J. Kissel, P. Thomas

Given that we've had so many examples of rocker switch death this evening (see LHO aLOG 20839), I was able to identify that my new(ish) warning message about this failure mode on the MEDM overview screen (see LHO aLOG 20281) had a bug. The MEDM logic was watching L2 for all three stages, L2, L1, and M0. I've committed the bug-fix to the SVN such that LLO can receive its benefits.

Stefan, Evan

This is an analysis that Daniel suggested a while ago.

When we increase the interferometer power from 3 W to 24 W, we increase the common-mode radiation force on the test masses. Since the suspensions are compliant, this produces an extra displacement in the test masses along the beamline relative to their suspension points. The CARM loop senses this common-mode displacement and compensates by applying a slow control voltage to the IMC VCO. This control voltage is offloaded to the UIMs of the end station suspensions, and then subsequently to the endstation HEPIs, thereby moving the suspension points of the ETMs forward so as to cancel the radiation-induced displacement. Therefore, an appropriately calibrated HEPI tidal signal can be used to estimate the amount of power circulating in the arms.

We looked at a data stretch from 2015-08-07, when we had been sitting at 3 W for a while and then powered up cleanly to 24 W, and found the following:

• The HEPI tidal signals show a nice, linear trend for the hour preceding and the hour following the power-up [first attachment].
• By fitting the linear trend [second attachment] and subtracting it off [third attachment], we can get an estimate of the HEPI displacement due to the radiation pressure alone. The displacements are 2.9 µm each for X and Y.
• During power up, the change in the force on the test mass due to the change in radiation pressure is ΔF = 2 ΔP / c. The dc compliance of each test mass is H = Δd/ΔF = 2.6×10⁻³ m/N, where Δd is the change in displacement of the end-station HEPI. Therefore, the power change is given by ΔP = c Δd / (4 H) [there is an extra factor of two here because there are two suspended masses per arm]. From this, the power change per arm is 85 kW.
• From the IMC input PD we know that the power ratio before and after powering up is P₂/P₁ = 10.3. This can be combined with the above power change to arrive at an absolute number for the circulating power: 94 kW.

On the other hand, when we make a similar estimate from the end-station QPDs, we have something like 24 W × 0.88 × 1/2 × 40 W/W × 283 W/W = 120 kW. [The factor of 0.88 is the modecleaner transmission.]

The calibration of the HEPI tidal signals into nanometers is sort of loose [to within 10%?], according to Hugh. Similarly, there is some spread in the power inferred from the endstation QPDs, which gives an uncertainty that is also on the order of 10%. With a more precise HEPI calibration, perhaps we could use this method to better constrain the optical calibration.

J. Kissel

For efforts of limiting systematics in the calibration, I've measured all ISC controlled stages of ETMY drivers, UIM, PUM, and TST. For now, I just attach screen shots of the measurements and report where they live, such that LLO might repeat exactly the same measurements tomorrow (instead of their current plan to take the measurements in analog, lugging around an SR785). In the fullness of time, I'll fit these to get precise poles and zeros for use in the DARM model.

I can already tell that they will be different from what has been quoted as cannon -- LLO aLOG 4495 -- which is upon what all ETM current *coil* driver compensation filters are based. For example, for some reason, the z:p = 50:300 [Hz] filter on the output impedance network of the UIM drivers, seems to have disappeared. It was supposed to have moved up in frequency when we increased the drive strength (see T1400223 and E1400164) but not disappear. It shouldn't matter for the calibrating, but this is just rediculousness that should be investigated lest we're being misinformed about the frequency region we do care about by a bogus measurement.

Anyways, I'll do a similar study to what was done in LLO aLOG 4495 with this data, and we will compensate the calibration accordingingly.

Details:
------------------
In order to 
(1) speed up measurements 
(2) focus drive amplitude and number of cycles in the frequency regions which were needed, and
(3) yield the ability to do multiple slow measurments simultaneously
I split the measurements for each driver into several templates with differing frequency bands. Ideally, if I weren't inventing, completing, and hoping to analyse it all to give me a very precise result in one day, I would have used the SEI group's Schroeder-phased TF tool, which has such flexibility, but alas.

