yet closed, as Evan was saying).
Here are some numbers for arm buildup on resonance, recycling gain and stored arm power for last night's lock:
-IMC input power was 2.81W. Given modulation depths of Γ9 = 0.219(12) and Γ45 = 0.277(16), from alog 15674, the power in the sidebands is (Γ92+Γ452)/2=6%, there was 2.64W carrier power into IMC. 88% of this power is transmitted through the PSL-IMC-Faraday chain to PRM as measured in alog 13495.
-Arm buildup (X-arm) was 1200 x single arm power (1210 at the beginning of the lock). LSC-TR_X_QPD_B_SUM_OUTPUT was an average of 1035(10) cts during the lock stretch. This QPD is already roughly calibrated to arm buildup, but can be corrected for new input power levels as per Evan's alog 16450, so [arm buildup]=TR_X_QPD_B_SUM_OUTPUT*(10.95/2.82)*(3/10).
-Recycling gain was 36 W/W. [Recycling gain]=[arm buildup]/[PRM transmissivity], assuming PRM transmissisivty of 2.97% from galaxy page.
-X-arm cavity gain is 276 W/W. G_arm=( ti / (1-ri*re) ) ^2. Transmissivities Ti=1.39% and Te=3.6ppm according to galaxy webpage. re=sqrt(1-Te-Le) where Le is the x-arm loss is assumed to be 120(30)ppm based on alogs 16082, 15937, 15919.
-Power stored in the X-arm was 11.5kW. P_arm=[carrier power into PRC]*[recycling gain]*[0.5 (beamsplitter)]*[arm cavity gain]=2.64*0.88*36*0.5*276.
I made a typo in the equation for recycling gain, which should read: [Recycling gain]=[arm buildup]*[PRM transmissivity]
Evan, Alexa, Lisa, Ryan, Sheila
Today we were able to lock about 7 more times todat, for at most a half hour.
We have many examples of locklosses from today. We have added lock loss states to the guardians, so we should be able to get a list of these off the Detchar summary pages or the command line utility.
The inability to zero AS_I tends to be an inidcation of unequal RF sidebands, either in amplitude or shape. This is generally caused by the Schnupp asymmetry togther with a differential short Michelson effect such as a differential thermal lens or to a lesser degree ITM alignment and dark fringe offsets.
Now we have a faster DHARD yaw loop during CARM offset reduction, analogous to the fast DHARD pitch loop that Elli, Ryan and I commissioned last week (LHO#16544, LHO#16520). Injecting a step response at the error point shows a loop time constant of a few seconds.
With the loop open, I injected ASC-DHARD_Y_EXC with bandlimited noise from 0 to 3 Hz and measured the transfer funcion ASC-DHARD_Y_EXC → ASC-DHARD_Y_IN1. Since we have no yaw oplev damping on the ETMs, the optomechanical plant has two moderately high-Q resonances, which I estimate to be at 0.6 Hz with a Q of 18, and at 1.36 Hz with a Q of 45.
The attachment shows the plant measurement, along with the analytical system used for the plant inversion. Here I've intentionally lowed the second Q from 45 to 20, to avoid excessive ringing in the filter step response.
Just to be clear, these are not truly DHARD loops, since we're not actuating on the ITMs. Really it's just the differential angular motion of the ETMs.
Both DHARD loops are meant to be engaged with FM3, FM4 (giving a 1/f shape overall), FM8 (plant inversion plus high-frequency rolloff), and F10 (30 Hz elliptic low-pass). For pitch, gain is 16 ct/ct, and for yaw, gain is 200 ct/ct. In contrast to what I said in LHO#16520, nothing should be engaged in the ETM L2 lock filter modules.
Additionally, these loops currently require us to disable the M0 and L1 pitch/yaw lock filter banks on the ETM suspensions. This prevents the DHARD control signals from being offloaded to the upper stages.
model restarts logged for Sat 07/Feb/2015
2015_02_07 10:29 h1fw1
Unexpected restart. First fw restart since 03Feb (4.8days)
During the early steps of the CARM offset reduction last night it was observed that the ALS DIFF bandwidth was a little low, causing lock losses around the arm power where the transition to the tranmsission QPD sums takes place. To continue locking work the gain was doubled, but it was noted that this should not really change. Today, the ALS diff loop was re-measured, and found to be close to the expected value (under nominal gain settings), so its not clear what happened. At the same time, it was noticed that the length control was ringing at 1.56 Hz, which is sometimes associated with mismatched L1/L3 crossover. A quick measurement of this did not reveal any problem, and somewhat incidentially it was discovered that the alignment of the reaction chain has a significant effect on the length control at this frequency (the reaction chain had previously been adjusted for a different test), potentially due to angular cross-coupling. This should be investigated further.
