(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)!
We can hear saturations on the quads during CARM offset reduction and when powering up, but I suppose that's the price we pay for the improved noise performance. [See attachment—blue is from yesterday (coils in high-range), red is from today (coils low range). I can't really claim that the improvements at 70+ Hz are from the coil switching, though.]
We would like to acquire with high range and then switch to low noise at some point during the lock, but the transients unlock the interferometer most of the time. Jeff suggests that we commission the digital switching delays. Perhaps that can be done parasitically with calibration activities.
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.
Calibration Measurements:
- Kiwamu, IFO down for calibrations, 16:05UTC - 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, 16:07UTC - done
- Hugh to EX and EY, HEPI, 16:07UTC- done
- JeffK, ETMY, measuring coil drivers, 16:15UTC
- Sudarshan, PEM channel check in LVEA, 16:20UTC- done
- TJ EX BRS reset - 16:54UTC- done
- Kyle, near EY (Y28) to gather stuff - done
- Dave, EX, drawing updates - 19:10UTC- done
- Kyle, near EY (Y28) to gather stuff, 19:54UTC- 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.
Small correction: SRC1Y uses the following input matrix (alog 20699): AS_A_RF36_I_YAW to SRC1_Y : -3 AS_B_RF36_I_YAW to SRC1_Y : 1
Following up to the problem (insufficient whitening) reported in alog 20700, new dewhitening filters are implemented in the following DEALTAL_CTRL channels:
H1:CAL-CS_DARM_DELTAL_CTRL_M0/L1/L2/L3_WHITEN: Original -- (zpk([1, 1, 1], [500,500,500],1,"n")
Changed to (zpk([0.1,0.1,0.1,0.1], [100,100,100,100],1,"n")
H1:CAL-CS_DARM_DELTAL_CTRL_SUM_WHITEN: Original --(zpk([1, 1, 1,1,1], [100,100,500,500,500],1,"n")
Changed to (zpk([0.1,0.1,0.1,0.1], [100,100,100,100],1,"n")
The first attached plot shows DARM CTRL signal with original filter in dotted lines and the new filter in solid lines.
The second plot shows the effect of different filter combinations on DARM_CTRL signal. This measurement gave us an intuition on what filter to use eventually.
- Duty Cycle: 54%
- range: 75 - 85 Mpc
- PRM M3 LL coil driver caused noise in 10-60 Hz range on Friday, may have been responsible for some loud glitches
- Also on Friday there were some strange lines in the strain spectrogram at around 10Hz
- loud glitches that cause brief, large drop in range that we saw in ER7 continue; the rate is improved
Please note that the range on the summary pages is not correct. The range displayed in the control room has been hovering around 60-65 Mpc, and this is much more realistic, although not yet blessed by the calibration group.
JeffreyK, Kiwamu, Darkhan
Overview
A DARM OLG TF model and its parts, sensing and actuation functions, are used for calculating the interferometer strain, h(t), and estimation of uncertainty in reported h(t).
On last Thursday we put together a DARM OLGTF Matlab model for ER8/O1 and compared it to a DARM OLGTF measurement taken on Aug 17, 2015. This model is mainly based on a similar model for ER7 (LHO alog 18769). Currently the model agrees with the measurement to only about +/-10% in magnitude and +/- 5 deg up to 200 Hz. So there's still work need to be done, probably changing parameter file needs some fine tuning of possibly following parameters: optical gain, CC pole frequency, ESD zeros and poles, ESD gain.
Details
Please, see a summary of things to be aware of when using this model (mostly listed differences from ER7 model):
[ol, par] = H1DARMmodel_ER8('par_file');
freq = 10 : 1 : 100;
G = par.G.getFreqResp_total(freq);
A = par.A.getFreqResp_total(freq); % total actuation function
% frequency responses of actuation stages can be obtained similarly
A_tst = par.A.getFreqResp_TST(freq);
% frequency responses of C with and without CC pole
C = par.C.getFreqResp_total(freq);
C_res = par.C.getFreqResp_noCavPole(freq);
We still need to take more DARM OLGTF and PCAL to DARM TF measurements and compare them to better estimate DARM model parameters.
The model was uploaded into calibration SVN (r1095):
CalSVN/aligocalibration/trunk/Runs/ER8/H1/Scripts/H1DARMOLGTFmodel_ER8.m
The parameter file associated with measurement taken on Aug 17 is in the same directory:
CalSVN/aligocalibration/trunk/Runs/ER8/H1/Scripts/DARMOLGTFs/H1DARMparams_1123894143.m
I believe that these scripts are in a reasonable shape to try it with LLO DARM parameters.
