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.
15:20 UTC Chris S. starting beam tube tunnel sealing (first 150 yards of X arm) 16:19 UTC Elli, Cao to Y arm TCS table to check beam 16:39 UTC Elli and Cao back 17:21 UTC Ed and I done transitioning LVEA to laser safe, Bubba and John starting crane shimming 17:45 UTC Richard to H1 PSL enclosure to check door lock 17:50 UTC Kiwamu, Elli and Cao to LVEA to turn on Y arm CO2 laser 17:51 UTC Richard back 17:57 UTC Kiwamu, Elli and Cao back 18:07 UTC Karen and Christina opening OSB receiving door to bring in 51 lb package 19:01 UTC John and Bubba done for the day 19:26 UTC Dave rebooting hardware injection machine (WP 5740) 19:53 UTC Dave done 21:20 UTC ASCIMC model restarted 21:22 UTC LSC model restarted 21:24 UTC DAQ restart 21:32 UTC Kiwamu transitioning to laser hazard 21:39 UTC Kiwamu done transitioning to laser hazard, Elli and Cao to ISCT6 22:03 UTC Vinny and Brynley to end Y, opening middle rollup door to move temporary magnetometer - beam tube tunnel sealing (Chris S.) - crane work (John, Bubba) - TCS work (Elli, Cao) - ASCIMC and LSC model changes (Sheila) - PEM work (Vinny and Brynley) - tconvert fix (Dave)
Laser Status: SysStat is good Front End power is 32.51 W (should be around 30 W) Frontend Watch is GREEN HPO Watch is RED PMC: It has been locked for 18.0 days 6.0 hours and 18.0 minutes (should be days/weeks) Reflected power is 3.157 W and PowerSum = 25.62 W. FSS: It has been locked for 0.0 days 6.0 hours and 3.0 minutes (should be days/weeks) TPD[V] = 1.476 V (min 0.9V) ISS: The diffracted power is around 7.85% (should be 5-9%) Last saturation event was 0.0 days 6.0 hours and 3.0 minutes ago (should be days/weeks)
Evan, Sheila
We made some changes to the LSC model and medm screen as described in ECR 1205. The main goals were to split the SRCL FF filter into two parrallel banks, so that one can be used for the low frequency feedforward that needs to be tuned as the darm offset is changed and the other can be used for the high frequency part that we don't expect to change much as we change the DARM offset and power up. I also added a power recycling gain monitor, based on POP A LF divided by IM4 trans sum. For this we had to add an IPC send to the IMCASC model, an a receive to the LSC top model, in addition to the modifications to the LSC common model. Both the models and medm screens are checked into svn. Evan also added a PRCL FF path to the FF medm screen, but it is not in the model.
I calibrated the PR gain by looking at a recent lock stretch, taking the average of the normalized arm transmissions and multiplying them by the PRM transmission (2.7%) to get the recycling gain, and then finding the factor needed for the new monitor based on that.
(Keita Daniel)
We mounted the 9 MHz RF AM Stabilization chassis in the CER in preparation of tomorrows installation in the PSL enclosure. The remote control is working fine.
Comment 1: The little back panel PCB became loose during shipping and needed to be reseated. It is important to make sure it is correctly centered, since the connectors are not keyed (the power supply will blow, if it is shifted by one).
Comment 2: In a Frankenstein experiment someone disassembled the high power sensor for the RF power meter and then equipped it with a different sensor head. Please don't. The sensor head and power attenuator constitutes a single sensor and should never be taken apart.
A while ago I worked on feed forward from BSC St1 sensors to St2 in Z. I've installed this and it has been running on all BSCs for a while, but I have taken my time in logging it. Attached spectra show the improvement, where dashed is on (ground STS and St2 gs-13s) and solid is off. Almost an order of magnitude improvement over 10 to 25 hz. It does do slightly worse at 4-5 hz, because of gain peaking, but we are mostly into gs13 noise at that point anyway. I've worked some on other DOFs, but Z was the easiest to do with the worst performance. In X&Y the existing controls already mostly keep us in the GS13 noise, so the room for improvement is smaller.
FRS 4412 A new environment variable, TCLEAPSDIR, has been created with the value /ligo/data/tcleaps. This is to get all versions of tconvert to use the same leap seconds file instead of having a separate file for each operating system. This is the first step in solving the issue described in the FRS 4412.
The CO2Y laser RTD sensor tripped and shut off the laser on 19 Feb 17:52 UTC. We restarted the laser on 22 Feb 18:00 UTC. The RTD sensor is a temperature sensor mounted on the CO2 laser viewport. It's pourpose its to shut off the CO2 laser if the laser is heating this vieport. However I don't think this is what happened here, because now we are using the CO2Y laser to heat the ITMY and the RTD sensor has not tripped.
BSFM and QUAD AUX model revert (Tuesday) (Jeff K.) Crane work (potential all week) (John, Bubba) X arm ion pump is still down from cable short Retrieve spare PMC from H1 laser room (Tuesday) (Rick) Short internet outage (Tuesday 8:00 am) (Ryan) Dust monitor work at one of the end stations (Tuesday) (Jeff B.)
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.
Cao, Elli
To measure the SRC gouy phase, we need to move the BS and PR2 optics in yaw and know the angle we move them to at least 5% (but ideally more like 2%). So today we checked the calibration of these optics' alignment sliders using the ETMY baffle PDs. We have used the method which was previously used to calibrate the BS optic align sliders (alog 14321), although we have taken extra care to loacte the center of the baffle PDs, as we are particularly interested in understanding the accuracy of this measurement. Just to be clear, we are not making any changes to the alignment slider gains, we are simply measuring how good the current ones are.
