It's been some time coming but Jim finally decided to give in and say goodbye to the #1 BSC-ISI for 3IFO.
The monitor point reads 13V, and the ADC reads -20000cts, even with the input terminated. The busted channel (CH4 is used for the green y-arm transmitted power, and was temporarily used for ITMY dither alignment by hooking it up to POB18_Q.
These are current amplifiers with a -5V dc bias and 1k series resistor. They are only intended for unamplified photodiodes! Grounding them produces a 5mA current which can rail the output (depending on the selected gain). D1200543.
J. Kissel, J. Bartlett Unclear if there was any smoking gun, but H1 ISI BS, H1 ISI ITMX, and H1 ISI ITMY all tripped at 10:32a PT (1078165983). PRCL team was in LVEA near IOT2, Andres was working near Test Stand, nobody doing any heavy lifting, no earthquakes. ISI Configs: Chamber Isolation Filters Blend Filters First Trigger ITMX Level 3 TCrappy ST1 T240 ITMY Level 3 TCrappy ST1 Act BS Level 3 T40mHz_N0.44 ST1 Act
Yuta, Stefan, Kiwamu
This morning, we newly started using the BS M1 longitudinal actuator to make the PRMI lock more solid. This works well.
BS M1 stage feedback:
Our next target is to get the PRC length measurement done. In order to do that, we needed the PRMI locked for a sufficiently long time (more than 20 min). This morning, we found that the PRMI dropping the lock every 5-10 minutes. After some investgations, we found that the lock loss was due to the BS M2 actuator hitting the DAC range. There was a large motion in the Michelson over a time scale of 20 sec. So we decided to use the top mass of the BS to help the M2 stage actuator at the low frequencies.
The attached is the current-emperically-optmized top stage feedback. It seems helping the middle stage a lot at the low frequencies, resulting in a long PRMI stretch. As of now, it stayed locked for more than 30 minutes and is still locked. This feedback is implented in the guardian so that it automatically engages it when the PRMI becomes locked. We didn't measure the crossover frequency, though it should be around 0.1-ish Hz.
Limitter in PRM M2 stage:
We put a new feature in our lock acquisition sequence in which a limiter in PRM M2 stage limits the feedback when the interferometer is in the acquire state. It seemed that the most shaky optic was PRM during the lock acquisitoin. The limitter reduces the kick in PRM and hope this increases the chance to grab the PRMI fringe. We will see how this goes.
Schmitt trigger in guardian:
We implemented a Schmitt trigger in the LSC guardian so that now the unlocked and locked thresholds are different.
J. Kissel, J. Warner Jim had reported in the morning install meeting that H1 SUS ETMY had tripped at ~12:30a PT last night after a few bands of transfer functions. Turns out the reaction chain (R0) had tripped alone, because its damping loops were OFF. I've ensured the loops are installed, and turned them ON.
So as to not interfere with the purple *ahem* PRCL team, I've misaligned H1 SUS ETMX.
Aligned Misaligned [urad]
P 7.3 200
Y 82.9 400
While Stefan reported that ETMX HEPI 'seems to have moved' in 10570, I show that it has in fact not. The trend of the positions attached show rock steady position for the last three days. There were two periods of HEPI trip where it of course was not in position. These times are 4 March ~1320--1400 and 6 March 1600-1740pst. I checked the IPS to Cartesian matrix values and they are unchanged.
Yuta and I noticed that there was a funny glitch frequently (maybe once a minute or so) in the PRX signal as well as the IMC transmitted power. It turned out that this was due the ISS keeping trying to acquire the locked loop with no success. According to a 2 days trend (see the attached), the diffraction power dropped quite rapidly yesterday and eventually plunged into a so small value that the ISS can not lock itself any more. Because of that, the ISS had been down from 22 pm local yesterday. I increased the offset in the error signal (H1:PSL-ISS_REFSIGNAL) from -1.85 to -1.75. This brought the diffraction power back to the nominal of 10%. Now it seems running fine without a difficulties in locking it.
By the way, this was written by Kiwamu, not Stefan.
For the blue team:
Before I started the PRMI commissioning I switched off the WFS. I disabled the signals at the input side i.e. ALS-X_WFS_DOF_1(2)_P(Y)_INPUT.
The green light was locked on the 00 mode, although, as Keita wrote in his entry (alog 10571), the spot on the ISCT1 CCD monitor seemed a bit too low and shifted toward the right hand side on the monitor compared with the black circle on the monitor.
Because I wanted to maintain the same arm alignment, I manually offloaded the feedback to the OPTICALIGN biases of both ETMX and ITMX. Then I misalgiend ETMX by the guardian.
Of course the new biases after the offload were saved through the ASC IFO screen. One can go back to the same alignment by simply telling the guardian to align ITMX or ETMX.
ALS COMM was even more noisy tonight than last night, and now it is not stable at all. This could be because of the increased seismic noise, or some other reason.
The X arm guardian is working (there is no WFS control yet), I am leaving the arm locked with WFS on and no slow feedback to the ETM. It also seems like the COMM guardian is also working, but I'll need to test it sometime when the ALS COMM loop itself is working.
I started some excitations for Keita, screenshot attached.
written by Kiwamu I stopped the excitation at 6:10 AM local.
Seems like the green transmission is not on the same spot as last night, maybe the TMS moved.