The fluid levels are essentially unchanged since the end of July. The EndX is down <1/16" but I'll wait for more data to claim a trend from a leaky Accumulator. No further HEPI Maintenance needed tomorrow.
BRS software crashed at the end of last week. I got a chance to head to EX and restart the code from the desktop in the rack room.
I kept the damper OFF for now to see whether or not it is rung up.
J. Kissel, K. Izumi, S. Karki, D. Tuyenbayev, R. Savage I attach a picture of the whiteboard where we've sketched out our plan for the week. We've gone through T1500443, taken off items that we've already managed to capture before this week, and prioritized the remaining tasks accordingly. Stay tuned for daily updates on progress.
J. Kissel, K. Izumi At 16:02 UTC, we've taken the IFO down to begin calibration measurements. On today's docket: - Actuation function frequency dependence checks - UIM, PUM Coil Driver TFs - ESD LVLN Driver TFs - Sensing function frequency dependence checks - OMC DCPD AA Chassis - OMC DCPD PreAmp (with single bounce IFO)
Sheila, Evan
We looked again at the situation with the 45 MHz REFL WFSs, which are used as sensors for the PR3 ASC loop. In the end, we didn't implement any changes to the sensors or the associated loops.
We were motivated by the following:
We tried the following:
After that, we couldn't get to full power because of an oscillation that showed up in dHard pitch when going to 20+ W. (We've seen this before, and it seems to be distinct from the angular instability mentioned above.) To get around this, we had to slightly beef up the resonant gain that gets turned on in dHard pitch when the power is increased.
Also, there were some small maintenance tasks that we did:
Two of the chaanges that we made last night we kept.
With the new phasing for refl 45, it was no longer a good sensor to use in DRMI, so we changed PRC2 in this configuration to using the sum of refl A and B 9I. This is in the DRMI guardian and works fine, so we've left it there.
We left the DC coupled OpLev off, we think the cage servo will have less drift.
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:
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.
* What is the reasoning behind the updated suspension thermal noise plot?
* Its weird that cHard doesn't show up. At LLO, cHard is the dominant noise from 10-15 Hz. Its coupling is 10x less than dHard, but its sensing noise is a lot worse.
I remade this plot for a more recent spectrum. This includes the new EOM driver, a second stage of whitening, and dc-lowpassing on the ISS outer loop PDs.
This time I also included some displacement noises; namely, the couplings from the PRCL, MICH, and SRCL controls. Somewhat surprising is that the PRCL control noise seems to be close to the total DCPD noise from 10 to 20 Hz. [I vaguely recall that the Wipfian noise budget predicted an unexpectedly high PRCL coupling at one point, but I cannot find an alog entry supporting this.]
Here is the above plot referred to test mass displacement, along with some of our usual anticipated displacement noises. Evidently the budgeting doesn't really add up below 100 Hz, but there are still some more displacement noises that need to be added (ASC, gas, BS DAC, etc.).
Since we weren't actually in the lowest-noise quad PUM state for this measurement, the DAC noise from the PUM is higher than what is shown in the plot above.
If the updated buget (attached) is right, this means that actually there are low-frequency gains to be had from 20 to 70 Hz. There is still evidently some excess from 50 to 200 Hz.
Here is a budget for a more recent lock, with the PUM drivers in the low-noise state. The control noise couplings (PRCL, MICH, SRCL, dHard) were all remeasured for this lock configuration.
As for other ASC loops, there is some contribution from the BS loops around 30 Hz (not included in this budget). I have also looked at cHard, but I have to drive more than 100 times above the quiescient control noise in order to even begin to see anything in the DARM spectrum, so these loops do not seem to contribute in a significant way.
Also included is a plot of sensing noises (and some displacement noises from LSC) in the OMC DCPDs, along with the sum/null residual. At high frequencies, the residual seems to approach the projected 45 MHz oscillator noise (except for the high-frequency excess, which we've seen before seems to be coherent with REFL9).
Evidently there is a bit of explaining to do in the bucket...
Some corrections/modifications/additions to the above:
Of course, the budgeted noises don't at all add up from 20 Hz to 200 Hz, so we are missing something big. Next we want to look at upconversion and jitter noises, as well as control noise from other ASC loops.
