These are the OpLev trends for the past 24 hours. Will review with the OpLev group.
Scott L. Ed P. Chris S. Frozen water in the D. I. tank made for a slow start this morning. Cleaned 50 meters moving south towards X-1-4 double doors. Tube pressures continually monitored by control room and frequently by the vacuum crew. Safety meeting this afternoon.
Early H1 DARM spectra showed strong coherence with the IMC WFS dc readouts, particularly in yaw. In DARM this showed up as a fairly smooth noise bump between 100 and 200Hz. It was thought this was input beam jitter caused by the input beam PZT mount (on the PSL/IO periscope). Since then, low pass filters have been added to the PZT driver outputs to reduce the PZT mount pointing noise. The attached plot shows the coherence between DARM and the IMC WFS dc channels for last night's lock. We no longer see the broadband coherence betwen 100 and 200Hz (though there is some in a narrower band around 175 Hz). But there is significant coherence in other frequency bands -- in particular around 250-270 Hz, and around 350 Hz. The only place that the coherence manifests as a real peak in DARM is at 285 Hz. At least some of this coherence should go away when the input PZT mount is moved from the periscope down to the table surface.
The attached plot shows the frequency of the IMC VCO, when the common tidal feedback path to the ETMs is running. At the beginning of the plot the offset in the IMC_F filter module was set to zero. This then puts the IMC VCO in average ~150 kHz below the fixed frequency oscillator which drives the fiber EOM. In the second half of the plot the offset was changed to -3500 counts and the IMC VCO shifted to ~200 kHz above the AOM frequency. Under nominal conditions the offset is at –1750 counts, which corresponds to roughly zero offset at the output of the filter module.
The important thing is to avoid a frequency crossings of these two RF sources, since this is one of the reasons for RF crosstalk into the laser frequency noise. We should probably try to move the IMC VCO frequency up by another 100 kHz to make sure we stay away from zero.
The COMM and DIFF VCOs are running at nominal 78.92 MHz. Since they implement two stages of the frequency-difference-divider, their range is no larger than ±150 kHz. Hence, they cannot reach the AOM frequency—or the IMC VCO frequency when it is above the AOM one. Once we are in full lock and the green beams are turned off, we need to make sure that these two VCOs are at least 10 kHz apart from each other. This should then prevent RF crosstalk by the VCOs from reaching the detection band.
Here is a plot from yesterday's lock showing a maximum frequency excursion of no more than 150 kHz over a 2 hour stretch.
The end station VCOs were using a lot of their range at low frequencies after switching to the common tidal feedback path. This was traced to a factor of 2 error in the Hz-to-µm conversion. I also increased the gain of the integrator to 0.03 Hz from 0.02 Hz to make it the same as the local feedback path. This reduced the required VCO range by roughly a factor of 2.
To set the DIFF/COMM VCOs to a predefined frequency, disable the input switch of the PLL and adjust its input offset. Both common filters need to be on for this to work, since we need a high DC gain. The input offset is divided by ~200 before it is applied. The mid range set point can be selected by enabling the optional daughter board and tweaking the VCO offset. Since we don't have a daughter board, enabling it will simply disable the output instead.
Parking the DIFF VCO (input enable: "H1:ALS-C_DIFF_PLL_INEN"; input offset "H1:ALS-C_DIFF_PLL_OFS"):
The VCO offset for the DIFF VCO was set to –1.864V.
Parking the COMM VCO (input enable: "H1:ALS-C_COMM_PLL_INEN"; input offset "H1:ALS-C_COMM_PLL_OFS"):
The VCO offset for the COMM VCO was set to +0.083V.
Daniel also adjusted the tune voltage we use for the DIFF VCO as a starting point, before we lock. We used to use 0, now we use -1.9V, which is included in the gaurdian now. This means that the locations where we can normally fin the DIFF beatnote have changed, now one is at around 1370-1386 while the other was at 0 - 20 counts offset in the DIFF PLL CNTRL offset. I've added these to the hardcoded list that the guardian uses.
I noticed that the Pcal Y (alog 16815) had been disabled since 9 am yesterday in local time. After chatting with Sudartian, I turned it back on this morning by enabling H1:CAL-PCALY_OSC_SUM_ON in the PCAL_END_EXC screen.
The peak height at 540 Hz seemed unchanged with a variation less than 1%, comparing todays' Pcal line and the one from Feb 21st. The peak height was 7.70031x10-18 m/sqrtHz in with 0.1 Hz BW, 70% overlap and Hanning window in H1:CAL-PCALY_X_PD_OUT with the nominal calibration (alog 16815).