The templates live and have been committed to here:
/ligo/svncommon/CalSVN/aligocalibration/trunk/Runs/ER8/H1/Measurements/Electronics/
For ESD Driver in low-noise configuration:
2015-08-24_H1SUSETMY_ESDLVLNDriver_WhiteNoise_0p5Hzto1kHz_$(QUADRANT)_TF.xml
2015-08-24_H1SUSETMY_ESDLVLNDriver_SweptSine_50Hzto1kHz_$(QUADRANT)_TF.xml
2015-08-24_H1SUSETMY_ESDLVLNDriver_SweptSine_500Hzto7kHz_$(QUADRANT)_TF.xml

For ESD Driver in high-range configuration:
2015-08-24_H1SUSETMY_ESDHVDriver_WhiteNoise_0p5Hzto1kHz_$(QUADRANT)_TF.xml
2015-08-24_H1SUSETMY_ESDHVDriver_SweptSine_50Hzto1kHz_$(QUADRANT)_TF.xml
2015-08-24_H1SUSETMY_ESDHVDriver_SweptSine_500Hzto7kHz_$(QUADRANT)_TF.xml

For PUM Driver (each template covers all quadrants)
2015-08-24_H1SUSETMY_PUMDriver_SweptSine_0p1to30Hz_$(FILTERSTATE)_TF.xml
2015-08-24_H1SUSETMY_PUMDriver_WhiteNoise_1to7000Hz_$(FILTERSTATE)_TF.xml

For UIM Driver (each template covers all quadrants)
2015-08-24_H1SUSETMY_UIMDriver_WhiteNoise_0p1to900Hz_$(FILTERSTATE)_TF.xml
2015-08-24_H1SUSETMY_UIMDriver_WhiteNoise_0p1to7000Hz_$(FILTERSTATE)_TF.xml

Regarding the system set-up, I took advantage of the secret coil driver switching ability (revealed in, for example, on page 8 of G1401184), to turn off the digital compensation filters, and drove through the either the ESDOUTF bank for L3/ESD or the TEST bank for L1 and L2. Note, though I turned off the frequency dependent compensation, I did not turn off any of the OUTF gain and sign compensation (which is why some of the PUM and UIM driver's signs are flipped with respect to each other). I'll take this into account during post-processing.

Also, I've used the 65 [kHz] IOP test point SUS AUX monitor channels as my response channels. I discovered all too quickly that we've been running all of our AUX monitor models at 2048 [Hz].  Sadly, because we ('ve been told we) must develop a very precise inverse actuation filter for the hardware injection team, we need to get information about the high (but not super-nyquist) frequency poles which we compensate for in the DARM ESD path (namely, the ~3250 [Hz] zero -- see LHO aLOG 18769 and LHO aLOG 18579). Not only does a sampling rate of 2048 prevent measuring such zeros, there's also severe distortion from the 65 [kHz] to 2 [kHz] very aggressive IOP down sampling filter. Yes, we know the shape, but it's just much less confusing to not include it in the measurement. However, comparing the IOP test points against the user model versions of the channels did provide good sanity checks. It for example allowed me to identify that -- even though we fixed the user-model channel ordering of the monitors for the low-noise driver, we haven't yet fixed them for the high-voltage monitors, so the Lefts are still reversed from the Rights.

Jeff K. reports that the ETMX UIM driver has tripped. Cheryl reported this happening last Sunday: alog 20808

From plotting the L1 OSEM monitor signals it appears that it tripped on Aug 25 2015 03:08:25 UTC. (plot attached)

Daniel, Dan, Stefan

I used the 45MHz modulation depth reduction in alog 20777 to fit the amount of 45MHz sideband on the ASC-AS_C_SUM diode:

reduction   ASC-AS_C_SUM cts
 0dB           38430
-1dB           32630
-2dB           27460
-3dB           23680

This suggests that we have the equivalent of 8796cts of power that doesn’t respond to the 45MHz modulation index reduction, plus 29735cts of 45MHz sideband power (at 0dB reduction).
Thus 29735/38430 = 77% of the total light is 45MHz sideband, and 23% is something else (mostly carrier).

For the ASC_AS-C_SUM calibration I get:

4e-4          fraction of HAM6 light on AS_C (alog 17738, super-seeds 15431)
x 800V/W      PD gain (alog 15431 -> 200V/W, but in the digital system we do not divide by 4)
x 10^(36/20)  whitening gain
x 1638.4cts/V ADC gain
= 33080 cts/Watt_HAM6

I get under nominal conditions (23W, Gamma=0.3, 0dB reduction):
899 mW of 45MHz light (compare that to an expected 23W(INPUT)*(.3)^2/2(MOD)*0.88(IMC)*0.89(NOM IFO TRANSMISSION) = 811mW)
and
266 mW of other light (carrier junk?).

20mA of light on the OMC_DCPD transmission, corresponding to about 25mW of "good" carrier light - 10 times less than the junk.

Also, if I use the calibration of the ASC-AS_C-SUM diode, normalizing it by the 29735cts of 45MHz SB, I should get a calibrated (power) RIN sensor.
I can look at the driven oscillator amplitude noise transfer function to x-check this: I would expect the power RIN / amplitude RIN TF to be equal to sqrt(2).

(Note: Daniel's RIN sensor calibrated in Vrms/rtHz / Vrms - a sqrt(2) of my previous alogs, which all quote RIN as Vrms/rtHz / V_pk, being equivalent to a rad_rms/rtHz number. )

I indeed get 1.4. (plot 1).
Plot 2 shows the same transfer function but using only the seg1, with the IOP channel (H1:IOP-ASC0_MADC6_TP_CH11). Again, 1.4.

