With a lock stretch of over 7.5 hrs at ~23.2W & a range of ~57Mpc, here is a picture of last night's lock stretch.  Just before 9am, H1 lost lock (no obvious reason, as we continued operating in an Undisturbed state),  the Intent Bit was taken to Commissioning, and Ellie started SRCL work. 

• SEI:  MICH Freeze measurement if allowed.  Only have one STS in LVEA. 
• SUS:  Nothing
• Facilities:  Hanging CR pics, cleaning outside window
• Vac:  Nothing
• PSL:  Nothing
• Outreach:  10-12:30 group of visitors
• CDS/Elec:  Rolling stuff in to H1 Room
• Visitors:  RichA, Steve V, Bob T, Peter F

Sheila, Evan, Stefan


- Reduced the whitening gain on both AS 36 ASC diodes. The new value is 24dB. We increase the input matrix values from 1 to 2 to compensate (for MICH and SRC1, i.e. the SRM loop).
- We tried to phase the AS_A_36 quadrants by wiggling SRM in yaw and pitch, maximizing the I signal. Not sure how meaningful that was though, because the actual signal we ended up using was Q.
- We switched the the sensor for SRC1_YAW (SRM) to 0.3*AS_A_36_Q + 0.3*AS_B_36I. This signal clearly reacted to our mysterious SRC cavity drifts, and had zero offset at the good locking point.
- We increased the power to 23W. This is the maximum power currently available. With this new SRM yaw sensor the 23W was very stable.
- The DARM offset was 14pm (or 1e-5 cts).
- This gave us a recycling gain of 38.
- Measured the open loop gain and verified the calibration.
- This configuration was stable for 1h.
- We took SRCL noise injections at: 8:46:15UTC and 8:59:40UTC (SRCL cut-off filter off and on)
- We took MICH noise injections at: 8:52:15UTC and 8:55:40UTC (SRCL cut-off filter on and off)
- Pushed the intent bit at 9:06:30 UTC.

- The inspiral range seems quite remarkably flat at 57 Mpc. A stron indication that we are now purley electronics noise limited at low frequencies.

To do tomorrow:
- Explore DARM offset: the new OMC code is ready to install, and will allow on-the-fly OMC offset tuning.
- Add the new ASC INMATRIX to Guardian.
- Add the new DARM offset to Guardian.
- Generate noise budget.

Tonight Dan went through some of the old violin mode damping settings, we have had all violin mode damping disabled for the past several weeks in the guardian since we improved the recycling gain.  Dan found that the old settings work for 6 of the modes, ITMY mode 3,5 and 6, ETMY mode 5, and ITMX mode 3 and 6. For ITMY mode 4 we need a sign flip in the gain.  All of the ones that Dan checked I put back into the gaurdian, some of which now have lower gain than before.  I also added ETMY roll mode damping back in the guardian.  

the remaining roll modes are at 13.89 and 13.98 Hz, but we don't know which is from ETMX and which is from ITMX

We had set up a DARM cavity pole tracker last night (alog 18401). The plot below shows a first result from the cavity pole tracker which showed very interesting results.

Punchlines

• The DARM cavity pole became stable after Evan and Stefan put the offset in ASC-SRC1_YAW.
• Before the offset was introduced, it showed slow dfift which decreased the pole frequency from 350 to 290-ish Hz on a time scale of 20 minutes.

[Tracker setup]

We set up a lockin oscillator in the LSC front end model at 322.1 Hz (alog 18401). The excitation amplitude was set to 2 counts at the LSC DARM output. Through the LSC output matrix it excites ETMX and ETMY with outmatrix elements of +1 and -1 respectively. Since we use one ETM at a time for controlling DARM, this setup excites just one ETM by 2 counts. The audio demod phase was initially set to 0 deg so that we can double-check the phase rotation later on. The demodulation cos and sin gains are set to 1. In the I and Q demodulators, I put a 260 dB gain such that the outputs are human-readable. The low-passes are 0.1 Hz 4th order butterworth currently. The notch has been on all the time (alog 18401) so that the excitation is insensitive to the control loop.

[Calibration of the audio demodulation phase]

According to the DARM loop model, I was expecting a phase rotation of about +80 deg including the known time delay of 219 usec at the excitation frequency of 322.1 Hz. By the way, 219 usec is the total delay of the DARM open loop. However, for some reason, I measured the phase rotation to be -128.4 [deg]. The math I got this number is  phi = atan(measured Q phase / measured I phase). So something is not right. Due to this unknown phase rotation error, I ended up calibrating the audio demod phase using the information that the cavity pole was at 355 Hz at a particular time (alog 18420).

