I have subtracted  SRCL coupling from DARM, and found that residual noise has the shape of 1/f^4-5 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.

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:

>> 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).

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:

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.

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:

• We found that engaging true differential hard loops (instead of differential ETM loops) during the CARM reduction sequence causes the sideband powers to drop too much. So ITM feedback should only be turned on once resonance is achieved.
• We are still coming into resonance with middling recycling gain, sometimes too low to engage the Refl 45 MHz → PR3 loop. The procedure that works most of the time is to gently engage the soft yaw loops, which brings the recycling gain above 36 W/W. Then the soft pitch loops are engaged with error point offsets (0.1 ct for differential and −0.1 ct for common). The offsets in the QPD pitch/yaw filters have not been changed.
• With good recycling gain (>38 W/W) at 2 W, we adjusted the ALS Y camera offset setpoints. The ALS X setpoints didn't seem to need adjustment.
• Kiwamu found that the TMSX yaw OSEM readbacks had moved several days ago, coincident with the amplifier swap. We don't necessarily believe that this represents a real motion of the TMS.
• In the guardian we now engage 5 Hz low-pass filters in the beamsplitter angular loops, and a slight boost in the Michelson length loop. This prevents loop instability during power-up.
• Several times we saw the return of the 0.4 Hz angular instability when powering up with mediocre recycling gain.

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 dsub breakout board for OMC measurements was removed. This seems to have fixed the majority of the broadband excess noise from 20 to 100 Hz.
• We retuned the test-mass angle-to-length decoupling. At first we tried using the script, but it didn't do a good job. So we did it by hand. This fixed the excess noise below 20 Hz. Mistuned A2L is consistent with the interferometer being in a different alignment state.
• The SRCL feedforward had to be retuned. Again this is consistent with the interferometer being in a different alignment state. For now, we just retuned the gain. Den suggests using a flat FF filter (which will take care of the radiation pressure coupling) and not worrying about the junk coupling above 80 Hz.
• The jitter coupling into DARM is worse, particularly around 290 Hz. Again this is consistent with the interferometer being in a different alignment state. The 290 Hz peak is also visible in the pitch/yaw IM4 transmission signals, but it seems to have been there last week as well. So it seems the jitter exiting the IMC has not changed.

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 used an SR785 to drive a ~20 mVpk sine wave into the CARM error point. We swept the frequency from 30 kHz to 100 kHz while watching the DCPD sum. We didn't see anything.
• Then we used the 4396B to drive a ~20 mVpk sine wave from 100 kHz to 10 MHz. We didn't see anything.

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

Den set this up using the locking oscillator, the excitation amplitude and demod phases used are for future reference.  For yaw:

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:

• We now have phases for AS36 and REFL 45 that seem sensible (they mostly within a few degrees for all the quadrants on one head, except for SA36B with has a 20 degree spread.)
• We are now using normal matrices for all the WFS, no more random zeroed quadrants. 
• We are no longer switching our AS36 input matrix around as we power up. 

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.