C. Biwer, J. Kissel Taking advantange of single IFO time to run PCAL vs DARM hardware injections. More details later.
C. Biwer, J. Kissel Taking advantange of single IFO time to run PCAL vs DARM hardware injections. More details later.
Tuesday 29 September 2015 John and Gately replaced the vibration isolators on end instrument air compressors. So here I follow up the correlation between the glitches and the EX_SEIS_VEA_FLOOR_[X,Y,Z]_DQ commented by Joshua (21470). I have analyzed data from the 09/29 10.00 UTC before the repair and the glitches are totally visible. The data after the repair 09/30 10.00 UTC shows no trace of the glitches. I attach two images to show these.
Now that we've cleaned up all of our systematics from the DARM model and released the O1 version (see LHO aLOG 22056, I've updated the diagram that explains how the actuation path clock cycle delay is derived, and also shows that the current value of 7 [clock cycles] or 427.3 [us] that was recently installed at both sites (LHO aLOG 21788) still does a fine job at approximating the total delay between the inverse sensing and actuation chains.
A good diagram on the timing of a hardware injection through the DARM path: LLO aLOG 22361
[Aidan, Alastair]
We ran a calculation of the coupling of intensity noise to displacement noise for the CO2X laser at LHO. The details are as follows:
"The absolute coupling is very low right now due to the small amount of power being used to heat the test masses. The transfer function has not been directly measured but we have an estimate for it in the following document:
One lock loss today due to an earthquake in Mexico. LLO also lost lock around the same time. The IFO recovered and relocked with relative ease. We have been locked at NOMINAL_LOW_NOISE for the past 2.25 hours. The Intent Bit was set to commissioning from 18:23 to 19:41 while Sheila was running some tests. The Intent Bit was set back to Observing at 19:41 (12:41)
Note:
In the attached, left is the trend of 45MHz signals after the driver swap in the PSL room. Signals named MOD_RF45 are from the PSL room, MOD_9MHz are actually from the old unit now installed in CER (and it's not 9MHz, it receives 45MHz signal from the 45MHz distribution amp).
Anyway, the new driver remained very glitchy for 6 or 7 hours but we don't see any correlation with the CER unit, then it became quiet for the rest of the night except three easily visible glitches. The largest one was about 0.06 counts pk-pk in the control signal.
But the old driver had good and bad period. For example the day before (middle panel) it was mostly quiet, but three days ago (right panel) it was nasty, and the largest glitch there was about 0.14 counts pk-pk.
Two things we learned so far are:
We made a test with the CER unit by changing its output termination. Nominally, it runs into 50 Ohms. In the attached plot just before 70s the terminator was removed briefly and put back again. This resulted in a up-down glitch. Then, this was repeated around 80s. Between 200s and 210s the terminator was removed and replaced by a cable with clips attached to the end. The clips were then shorted repeatedly resulting in pairs of down-up glitches. Looking at alog 21789 and its second attachment we can see two up-down glitches—albeit at a much smaller scale.
Keita went out during a lockloss and started tapping at different points in the RF distribution chain of the 45.5MHz RF signal.
No effect:
Effect similar to what we see:
Effect much larger than what we see:
Only the removal of the terminator was seen in both units. The other glitches were only seen by the unit which is fed by the tapped cable or connector.
The most sensitive point was the tapping of the elbow indicating a possible connector, cable or adapter problem nearby. We should probably redo the extension cable which was inserted to account for the phase delay.
Title: 09/30/2015, Day Shift 15:00 – 23:00 (08:00 – 16:00) All times in UTC (PT) State of H1: At 15:00 (08:00) Locked at NOMINAL_LOW_NOISE, 22.4W, 71Mpc Outgoing Operator: TJ Quick Summary: Wind is calm; no seismic activity. All appears normal.
Title: 9/30 OWL Shift: 7:00-15:00UTC (00:00-8:00PDT), all times posted in UTC
State of H1: Observation Mode at 75Mpc for the last 6hrs
Shift Summary: I had one lockloss, but it came back up with relative ease. The RF Noise wasn't bothering me like in my previous shifts.
Incoming Operator: Jeff B
Activity Log:
Had one lockloss at 7:43 UTC, but brought it back up and into observing at 8:37. I'm still not sure what caused the lockloss.