Method:
The BS was moved in pitch and yaw to direct the PSL beam onto each of the ETMY baffle PDs (PD1 and PD4). PRM, SRM, ITMs, ETMs and TMSs were misaligned to prevent flashes from other optics from corrupting the baffle PD signal. Once the PSL beam was directed onto a baffle PD, we moved the BS around and plotted BS location vs intensity. We fit gaussian profile to this plot to pinpoint the BS slider values for when the beam is centered on each of the baffle PDs. (Attached are the plots of slider value vs PD power and the fited gaussian, for the BS).
This procedure was repeated using the PR2 to direct the beam onto each baffle PD.
Results:
BS | ||
P "urad" | Y "urad" | |
ETMY PD1 | 150.7+/-0.1 | -294.1+/-0.1 |
ETMY PD4 | 186.3+/-0.1 | -329.4+/-0.1 |
Difference in optic align values when moving from PD1 to PD4 | 35.6+/-0.2 | 35.3+/-0.2 |
Multipied by 2 for angle beam moves to go from PD1 to PD2 | 71.2+/-0.5% | 70.6+/-0.5% |
We can check the calibration of these sliders by comparing to the angle the beam moves through to move from PD1 to PD4, as calulated from the geometry of the interferometer. Accordong to Jeff and Gerado (alog 14321, D1200296), the baffle PD locations are 11.329 [inches] = 0.288 [m] apart in vertical, and 11.313 [inches] = 0.287 [m] apart in horizontal. With a 3994.5m long arm (LHO aLOG 11611), and 4.986 [m] for the distance between the HR surface of the BS and the back of the ITMY CP, through the thin CP, through the ITMY to the HR surface of ITM, respectively (D0901920), that's a lever arm of 3999.5 [m]. Hence, a displacement of
BS P 0.288 [m] / 3999.5 [m] = 72.01 [urad]
BS Y 0.287 [m] / 3999.5 [m] = 71.76 [urad]
The alignment offset slider gains can therefore be corrected by
BS P 72.01 / 71.2 = 1.011 [urad/"urad"]
BS Y 71.76 /70.6 = 1.016 [urad/"urad"]
or
BS P 0.989["urad"/urad]
BS Y 0.984 ["urad"/urad]
Which means the BS calibration is pretty bloody good. Go team!
Checking the calibration of the PR2 alignment sliders can be done similarly, provided we take into account the extra distance from PR2 to PR3 to BS, and the ROC of the PR3. This looks like a job for tomorrow.
PR2 | ||
P | Y | |
ETMY PD1 | 1699+/-1 | 4475+/-1 |
ETMY PD4 | 1957+/-1 | 4180+/-1 |
Difference in optic align values when moving from PD1 to PD4 | 258+/-2 | 295+/-2 |
We broke the lock this morning to do this measurement. We have returned all optics to where they were and are leaving the interferometer in the down state (I had a shot at relocking but I've been away too long it appears :( ).
Den, Kiwamu, Evan
Tonight we again made it to low noise, although the locking procedure is still not robust enough. In the end, it seems that the sensitivity degredation is not due to a new mystery noise, but rather is a consequence of a shift in the interferometer alignment and some left-over temporary equipment.
List of changes/observations for locking is as follows:
Once we reached the low-noise state, we again saw the excess noise that has been bothering us for the past few days. We were able to partially mitigate this as follows:
The sensitivity is now 70–76 Mpc.
Finally, we looked for high-frequency frequency noise downconverting into DARM. We didn't see anything, but here is what we did:
We also made some tweaks to the ALS locking:
Attached are transfer functions of IMC jitter (sensed by the IMC WFS) into DARM, compared against the previous TFs measured in September. One can see that the pitch coupling is higher by more than a factor of 3.
Den, Evan, Sheila, Hang
We've spent some time on ASC today. First of all we added yesterday's changes to the DRMI ASC (25630) to the guardian, but used the new AS36 A phasing from early this morning. This seems to work fine.
We also measured the sensing matrix for the INP1, PR3, and CHARD in the refl WFS. For pitch, in counts/counts
CHARD | IM4 | PR3 | |
9A | 1.9 | -5.9 | 1 |
9B | 2.3 | 4.3 | 4.7 |
45A | 2 | -4.9 | -2 |
45B | 2.4 | 4.0 | -2.3 |
excitation amp | 3e3 | 100 | 200 |
demod phase | 0 | 90 | 0 |
Den set this up using the locking oscillator, the excitation amplitude and demod phases used are for future reference. For yaw:
CHARD | IM4 | PR3 | |
9A | -2.1 | 7.8 | -3.4 |
9B | -3.3 | -5.1 | -7.8 |
45A | -2.1 | 8.3 | -0.4 |
45B | -2 | -4.6 | 4.06 |
excitation amp | 3e3 | 100 | 200 |
demod phase | 0 | 90 | 0 |
Since Den noticed that the values of the sensing matrix we got for REFL45A were fluctuating (and small compared to the others), we did not use it.
The POP offsets have changed, and right now we are using small offsets in the soft loop error points.
To summarize the last few days, we had some kind of alignment problem perhaps because of a temperature swing in the lvea on tuesday. We have fixed a few things that have been longstanding oddities in our ASC system:
This seems like great progress, although we clearly have more work to do increasing gains, and getting rid of some cross couplings between loops. Most of the new settings have been accepted into SDF, and we think all of them are in guardian, which we are about to test.
In the past 2 weeks, the crew cleaned 286 meters of Y beam tube ending at HSW-01-058. The support tubes in that same section were vacuumed and capped also.