Now things hang together...

(Sheila Evan Daniel)

The ASC-AS_B_RF45 sensor is currently not used for the auto-alignment. To investigate, if centering on the 2Ω is different from DC, we temporarily cabled its LO up to 90MHz. To revert back, remove the output cable from the 9MHz (currently 90MHz) distribution amplifier in ISC R3 (slot 37) and hook it back to the 45MHz distribution amplifier in the same rack (slot 33).

This sensor had the analog whitening stage turned on and the digital anti-whitening stage turned off. Turned on the digital anit-whitening.

ssh, who and man commands all returned: 'Input/output error' but ps and grep commands worked
Firefox did not launch
gpg returned an error
I talked to Dave. He suggested I power cycle the computer and log in as myself instead of ops. I am going to use my own account for my shift.

Attached is a shot of the white board for tomorrow.  Let's green up the SDFs tonight as several restarts are in the offing.

J. Kissel, S. Dwyer, E. Hall

As I was about to characterizing the ETMY coil drivers (i.e. the UIM and PUM), I noticed that they were in their highest noise state. After conversations with Sheila and Evan, we (re)agreed that the PUMs should be run in their lowest noise state, which is with  LP ON and ACQ OFF, or State 3 from T1100507. As such, we've switched all QUADs to this state, and confirmed that ISC_LOCK guardian will ensure this to be true in the future (again). That guardian has been reloaded.

The reason they had been put back into high range (and taken out of the guardian) was that the range was needed to better damp the QUAD roll modes after they had been severely rung up in the Christmas Episode in early August. 

From a calibration stand point, this will affect the DARM calibration by a small amount, but I had not started characterizing the ETMY PUM drivers before I got started, and I'm now full aware of it, so it's affect will be fully understood and expected. As such, we're OK with this configuration change. Further, we'll all be happy with the little bit extra range we get from it (Evan will post an aLOG making a noise statement later)!

Calibration Measurements:

- Kiwamu, IFO down for calibrations, 9:05 - expected to be all day, continuing now

*** FYI, I move the IFO to Commissioning when this happened and should have been Calibrations - my bad.

Note; We are now in Calibration, so IFO has two states:

'"IFO is up'"  OR  "IFO is having calibration measurements run."

Today's parasitic IFO/site activities:

- JeffB to EY, dust monitor investigation, 9:07 - done

- Hugh to EX and EY, HEPI, 9:07 - done

- JeffK, ETMY, measuring coil drivers, 9:15

- Sudarshan, PEM channel check in LVEA, 9:20 - done

- TJ EX BRS reset - 9:54 - done

- Kyle, near EY (Y28) to gather stuff - done

- Dave, EX, drawing updates - 12:10 - done

- Kyle, near EY (Y28) to gather stuff, 12:54 - done

- more visits to end stations while there was the opportunity, but no changes, just monitoring or restoring equipment.

Currently no outstanding IFO issues.

Calibration measurements continue.

Stefan, Elli

On Saturday Stefan measured the AS36 signals with dither lines from the BS and SRM (alog 20777):

Lines:
H1:SUS-SRM_M3_ISCINF_P_EXC 7.0Hz, 300cts
H1:SUS-SRM_M3_ISCINF_Y_EXC 7.5Hz, 900cts
H1:SUS-BS_M3_ISCINF_P_EXC  8.0Hz, 100cts
H1:SUS-BS_M3_ISCINF_Y_EXC  8.5Hz,  30cts

Here are some plots of the AS36 signals demodulated against these line frequencies.  These signals  show how the sensitivy of the AS_36 WFS to the BS and SRM, which changes during the heat-up stage of the whole interferometer, and during 45MHz modulation depth reduction.  Attached are plots of the original and demodulated signals vs time.  Two vertical red lines are plotted; the first corresponds with when the IFO reaches full power, the second is when the 45MHz modulation depth reduction begins.  At the end of the time series the traces go crazy-  this is where Stefan reports lock was lost due to SRC1 yaw run away.

The following WFS channels are fed back to the optics at this point:
AS_B_RF36_I_PIT      >>   SRC1 PIT      (seen in demodulation of 7.0Hz line. Right two plots, red trace)
AS_B_RF36_I_YAW   >>   SRC1 YAW    (7.5 Hz line.  Right two plots, blue trace)
AS_A_RF36_I_PIT      >>   MICH PIT       (8 Hz line. Left two plots, red trace)
AS_B_RF36_Q_YAW  >>  MICH YAW    (8.5Hz line.  Right two plots, brown trace)

The SRC1 PIT signal doesn't change much, which is good.  SRC1 YAW has a 180deg ohase change during the heat-up stage.  Lines 1813 and 1815 of the guardian indicate a sign change in the ASC input matrix, maybe this corresponds to this phase change (?).  MICH PIT signal looks pretty good, getting close to 180deg phase at the end of the modulation depth reduction.  MICH YAW drifts downwards in phase, it looks like it hit -180deg just at the point we lost lock.