Aside from that it is a quiet environment and everything seems to be humming along.
Lockloss at 07:43 UTC.
No idea what may have caused it yet. There was an ITMX saturation, control loops looked normal, no seismic activity, all the monitors showed normal operation.
Here's some plots.
I think it's possible that we're closer to the Newtonian gravitational noise limit than I had thought. This is on the list of "things we knew were coming, but are perhaps here sooner than I thought they would be".
The punch line is that we may be limited by Newtonian noise between 16-20 Hz. Not a wide band, but reasonably consistent with the expectations from papers such as P1200017.
In the attached plot, the blue trace is the calibrated DARM spectrum (CAL-DELTAL_EXTERNAL_DQ) that we show on the wall, taken yesterday. The green trace is my estimate of the Newtonian noise.
For the Newtonian noise, I have taken the Z-axis STS-2 seismometer data from the sensors on the ground near each test mass. (There is one seismometer at each end station, and one in the vertex near the ITMs - I use the same seismometer data for each ITM). The seismometers are in velocity units (I believe Jim said it's nm/s), so I pwelch to get velocity/rtHz, then apply the calibration zpk([],0, 1.6e-10) to get to meters/rtHz. I then translate to acceleration due to Newtonian noise using eq 1 from T1100237. Finaly, I add the 4 acceleration contributions (one from each test mass) incoherently and get to displacement by dividing the spectrum by (2*pi*f)^2.
The Newtonian noise is touching the DARM spectrum between about 16 - 20 Hz. We're within about an order of magnitude in the band 10 - 30 Hz. Evan will shortly re-run his noise budget code using this "measured" Newtonian noise to see if it helps explain some of the discrepancy between the measured and expected DARM spectra (this spectra is higher than the GWINC curve that is currently used in the noise budget).
Notably, this estimate of seismically-induced Newtonian noise is somewhat larger than what we've quoted in P1200017 and T1100237. If I use only the ETMY spectrum as an estimate for all 4 test masses, I get an answer more consistent with our past estimates. However, using the actual seismic signals from each test mass, I'm getting this slightly higher estimate.
The script to generate this plot is attached, as is the exported-from-DTT text file of the calibrated DARM spectrum.
Adding SEI tag, so people see it.
Is the STS signal calibrated correctly above 30 Hz or are you just assuming its a flat velocity sensor?
If its really close, you should be able to add the seismic data streams with the right signs and then take the coherence between this pseudo-channel and DARM and see something more than we expect by just the seismic model estimates.
Hmmm, good point Rana. I should have thought of that - it looks like the STS calibration doesn't compensate for the roll-off, so I'll put that in, and redo the traces.
Jenne, The estimate you're getting in the 15-20 Hz region is an order of magnitude or more higher than the estimate made by Jan Harms for L1, found in T1500284.
Can you post the ground noise spectra you are using so we can compare with what Jan used for L1?
The originally posted NN estimate spectra is totally wrong. I forgot to take the sqrt of the seismic spectra after pwelching, before calibrating to meters.
This corrected plot is much more consistent with Jan's estimates from T1500284.
EDIT, 3:15pm: Calibration was missing a factor of 2*pi. Plot has been updated.
Great. I like consistent results. Another remark; seismic displacement measured at a test mass has vanishing correlation with its NN. This is true at least for seismic surface fields. So if you want to proceed with correlation measurements, then the pseudo-channel needs to be constructed from an array of seismometers, with non of these seismometers being located at the test mass.
Here I include a version of the Newtonian noise estimate plot, with the GWINC estimate of aLIGO's sensitivity, in addition to the current LHO sensitivity.
The trace "GWINC with NN term" is just the regular output of Gwinc, assuming no Newtonian noise cancellation. The trace "GWINC no NN term" is all terms in gwinc except for the Newtonian noise. In particular, recall that the Gwinc NN term is not identical to the NN estimate I plot here.
The point here is to show that, although at our current sensitivity we are not limited by Newtonian noise, if we can eliminate the LSC and ASC control noise terms from our latest noise budget (aLog 21162), we likely will be.
EDIT: a further version of this plot now includes the GWINC NN curve.
