Since May 23rd the WI CO2 laser power started to fluctuate, probably due to the temperature changes of the laser  (see the first plot in attachment).

Thus, we decided to decrease the chiller set point from 18.86 °C to 18.76 °C in order to stabilize the CO2 laser temperature (~ 20 UTC, second attached figure).

Today at 14h36 UTC, WEB and NEB PCal fast processes have been enabled to monitor some channels with the LED flashing the IRIG-B signal on PD2.

Most of the FdIO servers have been restarted with the new release v8r36p5 based on  Cm  v8r14p3 and  Cfg v8r08p1

Here the list of the VPM  subsystem where the FdIO servers were upgraded

• Storage - stol03
• storage - stol0l2
• storage - stol01
• Data Access
• Data Collection

The Fbs servers were restarted too with a new release v8r16p1 using the Fd latest version

Several trials were made , triggering some lost of data in the data streams. Here the report for the RAW stream on stol02

Start> GPS 1271913300 - first frame  26 Apr 2020 05:14:42 UTC  (26 Apr 2020 07:14:42 CEST)
Last> GPS 1274072700 060 - Expected GPS 1274072760 found 1274072830 - miss 070s (0.01944h)
Last> GPS 1274428800 030 - Expected GPS 1274428830 found 1274428910 - miss 080s (0.02222h)
Last> GPS 1274429100 050 - Expected GPS 1274429150 found 1274429210 - miss 060s (0.01667h)
End  > GPS 1274444830 - last  frame  25 May 2020 12:26:52 UTC  (25 May 2020 14:26:52 CEST)
Period: 2531530s - 29.3001 days - 0.96066 months - missing 210s - 0.00243056 days

We started some leak testing activities at NE and CB, taking normally until the middle of next week.

* Some auxiliary pumps have been switched ON in CB and in NE *

- NE cryo turbo ON: V21 backvolume pumping started
- UHV24 switched ON @ 2400W : 1.2E-9 mbar
- UHV24 switched ON @ 2400N : 2.4E-9 mbar (backvolume pumping to be done)

The main issue with the RMS values in the entries above is not the calibration but a bug in dataDisplay.

Figure 1 shows the RF spectrum of B2 and the time series in dataDisplay.

Figure 2 shows the same computed from data in matlab. The spectrum is exactly the same. The correctly computed RMS is shown in red and the way it is computed in dataDisplay is shown in yellow. The difference is that dataDisplay forgets that the sample data has gaps, so the spectral resolution is not 1Hz but much poorer than that. All the RMS values are wrong by a factor 110 because of this. This also shows that the voltage RMS is not the right quantity to look at for saturations. The voltage RMS is computed to be 0.1V but the peak value of the time series (figure 1) is slightly above 0.2V. If the signal was a pure sine wave at 0.1V RMS should give a peak value of 0.15V. But here with have several RF frequencies that can add up coherently (depending on the phase between them).

Then looking at the calibration. The DAQ corrects for the gain of the variable gain stage. However the demodulation mezzanine has an additional total gain of 4.5dB due to the (VIR-0215A-20), and the LNA on the photodiode PCB (ABA-52563) has a gain of 21.5dB, so in total a 26dB gain. This means that a 1mA of RF current, converted by 50 Ohm resistor, yields a voltage recorded by the ADC of 1V. Below the PD response pole (~12MHz) 1mA of current correspond to an optical power of 1.296mW assuming a 90% quantum efficiency of PDs. This means that the calibration factor for the RF data should be 1.296 mW/V, whereas it is 2.59 mW/V in the configuration file. So wrong by a factor 2.

This factor 2 error is also visible on the spectra level, see figure 4 for an example. B4 PD1 has a power of 40mW, which should give a shot noise at 1.15e-7 mW/rtHz, instead the spectrum is shown at ~2.5e-7 mW/rtHz because of this factor 2 error in the calibration.

Figure 3, coming back to the B4 PD1 data which close to saturation, they are reaching 0.8mW with the wrong calibration factor. So they correspond to 0.3 V in the DAQ before calibration, 0.4V at the input of the VGA (AD8370) and 0.2V at the output of the LNA (ABA-52563). The VGA has been measured to saturate at 0.75V (1.5 Vpp) in low gain mode, 0.375V at the output of the LNA because of 6dB gain of the transformer in front of the VGA. while for the LNA the 0.2V is a factor 5 below the 1dB compression point at 10dBm (1V amplitude). So it seems the VGA starts to become non-linear from our point of view for signals that are slightly less than a factor 2 smaller than the saturating amplitude.

