Hang, Dan Brown

Only EY was down from this dolphin crash so this recovery was quicker than some of the others.

Initial alignment went fine except for PRC align. It seems the PRC1 filter changes made the other day  (46151) made it unstable for initial alignment, probably too much gain. In PREP_PRC_ALIGN Guardian we switched off all the filters apart from FM1 (-20dB), it converged slowly and with FM1 off it still works.

Only one ALS lockloss during LOCKING_ALS, DRMI locked in about 20s.

Took about 2 hours until we were up again - although most of that was checking CO2Y table for leaks and figuring out what was up with PRX initial alignment rather than the Dolphin crash itself.

I expect to me hear for ~90 minutes or so and will make a comment to this entry when I am leaving.

The pressure gauge at X2-8 location near X-end is reading high and might have failed in a new way due to lack of solar power. Adjacent pressures are normal so the control room can ignore this alarm. VAC team will investigate when on site.

Added 350 mL water to TCSY to bring level from 8.6 cm up to 10.1 cm today. This appears to be a higher-than normal drop over the last couple of days, with the caveat that the previous reading was without optimal eyeglasses. At a minimum, it seems wise to keep an eye on the readings.

Also, topped off Wallace with 50 mL.

Unfortunately our 25 day streak of no Dolphin crashes came to an end at: Dec 25 2018 08:56:14 PST

I've captured all the Dolphin and system logs. I'll work on restarting the models soon.

If anyone is in the control room today, please call my cell phone and we can complete the recovery.

This is new - no action needed at this time.

During the power up, there is some variation of the DRMI optical gains. This can lead to loop instability and lockloss. This could be mitigated by:

1. perfect TCS
2. digitally compensating the optical gain
3. or having a loop w/ more margin.

I have made a new low pass filter to give some more margin. Its more stable with no noise penalty, so it is now loaded by default.

Plots:

1. open loop gain: (green) old loop w/ 4 dB gain margin and 25 deg phase margin. New loop has more gain since the old LP filter had a DC gain of -2 dB(?).
2. comparison of old (CYAN) with new (Purple); ~ 10 deg more phase @100 Hz
3. comparison of spectra: old (right) and new (left). Basically none of the SUS DAC RMS is due to the high frequency stuff, so its OK to relax the low pass filter.

Rana, Hang

After adding the res G's at 0.47 Hz our ASC loops appeared to be quite and stable at 25 W for more than 20 mins. However, as we tried to power up to 28 W, our dithering loops, especially the yaw ones started to drift away. This then triggered the ~ 0.5 Hz oscillation in CHARD YAW and then in other ASC loops. In the second attempt we tried to increase the dithering loops gain as we power up. However this did not kept the dithering loops stable. While the error signal still crosses zero, the oscillation seemed to be growing. The further the soft dithering loops' error signal deviated from 0, the more sever the 0.5 Hz oscillation in CHARD YAW. Or it might be the other way around, as the CHARD YAW RMS increases, the spot motion naturally made the dithering loops oscillates more.

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In addition to power up, we also tried to go to LOWNOISE at 20 W.

In the lownoise asc state, we reduced the CHARD YAW dc gain to 0.7, giving it roughly 3 Hz UGF. Then we could re-engage the ELP10 (FM2) filter to reduce its noise.

However, we kept losing lock at LOWNOISE_ESD_ETMX, specifically when we tried to transition ETMX to ITMX+ETMY. The ITMX part seemed fine. The ETMY ESDOUTF_DC_OUTPUT was zero before the transition, which seemed weird. In the guardian there also seemed to be no explicit commands setting up ETMY ESD in that state.

Rana, Hang

Yesterday we saw the 0.47 Hz oscillation showing up in basically all the PIT ASC loops at 23 W and became unstable at 25 W.

We thus measured DSOFT P OLTF and the result was attached to this entry. The cyan/pink traces were some old measurements done back in October at 2 W. The OLTF measured today at 20 W was the blue/red traces (We have good measurement in the 0.3-0.6 Hz region yet below 0.1 Hz we could not get good). In both measurements  we saw a pair of zeros at 0.47 Hz, which was the freq we saw the oscillations.

