Jeff, Kiwamu,

In addition to the classic free-swing-Michelson technique, we did another calibration of the ETM responses using the ALS diff VCO.

We locked ALS diff and drove various stages of ETMs. The plan is to take out the loop suppression by using a measured open loop transfer function and calibrate data into meters through the known VCO calibration. The data and results will come later. A conclusion from todays's calibration is that the calibration of the ETMY ESD in the low voltage configuration is difficult to measure since the strength is so weak. So for the reason, we ended up measuring only the ETMY L2 stage and ETMX L3 stage. Sigh. In order to get a reliable calibration on ETMY ESD, we probably need the DARM loop closed in fully locked interferometer and need to make a comparison between well-calibrated ETMX ESD and ETMY ESD.

Adrew Lundgren has written a script that can be easily used to identify which suspensions saturate in which order in a lockloss.  The script is in USERAPPS/sys/common/scripts/ and should work for LLO as well.   The script is called with a time which can be either a gps time or any format that tconvert accepts, it checks for suspension MASTER_OUT_DQ channels that go above 2^17 for 10 seconds before or after the time given.  This may be integrated with the summary pages and/or the graphical lockloss tool soon, but now it is ready to go from the command line.  For now it is not checking things like RMs, OMs, IMs, but they can be added if anyone wants them. 

Thanks to Andy for putting this together so quickly, and to Jamie, Johnathan Hanks, and Greg Mendell for helping to get it running here.  

Keita, Kiwamu, Daniel, Elli

We have measured the SRC length to be 56.013+/-0.0035m.  This is 4.8+/-3.5mm longer than the design SRC length of 56.008m.   
This result is consistent with an earlier measurement of the LHO SRC length of 56.015(+/-.005)m (alog17451).  (This earlier measurement which was considered questionable due to signal-to noise issues and a lack of SRMI angular control.)

Method:
See alog 18263 DRMI was locked with wavefront sensors on for alignment control.  An auxiliary NPRO on IOT2R was sent into the interferometer through the back of IM4.  The Aux laser was coaligned with the PSL using the PSL transmission through IM4 onto IOT2R, and the prompt reflection of the Aux laser onto IM4. The auxiliary laser frequency was locked at a frequency offsets to the PSL using a PLL, and this frequency offset was swept to measure the Aux laser power reflected from DRMI as a function of frequency.

The DRMI reflection coefficient is a function of frequency because Mich reflectivivty varies with frequency. This is due to the 8.9cm Schnupp asymmetry, and Michelson reflectiviy = cos(2*pi*f//c*ScnuppAsymmetry). When DRMI is locked, the PSL light is totally reflected from Mich, and DRMI reflectivity looks the same as the PRC reflectivity.  At 842.7 MHz offset from the PSL frequency, Mich transmissivity is 100%, and DRMI looks like a cavity between the PRM and SRM mirrors and with the length of SRC+PRC combined.  As the PRC length is already known (alog 10642), we can measure the DRMI reflectivity around 842.7MHz by sweeping the Aux laser through +/-842.7MHz offset from the PSL frequency.

The reflected  beatnote of the PSL and the Aux laser read out at relfair path. The frequencies of the transmission dips closest to +/-842MHz were fitted using a lorentzian function. The number of fsrs (N) between peaks at ~+842MHz and -842MHz were determined.  This determines the fsr and the length of the combined PRC/SRC cavity.

df=positive_peak_frequency-negative_peak_frequency
vfsr=N*df
LSRC=c/2/vfsr-LPRC;

Analysis:

Graphs of the reflected beatnote power vs aux laser frequecy offset are attached.  There is an 11MHz osciallation in the reflected power which is not yet explained.   The phase has had a linear phase term removed, but is not continous from sweep to sweep, perhapse due to small changes in the alignment of the aux laser to the psl over time.  There are peaks which appear every fsr, which I am assuming ar ehigher order modes, but I haven't looked closely at these yet.
Peaks were fitted at -842.14(0.02)MHz and +841.933(0.02)MHz, graphs attached.  
The number of fsrs between these peak frequencies is 1277.  (If the number of fsrs wer off by +/-1, the cavity length would differ by +/-10cm.  We had already estabilished from previous measurements that the SRC length is not off by this much.)
This corresponds to a combined PRC/SRC cavity vsfr=1.319MHz, and length=113.664(0.0027)m.  The PRC length was already measured by Evan et al (alog 10642) to 57.6508+/-0.0007m, so the SRC length is 56.013+/-0.0035m.
 

[Morning Meeting]

SUS BSC 1 2 3 down

[Safety Meeting]

DON'T GET HURT!