For O4, the new VGA ADL5205, has been measured to saturate at 2.8V (5.7 Vpp, after taking into account the 3dB gain of the transformer in front of the VGA), so that is the maximum voltage that can be sent out by the LNA, a factor 7 increase over the current situation. The new LNA (PHA-13LN+) has its 1dB compression at 16dBm instead of 10dBm, which correspond to an amplitude of 2V. So the LNA will become the new limit on the dynamic, with a total improvement of a factor 5, assuming the 1dB compression will not spoil to much the signals.

OB IP has been centered with motors since horizontal corrections were starting to saturate.

We just realized that there was an error on the x axis due to the sampling frequency of Hrec. I attach here the correct projections.

For B1p there are two photodiodes, PD2 sees 10 times less power than PD1, and it has notches at 2MHz, 6MHz and 12MHz.

Figure 1 compares B1p PD1 and PD2 in broad band. As expected the 56MHz is smaller in PD2 by a factor 10 compared to PD1, because of the lower power.

Figure 2 zooms into the 1-20MHz region. The 6MHz is a factor 200 smaller in PD2 (10 due to power and 20 due to notch), the 2MHz is smaller by more than a factor 200 for the same reasons. The 12MHz is smaller only by a factor 100, so the notch might be less effective and provide only a factor 10 of attenuation.

In B1p PD1 the 6MHz is comparable to the 56MHz, so with 13dB of modulation it would be a factor 3 higher and cause issues, as the line height would be at 3mW RMS, the 12MHz would stay more manageable at 1mW RMS.

Figure 3 shows B2 PD2 in a wide frequency range and Figure 4 zooms into the 1-20MHz range, that photodiode has notches at 16MHz, 49MHz and 61MHz. The 2MHz and 14MHz have a height comparable to the 12MHz and 16MHz, which are roughly equal, so this is just the beat between the 6MHz and 8MHz. The only unexpected behavior is that the 2MHz is a factor 2 higher than the 14MHz, this is due to the 14MHz being reduced by the 16MHz notch. This factor 2 is already present when the 6MHz modulation is at -28dB (blue curve). Note that there 2MHz harmonics at 4MHz, 10MHz, 18MHz, ... I expect this is due to the VGA which has a gain setting 10 times higher than for other PDs and is known to have distorsion at the ~50dBc level (VIR-0215A-20).

A concern is that B2 PD2 sees currently only 3mW of power, and for O4 we plan to increase this by a factor 10. This would bring the spectrum RMS 3mW when the 6MHz is reduced to -28dB, so already at the limit of what the new RF read-out chain could handle. Furthermore, increasing the 6MHz modulation from 3dB to 13dB would put the 12MHz at 20mW RMS, the 2MHz at 20mW RMS, the 6MHz at 6mW RMS and the 14MHz at 6mW RMS. It would also bring the 56+/-6Mhz at 2mW RMS each. So even by adding notches at 2MHz, 6MHz and 12MHz (which would also reduce the 14MHz by a factor 2-3), it would bring the total RMS to ~5mW, probably slightly more than the new RF read-out chain can handle. And also this would bring the number of notches from 3 to 6, while only the space for 3 notches is available on the PCB.

Note that in this and the previous logbook entry I have misread the label of the y axis. So the power should be in uW and not in mW. However, this powers seems far too low for me, so I expect the calibration factor into mW to be wrong.

I have looked over the whole O3a period at the family of lines initially described  by entries 45223, 45230. The separation (with respect to their central frequency) is 9.9918 Hz and two sub-families exist: a) those placed a bit before integer 10 Hz (e.g. 89.9255 Hz, 139.8842 Hz, 169.8594 Hz,…); b) those placed a bit before integer 5 Hz (e.g. 134.8882 Hz, 164.8635 Hz,…).
Their persistency as a function of the line frequency follows a rather clear path: the lines start to be visibile around 44.9 Hz (with persistency ~0.15), becomes stronger and are very well visible in the range (roughly) 119.9 Hz -> 299.75 Hz (with persistency 0.3-0.8), then decrease and disappear around 550 Hz. Overall, there are about 100 lines (a+b).
Each line is in fact a quadruplet with an apparently constant structure. For sub-family a) the separation among the first and the second peak is 6.1E-4 Hz, while the separation among the 2nd and the 3rd, and the 3rd and the 4th, is 3.05E-4 Hz. For sub-family b) the four peaks are symmetric with respect to the central frequency with separation 6.1E-4 Hz among the 1st and the 2nd, and the 3rd and the 4th, and separation 3.05E-4 Hz among the 2nd and the 3rd. Overall, each quadruplet covers about 2 mHz. The persistence and strength of each peak in a quadruplet depends on the line frequency.
Fig. 1 and 2 show an example of lines belonging to the two sub-families. Plot 3 shows the peakmap (collection of points in time-frequency) for the line at 164.8635 Hz. Plot 4 approximately shows the time dependence of the persistency for the same line. This behaviour is similar to those of all the other lines (at least, of those I checked).  