We had some difficulty engaging the WFS because the whitening gains were all reset to 0dB and white/awhite were mismatched and Lock path for the ITM was off.
After these were fixed the WFS started working, today the transmission power doesn't go to 850 cts, it stays 750-800.
I'm leaving WFS on for the night, and when Sheila is done she'll start the excitation for the ITM and ETM.
[Keita Jeff Arnaud]
Several measurements were taken on ETMX for top mass length to test mass pitch decoupling as well as for the pum tf inversion (cf Keita's aLog), and are summarized in the attached plot.
Page 1 and 2 : Top mass to test mass TF compared with the "fiber" model, length to pitch (p1), pitch to pitch (p2)
Page 3 and 4 : Pum to test mass TF compared with the "fiber" model, pitch to pitch (p3), yaw to yaw (p4)
Points with an uncertainty lower than 10% have been removed from the transfer functions.The data for the length to pitch (2nd page) is a combination of a swept sine measurement, and a white noise measurement.
Measurements slightly differs from the model, especially for the top mass pitch to test mass pitch (p2), thas has its first pitch mode shifted down. It would be interesting to plot those measurements against the correction that is beeing made to the current model.
The data for the pum pitch to test mass pitch doesn't have any coherence below 0.6Hz, and those points have been deleted because of a low uncertainty, so it is currently hard to do a fit with the few points we have. I would like to try few more times tomorrow to do this TF again.
In the meanwhile, I will use Keita's happyVecfit function to do the top mass fitting, and calculate -L2P/P2P
Yuta, Kiwamu, Daniel, Sheila, Dave, Evan, Stefan After we had the PRMI drive properly balanced (alog 10559), we fine-tuned the 3f-locking again: - Added a 60Hz (triggered) notch in MICH to reduce the RMS drive to BS and PRM. - AC-coupled the PR2 drive at 2Hz - it was saturating at DC. - Reset the REFLAIR_B_RF27: two stages of whitening, 27dB of whitening gain, digital gain of 1. - With that the 3f lock by itself was fairly stable - lock duration was limited only by user impatience. Next we brought up the green arm - for some reason ETMX-HEPI seems to have moved - we had to re-align both TMS and ETMX suspensions. - After manually tweaking the green arm alignment the COMM_handoff worked fine. - We parked the about 12kHz avaiy from resonance and locked PRMI. - PRMI locking im this configuration seemed more difficult. Attached is a plot of the control outputs once locked - we were again frequently saturating the BS and PRM. - Ignoring all that we switched to 3f-locking, and brought the red on resonance - it stayed locked.... .... ... but we don't understand the red build-up. It's wasn't any higher than single shot.... something aint right quite yet, but I need a beer. EDIT (after the beer): The build-up actually makes perfect sense: The reflectivity sign flip of the ITMX due to arm resonance means the Michelson is exactly anti-resonant, redirecting all the light to the dark port. effectively no light gets back to the PRM. Hence the incident power on ITMX is equal to the (PRM misaligned) single shot power. We also had rockIFO playing the PRCL signal while we put the arm on resonance, and couldn’t hear any rumbling. To do next: measure length sensing matrix in PRMI and in state 3 (which we should lock on red using the 1f-signal).
The attached plot shows time traces for the combined 3f and x-arm cavity lock. The top left pad shows the frequency dialed into the COMM VCO. It is the calibrated green laser frequency in kHz. The red beam is resonant when the green frequency was near -37 kHz and was parked 10 kHz above. This is a 5 kHz offset for the red laser frequency. We verified that this is the direction away from the higher order transverse modes.
The bottom left plot shows the green transmitted power as measured in the corner station. The x-arm was locked to the green ALS laser most of the time.
The bottom right plot shows the POP_B demodulated signal for 2f. When high, it is an indication that the 1f-sideband is resonant in the PRMI. The lock was achieved with the 1f-signals and then switched over to the 3f-signals.
The top right plot shows the red transmitted power in the x-end station. With the green locked, it will typically dither around resonance, when the COMM PLL frequency is set to the red resonance. The first region of red arm cavity locking is with the PR mirror misaligned. During the 3f-lock the arm cavity was first parked away from resonance to facilitate locking, and then brought near resonance. The PRMI stayed locked using the 3f-signals during the entire transition! The transmitted power was about equal to the power when the PR mirror was misaligned. With the PRMI locked on sidebands and only one arm locked, there is a 180º phase shift for the carrier in the Michelson. Hence, all the carrier power is guided towards the AS port.
I've been updating the MEDM screens to be sure that all the BSC-ISIs currently used are consistent with eachothers.
Right now, BS, ITMX, ITMY & ETMX have:
- the Start, Tstart and Tcrappy blends installed respectively in blend banks 1, 2 and 3
- a working controller (lvl3 on ITMX & ITMY, lvl2 on BS & ETMX)
- tilt decoupling on ST1 for all them, except BS.
Putting on the controllers with Tcrappy blends on all DOFs for ST1 and ST2 provide a robust configuration with good performance on all these ISIs.
In other words, everything looks good into the seismic world!
There is of course some room for improvement. We're currently in an aggressive configuration, sensitive to varation of the input motion. Adding tilt decoupling on stage2 will help pushing the performance. I'll work on that as soon as I have access to a platform.