When you compare "H1 SNSW EFFECTIVE RANGE (MPC) (TSeries)" data in DMT SenseMonitor_CAL_H1 with its copy in EPICS (H1:CDS-SENSEMON_CAL_SNSW_EFFECTIVE_RANGE_MPC), you will find that the EPICS data is "delayed" from the DMT data by about 109 seconds (109.375 sec in this example, I don't know if it varies with time significantly).
In the attached, vertical lines are minute markers where GPS second is divisible by 60. Bottom is the DMT trend, top is its EPICS copy. In the second attachment you see that this results in the minute trend of this EPICS range data becoming a mixture of DMT trend from 1 minute and 2 minutes ago.
This is harmless most of the time, but if you want to see if e.g. a particular glitch caused the inspiral range to drop, you need to do either a mental math or a real math.
(Out of this 109 seconds, 60 should come from the fact that DMT takes 60 seconds of data to calculate one data point and puts the start time of this 1 min window as the time stamp. Note that this start time is always at the minute boundary where GPS second is divisible by 60. Remaining 49 seconds should be the sum of various latencies on DMT end as well as on the copying mechanism.)
The 109s delay is a little higher than expected, but not to strange. I'm not sure where DMT marks the time, as the start/mid/end of the minute it outputs.
| Start Time | Max End Time | Stage |
| 0 | 60 | Data being calculated in the DMT. |
| 60 | 90 | The DMT to EPICS IOC queries the DMT every 30s. |
| 90 | 91 |
The EDCU should sample it at 16Hz and send to the frame writter. |
The 30s sample rate of the DMT to EPICS IOC is configurable, but was chosen as a good sample rate for a data source that produces data every 60 seconds.
It should also be noted that at least at LHO we do not make an effort to coordinate the sampling time (as far as which seconds in the minute) that happen with the DMT. So the actual delay time may change if the IOC gets restarted.
EDITED TO ADD:
Also, for this channel we record the GPS time that DMT asserts is associated with each sample. That way you should be able to get the offset.
The value is available in H1:CDS-SENSMON_CAL_SNSW_EFFECTIVE_RANGE_MPC_GPS
Attached is the dark noise of REFL9Q, along with an estimate of the shot noise and a conversion of these noises into equivalent frequency noise in CARM.
The dark noise appears to be slightly below the shot noise level.
I took the TNC that goes directly into the common-mode board and put it into an SR785. Also attached is the noise with the input of the SR785 terminated.
I also have tried to estimate how this compares to the shot noise on the diode. In full lock at 24 W, we see 3.6 mW of dc light on the PD (according to the calibrated REFL_A_LF channel). Off resonance and at 2.0 W, we have 13.6 mW of dc light. So the CARM visibility is about 98%.
The shot noise ASD (in W/rtHz) and the CARM optical plant (in W/Hz) are both given in Sigg's frequency response document. With a modulation index of 0.22 rad and an incident power of 24 W, the shot noise is 9.4×10−10 W/rtHz, the CARM optical gain is 11 W/Hz, and the CARM pole is 0.36 Hz. [Edit: I was missing some HAM1 attentuation when first calculating the shot noise level. Out of lock, the amount of power on REFL A should be 24 W × 0.1 × 0.5 × 0.5 × 0.5 = 300 mW. That gives a predicted shot noise level of 7.7×10−11 W/rtHz, assuming a sideband amplitude reflectivity of 0.44. On the other hand, from the measured in-lock power we can calulate 2(hνP)1/2 = 5.2×10−11 W/rtHz for P = 3.6 mW. This includes the factor of sqrt(2) from the frequency folding but does not include the slight cyclostationary enhancement in the noise from the sidebands (although this latter effect is not enough to explain the discrepancy).] Additionally, I use Kiwamu's measurement of overall REFL9 response (4.7×106 ct/W) in order to get the conversion from optical rf beat note power into demodulated voltage (2900 V/W). These numbers are enough to convert the demodulated dark noise of REFL9Q (and the shot noise) into an equivalent frequency noise. At 1 kHz, the shot noise is about 10 nHz/rtHz; as a phase noise this is 10 prad/rtHz (which is smaller than Stefan's estimate of 80 prad/rtHz). The dark noise, meanwhile, is about 5 nHz/rtHz.
