We've been stably locked with a recycling gain of 38 at 23.3 Watts for almost 2 hours (I intentionally broke the lock).   There were some of the slow (20 second) oscillations that cause some of our locklosses durring ER7.  

When I first came in I had some trouble with locklosses durring ENGAGE_ASC.  One problem was just a typo, the other one seems to be when the gain is increased for the SRC2 loop.  I think this caused the increase in POP90 we were seeing last night, which went away.  This morning it kept increasing until the lockl dropped. I moved the transmon QPD offsets back to the pre-vent offsets, powered up to 18 Watts, turned off the ITM loops and adjusted the ITMY alingments slightly to get a decent recycling gain.    The green alignment in the arm was OK here, and the camera positions not off by more than 4 counts so I did not update the references. 

The offsets where we are stable with recycling gain of 38 and 23.3 Watts are:  

Before ER7 we noticed that we have a better signal for damping the ETMX roll mode in AS 45Q yaw than in pitch. Durring the vent we added a matrix to the ASC model to allow switching.  On Friday Nic found that the old settings for damping ETMX roll (using AS45Q PIT) were not working, so he found some settings that worked using DARM err alog 19561.  

Today I needed to damp ETMX roll again, so I tried using AS45 Yaw, this worked well, with a phase of -90 degrees relative to the settings we had for pitch (so we use bp 13.9, -60degrees, -30 degrees, -100dB and a gain of 60).  I also attempted to damp ITMX and ETMY using AS 45 Yaw (which has better SNR for these as well).    

While these settings seemed to work for each individual optic, when I turned all three on and left them on simultaneously for several minutes, they rang up all the modes.  

Reminder, the nominal settings for bounce and roll damping (with AS pit) can be found in alog18614.  

We've tracked down a few settings which became wrong durring our down time.  

BS OpLev yaw limit was set to 0, so we were not using yaw damping while trying to acquired DRMI (it has been working OK).

ITMY violin mode damping for mode6 had the wrong filters engaged.  This rang up the mode, meaning that we had to reduce the whitening gain for the DCPDs.  Now that the right filters are engaged the mode is coming down.  I went through and made sure that the handfull of violin mode damping settings that were not monitored are.  We use guardian to set the gains for these filterbanks, but not to choose the switch status.  

Sheila, Evan, Stefan,
With information for Sheila on Sun morning

We tried to operate the ASC system at full power (24W), using two different sets of QPD offsets (I'll call them pre-vent and post-vent, see burt files below).

With the pre-vent offsets we
 - The ASC system was stable at full input power
 - We had a recycling gain of about 36. (Based on transmitted power.)
 - These QPD offsets are not compatible with the current initial alignment (i.e. the Guardian will drop lock during ENGAGE_ASC - however a slow 2-min offset ramp from post-vent to pre-vent, with 20dB lower gains on the ITM loops worked)

With the post-vent offsets we
 - Get a recycling gain of 40. (Based on transmitted power.)
 - These QPD offsets are compatible with the current initial alignment. The ENGAGE_ASC step works fine.
 - Assuming the higher recycling gain is real (and not due to a difference in QPD clipping), we'd like to keep those QPD offsets because of the higher recycling gain.
 - However we get a 0.41Hz oscillation which starts at about 20W or 21W.


About this 0.41Hz oscillation:
 - It shows up in arm build-up's as 0.41Hz modulation (i.e. 1-f).
 - It is CSOFT PITCH, i.e. all 4 test mass optical levers show it exactly in phase.
 - The arm powers are exactly out-of-phase with the optical level pitch signals, i.e. when all optics point downward (highest OL value), the arm power is at a minimum. (see plot)
 - 

To deal with this mode, we switched the ITM ASC loops for PITCH to the common/differential basis (i.e. DSOFT is now DITM, and CSOFT is now CITM). At the time of this elog we were still designing a filter to stabilize the oscillation.



========================================================================================
Pre-vent QPD offsets (in /ligo/home/evan.hall/Public/Burt/ItmQPDsPre.snap burt file):
H1:ASC-X_TR_A_PIT_OFFSET 1 -2.900000000000000e-02
H1:ASC-X_TR_B_PIT_OFFSET 1 -1.580000000000000e-01
H1:ASC-X_TR_A_YAW_OFFSET 1 -7.000000000000000e-03
H1:ASC-X_TR_B_YAW_OFFSET 1 1.050000000000000e-01
H1:ASC-Y_TR_A_PIT_OFFSET 1 1.010000000000000e-01
H1:ASC-Y_TR_B_PIT_OFFSET 1 -5.600000000000000e-02
H1:ASC-Y_TR_A_YAW_OFFSET 1 -1.270000000000000e-01
H1:ASC-Y_TR_B_YAW_OFFSET 1 5.500000000000000e-02