[Activities]

8:41 Jeff & Sudarshan to EX (Calibration work)

8:45-9:20 Richard & Fili in CER working ITMX SUS

9:35 Richard to SUS 2B power (Electronics room)

10:00 Jeff & Sudarshan temprary back

10:12 Jeff & Sudarshan back to EY

10:28 Richard back

10:46 Rick et al. to EY to measure transfer functions

11:48 Fred and a guest to LVEA

12:16 Fred back

12:42 Jeff & Sudarshan back

12:58 Jeff B. to optic room

14:08 Kyle rolled up receiving door

14:17 Kyle done, receiving door closed

Happy Calibration Day

Will taking some current measurements for SUS racks this morning, Richard noticed that the ±24V power supplies for HAM4/5 (ISI Coil Drivers) had some oscillation in the current meter. We power down the ISI coil drivers (HAM 4 and 5), and the oscillation in the current meter disappeared. We powered the ISI coil drivers back on and oscillation in the current meter is no longer present.

There was an ADC timeout error in the h1susb123 I/O chassis at 23:26 PDT yesterday night (May 26), which caused all of the user models (h1susbs, h1susitmx, h1susitmy) to stop running. I restarted all models without power cycling the electronics and the models restarted correctly.

Sheila, Kiwamu, Evan

Using the same method as described here, we determined that the switching of the ETMY ESD low-pass filter appears to be working fine and is compensated for correctly in the ESD output filters. With offloading turned off and DARM controlled by ETMX, the transfer function ETMY L3 LOCK L → DARM IN1 is identical in both LPF states. It very similar to the transfer function ETMX L3 LOCK L → DARM IN, up to a constant factor of −50. This is a little mysterious to us, since we expect only a factor of 20 at dc between the high-range driver and the LVLN driver.

Anyway, we partially transitioned control of DARM to ETMX and ETMY (we had them actuating with about equal strength), and then saw that the ETMY ESD drive rms was about 30 000 ct, with most of the counts coming from the 322 Hz and 538 Hz calibration lines. We turned the line amplitudes down by a factor of 10 (from 2 ct to 0.2 ct). However, h1susb123 went down right as we were about to complete the transition to ETMY.

- thunderstorm early in the shift, tripped a panel alarm in the fire system

- Fire Department here to reset the pannel

- full alignment of IFO, after opening shutter at EX, then handed off to Kiwamu

- JeffK was at EY

- CP2 still in alarm after being filled

- RO water system is in alarm

Evan, Kiwamu, Sheila, Jeff

We noticed that we weren't really driving ITMX PUM.  Evan and I went to the racks and saw that the DAC outputs were changing, but the LED that says DAC WD next to the DAC input was not lit and there was nothing coming out of the AI board.  This is probably why Dan was unable to damp ITMX violin modes last night.

D. Gustafson, K. Izumi, S. Karki, J. Kissel, R. Savage, D. Tuyenbayev

Stay tuned for more details on each, but since we have so little time during these three days we're taking the "take the measurement now, look at it enough to know *you're* happy, *then* think and document it once we don't have any more time" approach, so please be patient if our aLOGging falls behind our activities. As such, I'm going to try and keep up with this daily "debriefing" so at least all are aware of our progress.

We've begun this week's calibration measurement's by doing the most invasive stuff first:
K. Izumi, D. Gustafson 
     - Made electronics measurements necessary to use the ALS DIFF VCO as a calibrated frequency actuator and compare line(s) generated by this VCO against ESD calibration lines in the DARM ASD to assess QUAD's actuation strength. See LHO aLOG 18634.

J. Kissel, R. Savage, S. Karki, D. Tuyenbayev
     - Made SR785 measurements of all elements of the EY PCAL electronics chain, including the AA, AI, and full RX (reflection off of the test mass PD) and TX (a PD picking-off of the power transmitted into the test mass) that includes the PCAL interface chassis, similar to what has been done at LLO (see, e.g. LLO aLOGs 18106, 18199, 18309).

Goals for tomorrow:
K. Izumi (and whomever's willing to help)
     - Get a free-swinging Michelson measurement of all stages of the ETMY's actuators that are involved in the hierarchy

J. Kissel, S. Karki
     - Finish straight-forward electronics measurements for ETMX PCAL (i.e. the same that were done today at EY)

R. Savage, D. Tuyenbayev
     - Stay at EY and compare PCAL PDs against other broad-band PDs to assess frequency response of PCAL PDs.

For an overnight test we have moved the Rx detector assembly into the Tx module and directed both output beams into the detector.

We plan to restore the nominal setup tomorrow morning.

Note that the cover on the Tx module is ajar while we are making this measurement.

Dan, Kiwamu, Evan

Summary

Tonight we worked on getting the interferometer back to its low-noise state. We are stable at 10 W, but there is some instability at higher powers.