Hang, Evan
We measured the input-referred voltage noise of the summing node and common-mode boards.
According to this estimate, the CARM loop is not shot noise limited; rather, at 1 kHz the noise is about a factor of 3 in ASD above shot noise.
I looked back at the CARM sensing noise data I took (on 12 Aug) using the new gain distribution: 0 dB SNB gain, −13 dB CMB common gain, 0 dB CMB fast gain, and 107 ct/ct digital MCL gain.
[For comparison, the old CARM gain distribution was 0 dB SNB gain, −20 dB CMB common gain, 7 dB CMB fast gain, and 240 ct/ct digital MCL gain.]
☞ For those looking for a message in this alog: something about the current frequency noise budgeting doesn't hang together. The projection based on the CARM sensing noise and the measured CARM-to-DARM coupling TF suggests a CARM-induced DCPD sum noise which is higher than what can be supported by coherence measurements.
☞ Second attachment: As expected, the noise (referred to the input of the SNB) is lower; at 40 Hz, it is about 350 nV/Hz1/2. However, we are not really shot-noise (or dark-noise) limited anywhere.
☞ Third attachment: I am also including the CARM-to-DARM coupling TF from a few weeks ago. This TF was taken by injecting into the CARM excitation point and measuring the response in OMC DCPD sum, using the old CARM gain distribution. Then I referred this TF to the SNB input by multiplying by the SNB gain (0 dB), the CMB common gain (−20 dB), and the CMB common boost (40 Hz pole, 4 kHz zero, ac gain of 1).
This gives a coupling which is flat at 1.0×10−2 mA/V, transitioning to 1/f2 around 250 Hz. Or, to say it in some more meaningful units:
☞ Synthesis of the above: based on the measurements described above, at 40 Hz we expect a coupling into the DCPD sum of 350 nV/Hz1/2 × 0.4 mA/V = 1.4×10−7 mA/Hz1/2, which is very close to the overall DCPD sum noise of 3.2×10−7 mA/Hz1/2.
But what is wrong with this picture? If 1.4/3.2 = 44 % of the DCPD sum noise comes from CARM sensing noise, we should expect a coherence of 0.442 = 0.19 between the DCPD sum and the CARM error point.
☞ First attachment: The coherence between the CARM error point and the DCPD sum is <0.01 around 40 Hz. Now, it is almost certainly the case that not all of the CARM error point noise is captured by LSC-REFL_SERVO_ERR, since this channel is picked off in the middle of the CMB rather than the end. Conservatively, if we suppose that LSC-REFL_SERVO_ERR contains only dark noise and shot noise, this amounts to 180 nV/Hz1/2 of noise at 40 Hz referred to the SNB error point, or 0.72×10−7 mA/Hz1/2 referred to the DCPD sum. This would imply a coherence of 0.05 or so.
☞ What is going on here?: Four possibilities I can think of are:
☞ A word about noise budgeting: In my noise budget, there was a bug in my interpolating code for the CARM-to-DARM TF, making the projection too low below 100 Hz. With the corrected TF, the projected CARM noise is much higher and begins to explain the mystery noise from 30 to 150 Hz. However, given that the above measurements don't really hang together, this is highly speculative.
According to the CMB schematic and the vertex cable layout, the CARM error point monitor goes through some unity-gain op-amps and then directly into the ADC. So I don't think we have much chance of seeing the 180 nV/Hz1/2 of shot/dark noise above the 4 µV/Hz1/2 of the ADC.
According to the CMB schematic and the vertex cable layout, the CARM error point monitor goes a gain of 200 V/V and then directly into the ADC. So the 180 nV/Hz1/2 of shot/dark noise appears as 36 µV/Hz1/2 at the ADC. But as Daniel pointed out, this should be heavily suppressed by the loop. For comparison, the ADC's voltage noise is 4 µV/Hz1/2.
For the sake of curiosity, I'm attaching the latest noise budget with the corrected CARM-to-DARM coupling TF. However, I note again that this level of frequency noise coupling is not supported by the required amount of coherence in any of our digitally acquired channels. Additionally, this level of frequency noise coupling is not seen at Livingston, although they've done a better job of TCS tuning than we have. I would not be surprised to find out that this coupling is somehow an overestimate.