Jim, Evan

We have grown tired of the glitching in the PRM M3 LL OSEM, so here is a script that ramps it off in full lock. It gets rid of the glitching and allows us to recover 60ish Mpc range.

Also included is a screenshot of the usual Euler/OSEM matrix for PRM.

This entry is meant to survey the sensing noises of the OMC DCPDs before the EOM driver swap. However, other than the 45 MHz RFAM coupling, we have no reason to expect the couplings to change dramatically after the swap.

The DCPD sum and null data (and ISS intensity noise data) were collected from an undisturbed lock stretch on 2015-07-31.

Noise terms as follows:

• Shot noise
  • For 20.0 mA dc on the DCPD sum, we expect a shot noise of 8.0×10⁻⁸ mA/Hz^1/2.
• Dark noise
  • Dan and I measured this a few months ago. In full lock we use one stage of whitening, which amounts to a dark noise of 1.5×10⁻⁸ mA/Hz^1/2 or so above 100 Hz. We have at times experimented with two stages of whitening, but it requires some vigilance regarding the violin modes.
• Intensity noise
  • Coupling was measured à la Kiwamu by leaving the outer loop off and driving the inner-loop excitation point. For the noise estimation, I used the outer loop out-of-loop sensor. Since Sudarshan et al. previously found that this is artificially high, this estimation is an upper limit (though probably no more than a factor of 3, given Sudarshan's plot).
• Frequency noise [CARM sensing noise only]
  • Previously (i.e., when we locked CARM using the in-air REFL sensor), I estimated the coupling by looking at the TF in-vac REFL to DARM, and for the frequency noise estimation I used the noise of in-vac REFL as an upper limit for the frequency noise. Since we now lock with in-vac REFL, which has more light on it than in-air REFL does, I do not expect that the noise of in-air REFL is a particularly useful upper limit for the frequency noise.
  • Therefore, I have tried to instead estimate the sensing noise in CARM (from in-vac REFL, the summing-node board, the common-mode board, and PDH shot noise) in V/Hz^1/2 and propagate it (using the Izumi/Sigg expression) into a frequency noise in Hz/Hz^1/2. For the CARM optical TF I use 12.7 W/Hz at dc, with a pole at 0.48 Hz.
  • Then I have injected noise into CARM and looked at the TF from the residual of the excitation into DARM. This is the coupling TF needed to propagate the estimated sensing noise to DARM, assuming the CARM gain is high (this isn't quite true at high frequencies; the ugf is 17 kHz or so, and the gain does not exceed 20 dB until 3 kHz).
  • Since this includes sensing noise only (and not, for example, FSS noise), I have labeled it as a lower limit. In fact, the coherence between REFL 9Q and the DCPD sum is about 0.04 around 7 kHz, perhaps suggesting a frequency noise contribution of 2×10⁻⁸ mA/Hz^1/2 or so. More investigation required.
• Oscillator phase noise [not included here]
  • Stefan and I measured the coupling of the 9 MHz RF source into DARM, and using the expected performance of the OCXO estimated the noise in DARM should be 2.8×10⁻¹⁰ mA/Hz^1/2 at 1 kHz. This is quite low (and not shown on the plot).
  • This number should be replaced with Alexa's and Daniel's measurements of the phase noise. An even more satisfying number could be made by trying to measure the 9 MHz and 45 MHz phase noises in situ, closer to the EOM (e.g., at the output of the distribution system on the ISC rack).
• Oscillator amplitude noise [45 MHz only]
  • In this case we know that the 45 MHz RFAM is the dominant contributor (other than shot noise) to the DARM noise above a few hundred hertz. Here I use Stefan's estimate of the RFAM-induced photocurrent (1.8×10⁻⁸ mA/Hz^1/2), which (as he notes) is not enough to explain the excess between sum and null.
  • However, based on tonight's measurements using the new EOM driver readback, it seems that 45 MHz RFAM is enough to explain the excess. Perhaps Stefan's measurement is an underestimate, since it was done at the output of the distribution system and did not include the final rf amplifier before the EOM.
  • As for 9 MHz RFAM, Stefan and I made an estimate of the coupling from the 9 MHz source into DARM. Based on the specified performance of the OCXO, the expected noise in DARM is quite small. However, it would be better to look somewhere further downstream, as Stefan did (although I think he said the measurement was not that clean). This noise is not estimated in the plot.

The downward slope in the null at high frequencies is almost certainly some imperfect inversion of the AA filter, the uncompensated premap poles, or the downsampling filter.