The data with the increased modulation depth of the 6MHz in LN3 to 3dB (purple lines in the figures) can be compared to the normal conditions with -28dB modulation of the 6MHz (blue lines).

In the figures we compare two photodiodes B4 PD1 and PD2, which see the same power. The differences are that PD2 has an analog notch at 6MHz, which reduces the line by a factor ~20. Also itis a 3mm diameter photodiode compared to 2mm for PD1, which means that above ~20MHz the response of the PD2 photodiode is a factor 2 smaller than of the PD1 photodiode due to the photodiode capacitance.

Figure 1 shows the broadband RF spectrum, the dominant lines are the 56MHz+/-6MHz, 12MHz and 6MHz. On PD2 the 56MHz+/-6MHz lines are a factor 2 lower due to the PD size. The 12MHz line is about the same in both. And the 6MHz is a factor 20 lower in PD2 due to the notch.

Figure 2 zoom into the region between 1MHz and 20MHz. Comparing purple and blue the 12MHz line is increased by a factor 1000 as expected from the 31dB increase in modulation. The 6MHz, 2MHz and 14MHz are increased by a factor 30 in both photodiodes, also expected from the 31dB increase in modulation. The 14MHz and 2MHz are the beat notes between the 8MHz and 6MHz, in principle the height should be half way in between on a log scale between the 12MHz and the 16MHz, hower they are almost equal to the 16MHz, a factor 3 smaller than expected. The probable reason is that the overlap between the 6MHz and 8MHz beam shape is poor, of the order of 50% in amplitude (so ~30% in power). The only sign of non linearity in PD1 on that figure is the small line 4MHz.

Figure 3 zoom between 2MHz and 50MHz, there are several lines which are much higher in PD1 than in PD2, the 3*6MHz line is a factor ~20 higher, and the 7*6MHz is a factor 10 higher. The 5*6MHz line is a factor 4 higher. The 4*6MHz and 6*6MHz line are a factor 2 higher in PD1, but that is expected due to the larger size of PD2. An additional 2dB of 6MHz modulation was causing PD1 to saturate, so this increase in odd harmonics of the 6Mhz shows the beginning of the distorsion in the signal due to non linearities close to saturation, not however that these harmonics are over 2 orders of magnitude smaller than the 6MHz itself.

2mW RMS of RF spectrum appears to be a limit of this photodiode design. It consistent with LNA (ABA-52563) data sheet saturating at 1V RMS, assuming there is no other gain factor than the 2.592 into the DAQ. The notch at 6MHz on PD2 is able to reduce this RMS by a factor 2 to ~1mW. The next three contributors in PD1 are the 12MHz, 50MHz and 62MHz which each contribute ~0.7mW RMS, for a total of 1.2mW RMS (in PD2 the 50MHz and 62Mhz are smaller due to the PD size).

The biggest limitation to increasing the modulation depth is the 12MHz as increasing the modulation to 13dB would increase its amplitude by a factor 10 to 7mW RMS. So a notch at 12MHz would be definitely needed to reduce the amplitude to 0.4mW RMS. An already notched 6MHz would increase by a factor 3 to 0.3mW RMS. Notching the 50MHz and 62MHz, is impossible without removing also the 56MHz. So these would increase each of these sidebands 2.1mW RMS, for a total of 3mW RMS. The LNA planned for O4 (PHA-13LN+) starts to distort signals for a 7dB higher signal according to the data sheet. So should be able to handle 4.5mW RMS with the same distorsion as seen here for PD1 with 2mW RMS. So a notch at 6MHz and 12MHz with the new LNA should be able to handle 13dB of 6MHz modulation with a factor 1.5 of margin with regard to the start of distorsions. However, the power increase from 25W to 40W is equal to that margin of 1.5. So keeping the power at 40mW on these photodiodes may be needed, by dumping some of the power on SPRB on a beam dump.