In the post-process, I rotated the demod phase by multiplying a rotation matrix to the I and Q signals such that the demodulated signals has the effect only from the DARM optical plant, or in other words, I subtracted the phase rotation which is not from the DARM plant. I had to rotate them by -86.2 deg in order to get 355 Hz for the data points at around May-15-2015 9:21:34 UTC which is the time when Jeff estimated the cavity pole to be 355 Hz. The advantage of doing this rotation business is that is makes the math easier. In this condition, in-phase signal should be

(in-phase) = G / (1 + (omega / omega_0)^2),

where G, omega and omega_0 are the optical gain, excitation frequency and cavity pole frequency, respectively. Similiarly, the Q phase is also easy;

(q-phase) = - (omega/omega_0) * G / (1 + (omega / omega_0)^2).

Taking the ratio of the two demodulated signal, one can obtain a clean quantity;

(in-phase / q-phase) =  - omega_0 / omega.

This essentially corresponds to doing some atan calculation to derive the phase angle. From this quantity, I computed the DARM cavity pole rfequency as a functin of time as shown in the above plot. I attach a second trend of some relevant channels in the same period.

Also, I changed the audio demod phase in the realtime system to -86.2 deg such that I don't have to do the same post data-massage.

Stefan, Dan

We have edited the common OMC model to enable the READOUT path that performs dynamic normalization as a function of DARM offset and input power.  The changes have been committed to the SVN.  The goal here is to allow changes to input power and DARM offset after we have switched to DC readout, so the power ramp-up and experiments to the DARM offset can be performed after we handoff to the OMC.

Essentially everything in the OMC-READOUT block has been modified, although the overall calculations still match those in T0900023 (except for corrections for the math errors found therein).  The changes are:

• All channels have been replaced with cdsfilt modules to enable ramping on the offsets.
• The switch between the simple scaling and the fringe scaling path has been removed.  We didn't like the hard switch -- our preferred replacement would be a ramping matrix of the sort found in the LSC model, but a change of this magnitude was a little intimidating, so we settled for two filter banks whose output is summed.  Now, to switch from one path to the other, we will ramp the gain on the filter modules for a smooth transition.  This isn't something we necessarily expect to do, but the option is there.
• Upper and lower hard-coded saturation limits were changed to be either very big or very small, so we don't wind up hitting our heads/toes on these hidden gotchas.

A screengrab of the new model block is attached.

We also edited h1omc.mdl to enable the power normalization inputs.  There are two power-related inputs to the linked omc.mdl library from h1omc.mdl, "TRX_IN" and "TRY_IN".  These inputs were grounded.  Instead of using the normalized arm powers (which is what we think was intended), we have routed the requested PSL power (PSL-POWER_SCALE, although this is called LSC-OMC_POWER_REQUEST in the top level of the model) to both inputs.  This channel was already available in the model, the arm powers weren't, we didn't want to add any IPC sender/receiver pairs today.

Models were rebuilt, restarted, and the DAQ was restarted as described by Dave.

One thing we forgot to add are some additional epics readbacks in between terms of the calculation, as sanity checks that everything is acting as we expect.  We'll edit the model later.

Dan, Jim, Dave

Two OMC model changes were made. Both required a DAQ restart.

The first DAQ restart proceeded normally, the second did not complete. h1dc0 reported a bad master file in its log files. In fact it appears that around this time h1dc0 attempted to start three times, each time creating a running configuration with either missing or corrupted master files.

We logged into h1dc0 as root and restarted the daqd process manually. This time the master file was read correctly and the DAQ restarted normally. We are unsure of the original problem, possibly an NFS issue between h1dc0 and h1boot?

Note that on both DAQ startups today, the broadcaster was the last to start. Normally it is the first to start.

Following up what reported by Jeff about the DARM pole frequency, the attached plot shows a simulation of the change in the pole frequency when the SRM is misligned. To move the pole down to 290 Hz we would need a misalignment of about 30 microradians. It seems a large misalignment to me, but at least in simulation it's not affecting much the error signals or the power buildups.

Elli, Nutsinee

The return SLED beam is now centered on the ITMX HWS. The QPD1 sum reads 1.71 (mean) and the QPD2 sum reads 1.32 (mean). Green light was resonates in both arms during the time of the measurement.