The last time this diode was alive was back in July.
The noise during last night lock was much better and more stationary than what we had the night before that. Closing more ASC loop helped a lot.
The first attached plot compares the time series of the band-limited RMS in the 100-200 Hz region during the two lock stretches. Now the noise is lower and there is hardly any non stationary behavior.
The most nasty feature of the spectrum is likely related to violin modes. There is a forest of peaks around 500 Hz, together with all harmonics up to many kHz.
Here are the past 10 days trends.
model restarts logged for Tue 03/Mar/2015
2015_03_03 01:48 h1fw0
2015_03_03 07:14 h1lsc
2015_03_03 07:16 h1omc
2015_03_03 07:18 h1calcs
2015_03_03 07:22 h1susmc2
2015_03_03 07:24 h1calcs
2015_03_03 07:34 h1broadcast0
2015_03_03 07:34 h1dc0
2015_03_03 07:34 h1fw0
2015_03_03 07:34 h1fw1
2015_03_03 07:34 h1nds0
2015_03_03 07:34 h1nds1
2015_03_03 09:57 h1lsc
2015_03_03 12:05 h1broadcast0
2015_03_03 12:05 h1dc0
2015_03_03 12:05 h1fw0
2015_03_03 12:05 h1fw1
2015_03_03 12:05 h1nds0
2015_03_03 12:05 h1nds1
One unexpected restart. Maintenance day: ISC, SUS and CAL model changes with associated DAQ restarts. Beckhoff EX machine needed a reboot (fortnighly freeze), new Beckhoff PLC2 code went into all slow controls machines.
Alexa, Sheila, Dan, Gabriele, Evan
In full lock, we now have the following loops closed:
The first six of these are more or less identical to what we had last night (some of them have different gains). The SRM loops are new, and have bandwidths of 100 mHz or so, based on step response.
SRM pitch could also be accomplished with ASB36I; tonight it appeared identical to ASA36I except with opposite sign. For SRM yaw, only ASB36I was a good signal; ASA36I had a static offset which could not be affected by moving SRM. Perhaps for symmetry, we should use ASB36I for SRM pitch, as has been done in the past for DRMI+arms off resonance.
It was also possible to move SR2 and SRM so as to center the spot on AS_C. However, we have not yet tried to close a pointing loop from AS_C to SR2.
Starting around 13:06:46 UTC, we are on dc readout with the above ASC loops closed, and at 8 W input power. There does not seem to be any need to adjust optic positions by hand.
To do this, we closed our ASC loops (as above) at 2.8 W with rf readout. Then Dan slowly stepped the IMC power up to 8 W. Some 1 Hz ringing was visible in POP18 and AS90. The ringing went away after turning down the gains of the BS ASC loops by 20% or so.
It seems that the calibrated DARM strain above 1 kHz is below the GWINC 8 W curve, so this needs to be looked over before we start believing calibrated spectra, inspiral ranges, etc.
Attached is a plot of coherence between DARM and various LSC signals, and a summary of progress in the uncalibrated DARM error signal.
The DARM offset for our 8W lock is 2e-5 counts, the DCPD_SUM is about 16mA. The OMC-READOUT_SCALE factor is -6e-7, the LSC-OMC_DC_OFFSET is -1e-5.
At LLO they found that they needed to servo SR2 to ASC-AS-C QPD, with 'wide' bandwidth (1 Hz), before the AS36I WFS signal became a good one for SRM. See log entry 15840. Stabilizing the SRC axis with these loops is also credited for affecting the SRCL -> DARM coupling to make it go from being mostly non-linear to mostly linear, so that a linear cancellation of SRCL in DARM was effective.
Two more things we did last night:
When we were on resnonance and had several ASC loops closed with a very stable and good alignment, I updated the POP B offsets to center the beam before we closed the PR2 loop.
| POP B | Old | New |
| Yaw offset | -0.4 | -0.38 |
| Pitch offset | 0.3 | -0.03 |
The old offsets were set by Sheila when we had DRMI locked to a good alignment and first closed the PR2 loop.
On another note, we locked with the ETMY ESD bias off (we never feedback to ETMY), since Evan's NB plot showed we were limited by ESD DAC noise. However; this showed no improvement in the DARM noise spectra.
I reduced the amplitude of the OMC ASC dither lines today, to [33, 50, 100, 100] counts for the [P1, P2, Y1, Y2] error signals, which are injected at [575.1, 600.1, 625.1, 65.1] Hz. Along with the ever-increasing ASC goodness, this reduced the noise around the lines. The attached plot compares the sidebands
We didn't observe any ill effects from reducing the dither amplitude (the SIN and COS gains were increased to maintain the overall loop gain). At some point we should measure the loops again to check that the bandwidths are still in the tenths-of-Hz range.