Figure 4 shows the situation for B1. The 6MHz saturates the photodiode with 4mW RMS. The new high finesse OMC design will reduce the 6MHz power on B1 by a factor 10. Also signal recycling will reduce the amount of 6MHz reaching the photodiode by another factor 8, as the 6MHz is not resonant in the SRC. This gives in total a decrease by a factor 80 in power, or a factor 9 in the 6MHz beat with the carrier. If the 6MHz modulation depth is increased to 13dB, the 6MHz beat would increase by a factor 3/9, and the 12MHz would increase by a factor 10/80. In total this would give 1.3mW RMS on the photodiode for the 6MHz, and 0.04mW RMS for the 12MHz. The filtering of the 56MHz will not change for O4, but the power of the sidebands might increase by a factor 5. This would bring the 56MHz to 0.3mW RMS. In conclusion notches should not be necessary for the B1 photodiode in O4, but we might consider it as a precaution for the 6MHz, if it doesn't have an impact on the squeezing signal planned for O4 at ~4MHz.

Analysis remains to be done for B1p and B2.

The servers TCSChillerNI and TCSChillerWI have been restarted at 8:08 UTC after a crash.

The chillers have been checked this morning; everything was working properly.

MC IP has been centered with motors since horizontal corrections were starting to saturate.

The local control noise review VIR-0369B-20 has shown that the TZ control injects a lot of the local control sensing noise above 10Hz and shakes the bench, especially at 30Hz and 170Hz. This was a known problem in 2018 but has been forgotten since. Changed the roll-off to the same as used for TX so that this doesn't get forgotten again between now and O4.

10:03 UTC new filter active and loop closed

10:13 UTC opened SDB1 angular control loop

Figure 1 shows that the feedback noise is reduced by more than a factor 10 at 30Hz and 170Hz compared to the reference used in the noise review.

The output of the DAC driving the OMC PZT is monitored by the ADC, this gives us a direct measurement of the DAC noise. The OMCs are not locked, so at present the only signal is the small (0.01V in amplitude) line at ~10kHz driving the OMC length to generate an error signal.

10:49:20 (5min) - reference data (purple)

11:49:20 (5min) - added a 1V offset to the OMC PZT (brown)

11:55:20 (5min) - added a 3V offset to the OMC PZT (green)

12:00:40 (5min) - added a 3V offset to the OMC PZT, ~10kHz line amplitude set to 0 (blue)

12:06:10 put back the OMC1 offset to 0V and OMC PZT ~10kHz modulation to 0.01V

Figure 1 and 2 shows this measurement. The DAC noise has permanetly a level of ~3e-6/sqrt(f) V/rtHz above 10Hz. In addition, when there is an offset present, there is a low frequency bump below 10Hz, which grow in amplitude with the offset. There is also a bump at ~450Hz growing, but this is due to the voltage reference of the ADC (see VIR-0216A-20 ) so it is not a noise of the DAC. There are also some 100Hz harmonics growing with the offset. It is not clear to me what is its origin, but it is not due to the ~10kHz modulation line, as switching this line off doesn't have any impact. Above 2kHz the noise is flat at ~1e-7 V/rtHz, this is the level of noise of the ADC, so it is not clear what is exactly the DAC noise level, but it must be below that level.

The 3e-6/sqrt(f) V/rtHz dependence confirms the measurement performed before installation at LAPP

The BRMSMon VPM server has been restarted twice this morning to update the list of input channels.

Today only the SDB2 and SPRB power supplies are monitored .

The follwing plots show the spectrum time of the  SDB2_LEFT_DOWN +12V and the SPRB_LEFT_DOWM +12V channels in the [80Hz-110Hz] and in the [130Hz-160Hz]  frequencies bands.

On can see :

• that the 1Hz  comb  disappears when the SPRB DBox LED were switched off around 13h20UTC
• The presence of some moving lines on both SDB2 and SPRB power supplies
  • for SDB2 around 95Hz and 150Hz
  • for SPRB around 86Hz with some jump upto 92Hz , and 142Hz with some jumps upto 149Hz

The first plot show, for the whole tests sequence related to 5Hz comb investigation,

• The ITF state (META_ITF_LOCK_index)
• the spectrum time of the +12V power supply related to the DBox hosting the camera mezzanine board (SDB2_POWERSUPPLY_DBOX_RIGTH_DOWN_p12V)
• and the one of the B1p QD2 quadrant horizontal signal demodulated at 56MHz (SDB2_B1p_QD2_H_56MHz_I)
• according the following states:
  • Camera ON or OFF
  • Mezzanine Camera ON or OFF . When the mezzanine camera is OFF the connected cameras becomes OFF too .
  • and DaqBox LED ON or OFF

Note:

• the camera trigger signal is a square signal at 5Hz: so only  the 5Hz odd comb(1*5Hz, 3*5Hz, 5*5Hz, ..)
• it seems that time axis of the spcetrum time plot is shifted related to the real one

1:  From 7h00UTC  to 9h15UTC

• During this test sequence, the 5Hz comb remains present in SDB2_B1p_QD2_H_56MHz_I spectrum until the ITF unlock, as there is no more signal
• From the SDB2_POWERSUPPLY_DBOX_RIGTH_DOWN_p12V spectrum, one can see that
  • the 5Hz odd comb amplitude reduction when stopping one by one the different cameras but the 5Hz comb remain present
  • the 5Hz even comb amplitude disappears only if the Camera mezzanine is OFF
  • Around 8h55UTC the DBOx LED were switched OFF on all the SDB2 DBox: the 5Hz comb disappears on all the SDB2_POWERSUPPLY_DBOX_XXX_p12V  signals

2: From 10h00 UTC to 11h00UTC - ITF back in low_noise_3

• The DBx LED are OFF on all the SDB2 DBoxes
• when the CAMERA are OFF and the Camera mezzanine OFF too(from 10h20UTC to 10h30 in the spectrotime plot), there is no more 5Hz odd comb in the  SDB2_B1p_QD2_H_56MHz_I spectrum and  in the  SDB2_POWERSUPPLY_DBOX_RIGTH_DOWN_p12V one
• from 10h30UTC to 10h50UTC the cameras were set to ON one by one with only one enable each time. One can see that the 5Hz odd comb reappears in the  SDB2_B1p_QD2_H_56MHz_I spectrum.

This plot  (zoom) compare the spectums of B5_QD2 DC and RF at 56MH channels, and the ones of the B1p_QD2 DC and RF at 56MHz in the following conditions:

• Blue: DBox LED ON , mezzanine camera ON and  camera ON,
• Purple: DBox LED OFF , mezzanine camera ON and  camera ON,
• Brown: DBox LED OFF , mezzanine camera OFF as consequence  camera OFF,

with:

• for the B5_QD2  photodiode
  • the DC signals are acquired by a ADC2378 located in the SDB2_DBOX_RIGTH_DOWN DBox
  • the RF@56MHz signals are acquired by a DemodMezz located in the SDB2_DBOX_LEFT_UP DBox
• for the B1p_QD2 photodiode
  • the DC signals are acquired by a ADC2378 located in the SDB2_DBOX_RIGTH_UP DBox
  • the RF@56MHz signals are acquired by a DemodMezz located in the SDB2_DBOX_RIGHT_DOWN DBox

The plot (zoom) related the SDB2 +12V power supplies in the same conditions

One can see that

• for the B5_QD2 the 5Hz odd comb disappears on most of  the DC and the RF channels once the DBox  LEDs are OFF
• for the B1p_QD2, the 5Hz comb are still present but  are reduced if there is only the DBox LEDs off . They disappeared only if  everything is OFF : mezzanine camera(cameras ) and  DBox LEDs.
• for B5 and B1p quadrants, the 5Hz even comb remains at the same level whatever the conditions.
• related the power supplies:
  • for the SDB2_DBOX_LEFT_{UP,DOWN} and SDB2_DBOX_RIGTH_UP  the 5Hz odd comb disappears when the DBox LEDs are OFF
  • for the SDB2_DBOX_RIGTH_DOWN the 5Hz comb (odd and even) disappears only  when the  camera mezzanine is OFF (cameras OFF too)
  • idem for the Quadrant power supply, the 5Hz comb (odd and even) disappears only when the  camera mezzanine is OFF(cameras OFF too)

SDB2 power supplies

These plots show the spectrum time plot of the SDB2 +12V power supplies between [30Hz-60Hz], [90Hz-120Hz], [150Hz-180Hz] . One can see

• some moving lines around 40Hz, 100Hz and 150Hz on all the channels monitoring related to the SDB2 power supplies
• and a line moving from 30Hz to 42Hz  in the SDB2_POWERSUPPLY_DBOX_{RIGTH,LEFT}_UP_P12V channels during the ITF relock at ITF state 124 (LOCKING_OMC1_B1s2_DC) . This does not occur at each lock sequence

Conclusion

The 5Hz comb in the SDB2 quadrant signals seems to be due a combination of  the cameras readout and the DBox LEDs.

SR vertical control was close to saturation (correction signal abot 9 V). Stepping motors of F0-F3 have been used to discharge the DC (500 steps CW). F7 loop has been closed for a few minutes to damp ty mode.