Attached shows the oplev spectra, showing the 1.56Hz oscillation. I have also attached a screen shot showing the green x transmission (blue line), which is clearly oscillation to begin with, and then we re-align the reaction mass and this oscillation goes away, but we see a drift in alignment of the test mass.
A core switch in the OSB hung up over night. A reboot of the offending switch returned service to wired network, wireless, and phones at approximately 12:35PM PT. After the reboot, the firmware was upgraded to the latest release of the same major version due to multiple candidate causes of the issue we are seeing having been fixed.
The HWS on ITMX was running during last night's 1 hour lock. It saw a lens of ~6 micro-diopters (double-passed) form while the IFO was locked. The transient data is in the attached plot.
HWSY is not currently operational.
At the moment, I can't reliably estimate the absorption coefficient, but the absorbed power is about 1.06 mW per micro-diopter (double-passed), so roughly 6mW of power was absorbed.
If I go with 2W requested from the PSL rotation stage and do the same calculation we did at LLO:
2W (input power) * 30 (recycling gain) * 0.5 (beam splitter) * 286 (arm cavity gain) = 8.6kW stored arm power,
which yields
I would definitely take this number with a healthy grain of salt ... I'd still like to run some diagnostics on the ITMX HWS following yesterday's code update.
(Also, the data in the attached plot was rescaled in dataviewer, by 0.00326, to what is currently displayed to account for the fact that the HWS magnification was set to 1x at the time of this measurement, rather than 17.5x. The spherical power scales as 1/M^2 = 1/17.5^2 = 0.00326).
I've added this data to the TCS actuator couplings document on the DCC.
I've calculated the stored arm power from last night's lock as 11.5kW (As calculated in post 16579).
Using this number instead of 8.6kW approximated from livingston's numbers, this brings the estimate of absorption in the ITMX coating to 520 parts per billion.
This came up a couple of times this week, and Aidan and I just figured out how to do it, so for those that don't already know:
You can scale data in plotted in dataviewer by going to menu: Data->Transformations->Geometric transforms...
Transformations are cumulative. In other words, if I select "Scale = 10.0" and hit "Accept" twice, the data is scaled by 100.
Ryan, Lisa, Evan
We have been locked for more than 1 hour with CARM controlled by digital REFL9I (at 0 pm offset) and DARM controlled by ASAIR 45Q. The power buildup is 1100 times the single-arm buildup, giving an interferometer recycling gain of 33 W/W. The REFL_A_LF power is 1.35 ct, compared to 21 ct with the arms held off resonance. This means the interferometer visibility is about 94%.
The new element today was a higher-bandwidth DHARD pitch WFS loop. The loop time constant is a few seconds or so, and is fast enough to suppress the appearance of the microseism in ASAIR 45Q. Next steps are probably to close the analogous yaw loop. Ryan had to adjust ETM differential yaw by hand several times to keep the AS beam reasonably round. Also, Ryan had to add a DC-coupled oplev servo to ETMX L1 pitch in order to keep the optic from drifting.
Details will be posted later.
These are the plots with the transition to REFL 9I, and a trend of the 1 hour long lock (starting around Feb 7, 12.11 UTC). In the first plot, the power build up increase around 400 sec is due to the improvement of differential YAW alignment that Ryan did by hand. The lock loss happened right after a DARM loop measurement. The high wind of the afternoon was totally gone by the time we came back to the site after dinner.
Congratulations! and thanks for staying up all night once again.
Welcome news. Great job. Congratulations to everyone who has helped bring this about.
Awesome! Very pleased to see this result. Nice work everyone!
Congratulations from Delhi! Nice to see the stability of lock at this early stage. The entire team deserves credit for undaunted persistence through all the tricky issues. Y'all rock.
In my previous trends I plotted the wrong POP18 signal (before demodulation), here is the correct signal representative of the sideband power. Once the arm cavity power increases from ~ 500 to ~1000 single arm power, the sideband power decreases by ~20% in about 10 min.