In other OMC news, someone merged the H1 OMC_CONTROL medm screen with the Livingston version last week; this change has been backed out. It's not a bad idea per se, but there are some scripts and buttons used here that aren't used by L1, and vice versa, so things were a little confused. Also, the DCPD gains had been reduced to 1, from 1000, around 2:30 in the afternoon today. This change was also reverted (maybe from a bad burt restore?) to keep the DCPD SUM channel calibrated in milliamps (rather than amps).
For some reason the OMC-DCPD_SUM_OUT_DQ channel is no longer accessible via ezca read. This caused problems in the OMC_LOCK Guardian.
After maintence day this morning, the corner beckhoff was not restored. The ALS SHG was not working because the temperature was not controlled. Before we realized this we went to the table to investigate and tried to adjust the beat note alingment. Once the SHG was back on, the beat note stregth was low. Although this sounds impossible, the thing that seemed to fix the problem was unplugging the RF amplifier and plugging it back in.
Looking at the code I see that the save/restore was disabled for the TEC controller. Not sure why. Fix it (in svn) assuimg it was mistake.
I am concluding that the scale factor in the original calibration (alog 16698) was underestimated by a factor of about 2.4 in 2 - 20 Hz frequency band (meaning, the DARM spectra we had collected were too good). This was due to my inaccurate estimation of the ESD actuation response.
For the frequency region above 20 Hz, it has been underestimated by a factor of 3.2 when the PSL power stayed at 2.8 W and the same DARM offset was used. This was due to the inaccuracy in the ESD propagating into the sensing factor and also inaccuracy in the UGF location. I did not try to track how the sensing calibration should have been compensated as a function of the PSL power or the DARM offset (alog 16726).
I have updated the CAL-CS online calibration coefficients accordingly in both the sensing and actuation paths.
Pcal_Y seems to still indicate that the DARM spectrum is consistently too good by 40-65 %.
(ETMX response agreed the sus model by 40 %)
The day before yesterday, I had a chance to repeat the calibration of the ESD response of ETMX by locking the X arm with the IR laser. Comparison with ITMX at 13 Hz gave me an ESD response of 6.32 x 10-16 m/cnts in ETMX at 13 Hz. This is 1.4 times larger than the expected than the suspension model. Since I used alpha of 2.0 x10-10 N/V2 in the model, the measured response corresponds to a slightly larger alpha of 2.8x10-10 N/V2. With the right force coefficient of -124518.4 cnts applied on ETMX, I tested both the linearized actuation and non-linearized. They showed almost same strength in a frequency band of 10 - 59 Hz as expected but with the linearized version somewhat stronger by 3-ish % (see the attached) presumably due to the charge on the test mass.
Since the change between the linearized and non-linerized actuations is so small, I neglected this effect and kept using the transfer coefficient of the non-linarized version at 13 Hz.
(Estimation of the DARM optical gain)
Using the measured data taken by Alexa (alog 16805), I estimated the optical gain of the DC read out to be 9.09x10-7 cnts/m. To get this number, I first extrapolated the ESD response to some frequencies at around 20 Hz. Since the loop shape is already known, fitting of the open loop gives me the optical gain. I did eye-fitting this time. The UGF was at around 23 Hz in this particular data.
Since I was able to lock the interferometer at 2.8 W with the DC read out tonight, I cross-checked the DARM open loop. Running a swept sine, I confirmed that it sill kept the same UGF (see the attached below). Good.
(Comparison with Pcal)
First of all, one thing I have to mention is that, in an alog (alog 16781) describing the comparison between LSC-DARM_IN1 and PCAL is not a fair comparison because we know that LSC_DARM_IN1 was not well-calibrated. I checked the CAL-DELTAL_EXTERNAL_DQ at this particular time, but unfortunately the spectrum did not look reasonable probably because I was in the middle of changing some parameters in the CAL-CS. Instead, I looked into a different lock stretch at Feb-02, 5:13:11 UTC with the same IMC incident power of 2.8 W. The Pcal reported greater displacement by a factor of approximately 4.6 (see the attached below).
If I applied the new accurate sensing calibration, the discrepancy would have been a factor of 1.45 or 45% with the Pcal higher than the DARM spectrum.