Post-vent QPD offsets (in /ligo/home/evan.hall/Public/Burt/ItmQPDsPost.snap burt file):
H1:ASC-X_TR_A_PIT_OFFSET 1 -4.800000000000000e-02
H1:ASC-X_TR_B_PIT_OFFSET 1 -1.480000000000000e-01
H1:ASC-X_TR_A_YAW_OFFSET 1 -4.000000000000000e-03
H1:ASC-X_TR_B_YAW_OFFSET 1 7.800000000000000e-02
H1:ASC-Y_TR_A_PIT_OFFSET 1 -1.180000000000000e-01
H1:ASC-Y_TR_B_PIT_OFFSET 1 -3.690000000000000e-01
H1:ASC-Y_TR_A_YAW_OFFSET 1 -2.420000000000000e-01
H1:ASC-Y_TR_B_YAW_OFFSET 1 -3.180000000000000e-01

Sheila, Evan

Bat control is among the most challenging of control problems. In this case, some patience and a cardboard box were all that was needed to solve the problem.

Evan, Stefan

When we came in the winds were relatively high, so we decided to take another loock at the AS_A_36 phasing. We did so in DRMI.

- To take out the effect of WFS centering and the otherASC loops, we lowered the total ASC gain by a factor 10, and increased the WFS centering gain from 1 to 200 (raising the centering gain by a factor of 20).
- We then drove the SRM at 0.3Hz in PIT and YAW.
- Interestingly PIT and YAW totaly disagree on the phase, by about 125deg...
- Attached are screen shots for the old phases (picture 1), phased for PIT (picture 2), and phased for YAW (picture 3)
- Additionally, while all 4 quadrants show a reasonable signal for PIT, the YAW signal is weak in quadrant 1 and not present in quadrant 2
- We decided to make a pragmatic choice:
  - For PIT AS_B_36_I is already a fine signal - only for YAW it doesn't work
  - Thus we decided to phase AS_A_36_I for YAW...
  - ... and only use quadrants 3 and 4 (the lower two quadrants).
  - Quadrants 3 & 4 also have a similar strength signal (with opposite sign) and similar RF offset (with the same sign)
  - So: this new YAW signal AS_A_36_I should be fine now.

YAW Input matrix for I and Q now is:
H1:ASC-AS_A_RF36_I_MTRX_2_1    0
H1:ASC-AS_A_RF36_I_MTRX_2_2    0
H1:ASC-AS_A_RF36_I_MTRX_2_3    -2
H1:ASC-AS_A_RF36_I_MTRX_2_4    2

With this new YAW sensor we updated the ASC sensing matrix (pictures 3 and 4).

This sensor seemed to do a good job at 17W and at 24W. However at 24W we still saw a 0.4Hz instability - see next alog.

Nutsinee, Elli

When we arrived the IMC was not locking so we changed some settings to get it to lock.  Changed PSL differacted power to 7% up from 3% by changing H1:PSL-ISS_REFSIGNAL to -1.96V.PSL.  The PSL power was 1W when 2W  was requested at the rotation stage.  So we searched for home, and now requested power matches again.

We tried to lock the arms in green without success.  The X-arm PLL was not locked, we changed Crystal frequency to 100MHz and now it is locking, however the ALS_XARM and Y_ARM guardian still report faults "PLL; PHD", and "Ref. Cav. Power", which we couldn't fix.  We noticed the reference cavitytTPD has dropped from 0.85 to 0.7 V in the last 24 hours (see plot.)

We aligned the corner station optics using the oplev trend to where they were last night in order to do the HWS alignment.  We noticed BS oplev Yaw is showing zero as output.  Without the green from the arms this alignment was difficult.  in any case, we are starting to think that this HWSY alignment is proving too difficult with the current (wrong) in-vacuum lens installed-  the beam return beam is the same size as the mirrors we are using, and we have never been able to get rid of clipping patterns on the beam.

Nic, Sheila, Evan, Stefan

- Turned on ITMX PIT oplev (ITMY PIT OPLEV was already on)
- DC coupled SRM PIT oplev turned on.
- Tried new SRCL input matrix YAW:
   AS 36    AI    AQ     BI    BQ         
   OLD:   -0.6   0.3    0.3   0
   NEW:    0     1.0    0     0
- This seemed better at higher power for RF offsets, but is too early for judgement.
- Also tried new SRCL input matrix PIT:
   AS 36    AI    AQ     BI    BQ         
   OLD:    0     0      2     0
   NEW:   -0.5  -0.5    0     0
- We didn't keep this one though because it seemed worse at low power.