The current position of the HWSX lower periscope mirror is X: -286 Y: -927 and the current position of the HWSX upper periscope mirror is X: 300 Y: -300.

The Hartmann plate is off at the moment.

Stefan, Evan

Summary

Adding an offset to the error point of the ASB36I→SRM yaw loop reduces the SRCL→DARM coupling by 10 dB. It seemingly has the added benefit of fixing the slow drift in POP90.

Details

SRM yaw loop offsets

After several days of trying to do SRCL feedforward on a moving target, we decided to try attacking the SRCL→DARM coupling itself.

We started by applying offsets to the dETM loops, since Gabriele's simulation seemed to indicate that this could cause an increase in the high-frequency coupling. We applied offsets of several hundred counts (both signs) to dETM pitch and yaw, and then injected broadband noise in SRCL. We saw a reshaping of the noise (see attachments), but no overall improvement.

Then we moved on to offsets in the SRM WFS yaw loop. Here we saw a more promising improvement with a positive offset at the error point (see attachment). In the end we found that an offset of 2100 ct works best in terms of reducing the coupling at high frequencies. This also seems to coincide with minimal power in POP90.

POP90 stabilization

With this yaw offset engaged, it seems that the drift in POP90 mostly went away when the SRM yaw offset was engaged around 09:14:00 (attachment). There is still some drifting, but the timescale is much longer. Perhaps we are closer to optimal coupling of the 45 MHz sidebands into the SRC. This particular lock lasted for about 2.5 hours (it broke for unrelated reasons) and showed no sign of the POP90/ASB36I instability that we've seen this past week.

DARM offset and calibration

For some additional reduction in SRCL coupling, we tried locking with a smaller DARM offset (14 pm, not 7 pm as I said before) and then updated the calibration (FM10 in the sensing inversion of CAL-CS). However, I have reverted these changes. This means that in general you should not believe the recorded inspiral range for most of the night.

Guardian changes, other configuration changes

If LSC_FF is requested, the Guardian will proceed from DC_READOUT to LOWNOISE_ESD_ETMY to LSC_FF. If desired, one can make a pit stop at COIL_DRIVERS before going through LSC_FF.

I had wanted to add some Guardian code that steps down the TRX/TRY QPD whitening gains by 6 dB before the ASC comes on (and then adjusts digital gains accordingly), since the QPDs will saturate when powering up beyond 10 W. But it seems this makes the ITM loops unstable somehow. So I've left some commented-out code in DRMI_ON_POP and in the DOWN state.

In the ITM M0 lock filters, I moved the integrators from FM2 to FM4 and stuck +20 dB gains in FM2. Now we have some room to adjust the offloading speed.

The move of the piezo mirror from the top of the periscope to the table top (Link) left large features in DARM at least in part because a resonance of the mirror mount that replaced the piezo mirror mount, overlapped with a higher frequency periscope peak, just as the lower frequency resonance of the piezo mounting had overlapped with a periscope peak at lower frequencies. Figure 1 shows, in red, periscope spectra before tuning, and, in blue, after tuning. The idea was to move the optic resonances, indicated by the high DARM coherence in red at 340 and 390 Hz, into the red valley centered at about 310 Hz by adding weight.  The blue trace shows that the peaks were moved to 310 and 340 and the coherence with DARM was reduced.

Figure 2 is an “after” photo showing the weight that was clamped to the mirror mount to make this change. In addition, figure 2 shows the safety cover, which covers the vertical path of the beam, that is responsible for the peak just below 300 Hz. Unlike the rest of the periscope, this safety cover is not damped and definitely needs to be - the safety cover resonance is showing up in DARM.

I also added a little weight to the top of the periscope to reduce coherence with DARM at 190 Hz by splitting overlapping resonances. This also helped.

I think that the next step is to minimize jitter coupling from the PSL table to DARM, possibly by injecting a peak using the PSL piezo and modifying alignment to minimize the height of this peak in the IM4 pitch and yaw signals and eventually by minimizing the injected peak height in DARM. 

SudarshanK, DarkhanT

We introduced two Pcal lines at 240 Hz and 310 Hz on photon calibrator at Y end.  The Pcal lines are about a factor of 10 above the DARM sensitivity at those frequencies. We will look into any changes in the amplitude and phase of these lines to determine the the position of cavity pole frequency. The cavity-pole has been observed at frequencies listed in  alog LHO #18360.