To double check it, I checked the Pcal again during one of today's lock stretches at Feb-21, 10:04:05 UTC. One thing we have to pay attention is that the Pcal excitation frequency is now shifted to 540.7 Hz (alog 16815). I used the Pcal calibration formula that Sudartian posted in alog 16718 to get the displacement. The ratio between the Pcal and DARM spectrum was about 1.65 or 65% with the Pcal greater than the DARM spectrum. Even though the ratio is slightly different from 8 days ago or so, it still indicates that the DARM calibration is too good by several 10%.
The other excitation at 36.7 Hz (alog 16815) did not have signal-to-noise ratio more than 2 in the DARM spectrum due to high noise in this frequency region and therefore I did not use it this time. Nevertheless, the Pcal at this frequency was also greater as well. So the relation between Pcal and DARM spectrum is qualitatively consistent.
Here is a fresh DARM spectrum (from 2015-02-26 10:21:50 UTC) compared with the GWINC prediction. Between 1 and 3 kHz (where the spectrum looks reasonably clean and has the right shape for shot noise), the agreement looks good.
GWINC reports 9 Mpc from this measurement.
This is another detail point of this calibration log (for my self-justification).
In the ISC call last Friday, people pointed out that the first Pcal plot (link to the plot ) seemed greater by a factor of 10-ish than the calibrated DARM. Here, I explain that they don't differ by a factor of 10 but a factor of 4.6 as I declared in the original alog.
To be celar, I attach a zoomed version of the previous plot. See below.
Taking the ratio of Pcal/DARM, I again confrimed that the ratio is 4.6185. This is the number I quoted in the original alog. Here, I repeat a conclusion I said in the original alog: since we now know that the DARM calibration was off by a factor of 3.18 on Feb 12th, if we apply this correction the descrepancy between Pcal and DARM would have been a factor of 1.45 or 45 % with the Pcal greater.
We made two additional experiments with the unsuspended, isolated pilot (Corning ETM02) ITMY, in the west bay of the LVEA. (Moreno, Landry)
1) We applied FirstContact to the HR surface, let dry over 24h, measured no excess charge (no more than |3V| at 1" from HR surface, AR surface, and barrel), ripped the FirstContact off the HR face in ~20s *without* doing any TopGun ion gun blowing, and then measured the voltage 1" from the HR surface. We find the resultant charge negative, with a claimed voltage of ~-22kV, -22kV and -22kV at three points across the face of the optic. Assessing the AR surface, we find a voltage 1" from the AR face of -12.1kV, -12.1kV and -11.3kV.
2) We made another trial in which after FirstContacting, we removed the polymer film while TopGun blowing to neutralize the surface. We followed the same basic procedures as outlined in alog 13104, with slightly different timings. The primary change in the experiment was the grounding of the optical table, and the addition of a grounded Al foil shield (see photo attached). The addition of the shield and ground dramatically changed the behaviour seen in the prior experiment linked above: generally, individual measurements that took minutes to settle exponentially to some voltage now settled in seconds. Furthermore, the apparent long time constants for which it seemed necessary to continue with the ion gun (~9min total) were not observed in this experiment. We took 2 minutes to pull the FirstContact, which included a coincident 2 minute TopGun blow, plus one additional minute of TopGun blowing, and measured +18 to +30V at several locations 1" from the surface of the HR side of the optic.
We'll repeat experiment #2 one more time, with shorter intervals between electrometer measurements, to better understand the field sizes, signs, and time constants.
In our final measurement trial of Top Gun de-ionizing of this (FirstContacted) test mass, we used shorter de-ionizing times to understand how quickly charge was being neutralized. Times are impacted by presence of the partial Al shield (in place for this trial).
i) FirstContact was re-applied to the test mass. The test setup was the same as above, and per the photo: grounded table and partial Al foil shield, also grounded.
ii) We then pulled the FirstContact over a period of one-minute, with coincident TopGun de-ionizing.
iii) Measuring the voltage with the field mill 1" from the center of HR surface, we find +440V, and at the limb of the optic (top,right, bottom, left) of +290V, +385V, -12V, and +50V. The sign here is unexpected given prior measurements have shown that post-FC rip, the charge is negative. For the AR surface, we find 0V 1" from the center, and +30V and -20V near the limb.
iv) After an additional 1m of TG de-ionizing, measurements 1" above the HR surface show: +10V (center), +8V, +10V, +12V, +8V (limb top, right, bottom, left). The surface is effectively neutralized. The 1" measurments above the AR surface show +28V (center), 0V (top), +15V (bottom)
v) After an additional 1m of TG de-ionizing (now 3m total), measurements 1" above the HR surface show: +20V (center), +25V, +20V, +15V, +15V (limb top, right, bottom, left). The 1" measurments above the AR surface show +8V (center), +10V (top), +8V (bottom)