- Attempts later tonight were hampered by winds up to 30MpH in the corner.

We've noticed two more examples of epics channels freezing for a few seconds.  Yesterday (July 9 16:25:09 UTC) and tonight (0:22:49 UTC July 11)

Nic, Sheila

We put an excitation into the HAM6 ISI ISO Y filter bank, (30000 counts at 0.3 Hz) from about 3:17-3:19 UTC July 11.  We then did a by eye fit  (on a log log scale)for a fringe wrapping model.  We expected the excitation to result in 30 um motion of the OMC, but we had to use 36 um to get the fringe speed right. We get an amplitude reflectivity of 1.6e-7 for the single pass shelf. (compare to 1e-5 measured in 17919)  We see no evidence of a second shelf or a shelf in the null stream.  

We plan to make measurements in exactly the same was as 17919, if we get a chance again tonight.

Leonid.Prokhorov, Jeffrey.Kissel

We continue the charge measurements on ETMs. The data are beginning to be consistent with a small increase in charge, consistently negative.
For the past few weeks since the discharging the charge has been small (<10 [V] Effective Bias Voltage), and roughly consistent with a parent Gaussian distribution with a mean about 0.0 [V] Effective Bias Voltage. However, as we get more data, we're beginning to see a case for a slow negative charging of the test masses (about 2-5 V/week) in at least half the quadrants (ETMX UR, UL, and LR; ETMY (the pitch estimates of) UR, UL, and LR). The uncertainty of these measurements is too large to state that the trend is statistically significant, but yellow flags have gone up. 

This argues that we should continue roughly daily (say, thrice a week) measurements of the charge, and we need to continue to do so for another week or three.

There are three sets of plots, each which show the same data in a different way:
(1) ETMX.png & ETMY.png show the "raw" data, where the result of each estimate of the effective bias voltage shown *since* the discharging. Each single data point is an estimate of the effective bias voltage, i.e. the charge, as determined by driving the test mass while varying the requested bias voltage and measuring the response with the optic's optical lever.
(2) ETMX_Mean.png & ETMY_Mean.png shows both the mean and standard deviation, and weighted mean and sqrt(weighted variance) of the charge measurements for a given day (which can be from ~4 to ~15 of these 12 minute measurements per mean point). We believe this better shows the long-term trend of the charge.
(3) ETMX2015.png & ETMY_2015.png shows the mean charging measurement results since January 2015, i.e. it includes data when the test masses were charged and shows the discharge which happened in Mid-June.

(evan jenne nic)

We wanted to investigate the OMC alignment/backscatter problem. Driving the OMC SUS in Yaw has been known to cause backscatter noise due to the modulation of the optical path length when the OMC moves in Yaw.

Our procedure was to lock the vertex optics in a bright michelson configuration (a state has been added to the IFO_ALIGN guardian to make this easy). Then we wanted to drive the OMC in yaw and choose the yaw->longitudinal matrix element such that the center of rotation would be about the input beam, rather than the omc center of mass. This would be determined by minimizing the scatter as measured by either OMC trans, or the MICH error point.

I was surprised that we were not able to induce any significant backscatter fringe wrapping noise in this configuration. We drove the OMC SUS in longitude up to the point that the beam was misaligning enough to noticibly affect the OMC DC trans.

We also drove the ISI table directly by putting a 1Hz 1mm injection into the Y isolation loop error point. 

Driving the path length, we both listened and had a live spectrum running. We saw no evidence of scatter in either OMC trans or MICH_IN1.

We will need to think if there is another configuration (available to use without arms) that will be more sensitive to backscatter.

Calibration Team

Sign of h(t):

The gravitational wave strain h(t) is given by  h(t) = Delta L/L where Delta L  is is computed using

                         Delta L = ± (Lx - Ly)

The sign of Delta L can be determined using Pcal actuation on the test mass. Pcal only introduces a push force  so pcal readout signal (truly pcal excitation) is minimum when the testmass is away from the corner station (closer to pcal laser). From the first plot the phase between DARM/PCAL is ~ -180 degrees (DARM lags PCAL) which suggests that DARM signal from ETMX will be maximum when pcal is minimum (ETMX further away from corner station). Similarly, from second plot, since DARM and PCAL have a phase difference of ~-360 degrees (essentially 0 degrees), the  DARM signal from ETMY is minimum when the pcal is minimum. This shows that the sign convention for the Delta L is '+'

Time Delay between Pcal and DARM:

Also the slope of the curve gives the time delay between Pcal and DARM signal chain. The time delay is about 125±20 us. This time delay can be accounted for, within the uncertainity, from the difference in signal readout chain outlined in Figure 3 attached.

Refer to LLO alog #18406 for the detailed explanation behind this  conclusion.