To compensate for this feature, we put resgains at 0.47 Hz with Q of 3 and height of 12 dB in DSOFT P (FM9), DHARD P (added to the boost10W FM5), and CHARD P (added to boost10W FM5). The same filter was also created for CSOFT P yet it didn't seem necessary to engage it for now. After these changes the 0.47 Hz feature was basically removed from the PIT loops at 23 W.

An oscillation at similar frequency also appeared in CHARD YAW, and it was mitigated if we turned off the FM4 boost10W filter in CHARD YAW.

With those modifications we did not see oscillations at 23 W any more.

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In addition, we also improved our DSOPT/DHARD PIT decoupling for the B path (AC coupled; for damping the dPdTheta)

The new matrix we used for DSFOT P B path input was

In the second attached plot we compared the performance of this new input matrix to the old one (routed to DC5). The DHARD dither was at 23.3 Hz and the DSOFT dither at 21.1 Hz.

The new input matrix not only rejects hard mode much better, but also has a significantly improved SNR.

the interferometer locked by itself after we left this morning. It stayed locked for 10 hours (until the 6.4 EQ in Tonga a couple hours ago).

Some troubles re-locking:

1. arms locked green sort of OK although the ETMs are still swinging too much and there is lots of HOM green locks. The ALS unlocks drive up the ETMs; the damping settings ought to be made stronger for this part of the locking. ETMX in particular is kicked much more than ETMY.
2. ALS DIFF breaks the lock too much. Also there is something not right about ALS WFS scripting. The gain ramping or sequencing is off and often it comes on too slow to keep the y-arm locked.
3. sometimes there are Guardian thread exceptions related to channel access. I checked that these channels are responsive using 'caget' from terminal. Errors from log attached. Looking through  the logs its looks like this is happening on many of the attempts to go DOWN. IF this is not caught by a person, it could mean that the Guardian is not putting us back into the correct state for initial locking. Since the SDF is not up to date, sometimes our acquisition problems could be due to this. Perhaps we need some error flag (besides the error logs with a zillion lines of messages) if the Guardian fails to make its connections?

Contrast Defect Ratio at 2 W = 8.4 +- 0.2 ppm

Contrast Defect is as follows: 



The electric fields associated with this equation are shown in the fourth attachment.

When DARM is locked on RF at 2 watts and the OMC is locked, we get about 11.8 mA, or 14.0 mW of power on the OMC DCDPs.  This means the DARM offset is around 29 pm according to this plot.
During this measurement, we move the DARM offset from 29 to -29 pm and see what happens.

Procedure:
1) Lock OMC while DARM is locked on RF
2) Zero the QPD offsets for OMC ASC by switching to OMC dither alignment, zeroing, and moving back to QPD control
3) Zero the OMC LSC dither control signal by offloading to PZT2, then stop the feedback, parking the OMC on the carrier fringe
4) Change DARM1 TRAMP to 120 seconds
5) Move DARM1 OFFSET through zero (in this case from 9e-5 cts to -9e-5 cts)
6) Re-engage OMC LSC by stopping input, clearing history, unholding output, and restarting input.  This will find the fringe again quickly for the next measurement.

Parameters during measurement:
            Input Power  = 1.89 W
     PRG at 0 pm Offset  = 46.8 +- 0.1
      DCPD Responsivity  = 0.858 A/W
DCPD Quantum Efficiency  = 0.98
   OMC DCPD Dark Offset  = 7.2e-5 +- 3e-5 mW  (Found at the last time the IMC was OFFLINE)
      OMC DCPD NULL/SUM  = 0.0060 +- 0.0015
   Measurement GPS Time  = 1229475480


Differences between 0 and 29 pm DARM offset:
Value         29 pm     0 pm    29 pm/0 pm
------------------------------------------
PRG            46.5     47.0         0.99
TRX [cts]    1502.    1518.          0.99
TRY [cts]    1555.    1572.          0.99

Assumed to be one:
- IMC Transmission
- Input Faraday Transmission
- Output Faraday Transmission
- OMC Transmission
- Mode Matching

Not yet considered:
- RF45 Transmission through the OMC
- Source of contrast (differential lens)

Dark Port alogs:
45753 DARM offset calibration
45734 OMC DCPD Sum/Null Matrix