Details

ITM steering

First, at 3 W we manually steered the ITMs to a good recycling gain (38 W/W), and then updated the TMS QPD offsets. We also locked the arms in green, adjusted the green QPD offsets for maximum buildup, and then updated the ITM camera references. Then we re-enabled the ITM loops in the guardian. This allowed us to power up all the way to 21 W without significant degredation of the recycling gain.

After that, we were able to consistently engage the ASC with the guardian.

Power-up issues

However, we found that at 21 W the interferomter suddenly unlocks in a matter of minutes. There seems to be no instability in the arm or sideband buildups before the lockloss. We looked at OMC DCPD signals for signs of PI, but we did not see anything ringing up during any of our short high-power locks. Some times to look at are 02:29:50, 02:59:50, 04:57:30, 06:55:00, all 2015-05-26 UTC. But any of the other 21 W locklosses in the past 12 hours follow this pattern.

We measured the OLTFs of PRCL, MICH, SRCL, and DARM before and after powering up, but they all look fine and did not change with power. For CARM, we start at 3 W with a UGF of 14 kHz with 47° of phase. Then during power-up, the electronic gain is automatically adjusted to compensate for the increased optical gain. The algorithm for this was shooting a little high, so after power-up the UGF was more like 27 kHz with 30° of phase. This is probably fine, but we adjusted the algorithm anyway, so that the UGF is placed at 19 kHz, with 45° of phase. Anyway, this did not solve the lockloss issue.

We also tried locking at some lower powers. At 15 W the interferometer lasted for about 15 minutes before unlocking. At 10 W, the lock time seems to be indefinite (at least 90 minutes).

DARM crossover

Using FM9 in ETMY L1 LOCK L (zero at 2 Hz, pole at 5 Hz), we were able to push the L1 crossover from <1 Hz to 1.7 Hz by adjusting the filter gain from 0.16 to 0.31. Measurement attached, showing before and after. This is not included in the guardian. By pushing up the crossover, the rms drive to L2 decreases from >10000 ct to about 6000 ct or so.

Other

For the record, we did not notice any kicks to the yaw of IMC REFL tonight.

Sheila, Alexa, Evan

Summary

We have transitoned CARM from digital normalized REFLAIR9I to analog REFLAIR9I, with a 4 kHz bandwidth and 50 degrees of phase. An OLTF is attached [the last data point is spurious, so ignore it]. This lock started at about 2015-02-09 12:24:00 UTC. We are leaving the IFO locked.

There is plenty of phase to push the bandwidth higher, but we have encountered large offsets induced by switching on the common-mode and summing-node boards.

We can also improve the low-frequency fluctuations of the CARM error signal by introducing an integrator somewhere; we need more dc gain.

Details

Analog REFLAIR9I is plugged into input B2 on the summing-node board (SNB), with polarity "off". The output of B goes into input #2 on the common-mode board (CMB), with positive polarity. Digital normalized REFLAIR9I is plugged into input A1 on the SNB, with polarity "on". The output of A goes to input #1 on the CMB. [See LHO#16489 for a review.]

According to our reckoning, the shape of the digital CARM loop at the start of the transition is roughly 1/f above a few hertz. At a few hertz and below, it has a number of boosts and integrators which make it tricky to engineer a stable crossover with the analog signal.

Transition procedure is as follows, starting right after the guardian has brought the interferometer into resonance.

• With the B2 gain at 0 dB on the SNB, input B2 engaged on the SNB, and the input #2 gain at 0 dB on the CMB, we engage input #2.
• Step up B2 gain to 8 dB on the SNB.
• Turn off double integrator in digital CARM path (FM2 in REFLBIAS: it is two zeros at 2 Hz and two poles at 0.01 Hz).
• Step up B2 gain to 14 dB on the SNB.
• Remove zero-pole pair in digital CARM; it is a 1.6 Hz pole and 20 Hz zero. We remove this pair by engaging FM1 on REFLDCBIAS.
• Step up B2 gain to 17 dB on the SNB.
• Engage analog compensation filter in the CMB. It is a pole at 40 Hz and zero at 4 kHz.
• Ramp down digital CARM gain all the way to zero using the input matrix.
• Increase the analog CARM gain by 10 dB using the CMB slider. This is the point at which we saw disconcertingly large offset jumps. The total jump was 6 ct of REFLAIR_A_RF9_I_NORM. For comparison, the peak-to-peak fringing of this signal during digital CARM is 6 ct pkpk.
• We also saw a huge offset jump when turning off A1 on the SNB, which analogizes the digital CARM loop. In retrospect, this is probably because we had an integrated history on the output of this loop (since we turned the loop off at the LSC input matrix, not at the loop's output).
• To tune the error signal offset to zero, we have shifted around the common offset slider on the CMB

Also, the use of DHARD WFS (pitch and yaw) has removed the need for touching up the ETMs. However, since the AS36Q WFS feedback to the BS has not worked for the past couple of days, the BS had to be touched up by hand every so often.