Using the calibrated DRMI channels created and described by Kiwamu in entry 18742, I grabbed data from the lock of August 3, 2015, starting at 04:20:00 UTC. The attached 4 page PDF shows spectra of the open loop and residual displacement noise for SRCL, MICH and PRCL. The 4th page shows the coherence of SRCL with the other 2 degrees of freedom.
Degree of freedom | Residual rms | Shot noise level |
---|---|---|
SRCL | 8 pm | 1.3 x 10-15 m/rtHz |
MICH | 3 pm | 1.5 x 10-16 m/rtHz |
PRCL | 0.8 pm | 4 x 10-17 m/rtHz |
The SRCL spectra has a curious shape: it comes down quickly with frequency to 10 Hz, then is fairly flat from 10 Hz to 50 Hz, then falls by a factor of 5 or so to the (presumed) shot noise level that is reached above 100 Hz. What is this noise shelf between 10 Hz and 80 Hz? That is exactly the region where the SRCL noise coupling to DARM is troublesome. Our usual approach is to send a SRCL correction path to DARM to reduce the coupling, but this spectrum shows that there should also be some gain to be had by reducing this noise shelf.
The last page of the PDF shows the coherence between SRCL and MICH & PRCL, and it indicates that the SRCL noise shelf could be coupling from PRCL noise -- the coherence is fairly high in this band, though not unity. This suggests that the DRMI signals could use some of the demodulator phase and input matrix tuning that Rana has recently done on L1, reported in LLO log entry 19540.
To complete this log entry, it would be useful if someone at LHO could add the open loop transfer functions for each loop (models), and other pertinent info such as DC photocurrents for these detectors and the input matrix coefficients.
The shelf appears to be gain peaking in SRCL. We have an 80 LPF to get rid of SRCL control noise in the bucket, but it makes the control noise from 30 to 60 Hz a bit worse.
I had the filter off between 2015-08-23 00:36:00 Z and 00:39:00 Z. The attachment shows the error and control signals with filter off (dashed) versus filter on (solid).
Evan, is the shelf in Peter's open loop spectrum there because of OLTF model without LPF? Otherwise, we still need to investigate.
We observed broadband coherence of OMC_DC_SUM with ASC_AS_C_LF_SUM and ASC_A_RF36_PIT. We made some numbers and plots, using the 64kHz version of the channels. First the measurements we made on OCXO oscillator: - ASC_AS_C sees a RIN of about 5e-7/rtHz above 100Hz (either from H1:ASC-AS_C_SUM_OUT_DQ or from H1:IOP-ASC0_MADC6_TP_CH11). The same is true for its segment 1. - The calculated shot noise RIN at 20mA (quantum efficiency 0.87) detected is 4.0e-9/rtHz. - The 4.0e-9/rtHz agrees with DCPD_NULL_OUT_DQ's prediction (8.0e-8 mA/rtHz/20mA). - DCPD_SUM_OUT_DQ sees a slightly elevated RIN of 4.6e-9/rtHz (9.2e-8 mA/rtHz/20mA). - The RIN in DCPDA (H1:IOP-LSC0_MADC0_TP_CH12, corrected for the whitening) is about 5.9e-8 mA/rtHz, or RIN = 5.9e-9/rtHz at 20mA/2diodes (~15pm DARM offset)... - ...or about 3.3e-8 mA/rtHz or 1.2e-8/rtHz at 5.7mA/2diodes (~8pm DARM offset). - ASC-AS_C_SEG1 (H1:IOP-ASC0_MADC6_TP_CH11) and OMC-DCPD_A (H1:IOP-LSC0_MADC0_TP_CH12) shows a coherence of 0.053 at 20mA, suggesting a white noise floor a factor of 0.23 below shot noise. - At 5.7mA the same coherence is about 0.13, i.e. the white noise floor is a factor of 0.39 below shot noise. - These two measurements are in plot 1. - Taking the last two statements together, we predict a coherent noise of - 5.9e-8 mA/rtHz *0.23 = 1.4e-8 mA/rtHz at 20mA/2diodes (~15pm DARM offset) (RIN of coherent noise = 1.4e-9/rtHz) - The pure shot noise part is thus 5.7e-8 mA/rtHz - 3.3e-8 mA/rtHz *0.39 = 1.3e-8 mA/rtHz at 5.7mA/2diodes (~8pm DARM offset) (RIN of coherent noise = 4.5e-9/rtHz) - The pure shot noise part is thus 3.0e-8 mA/rtHz. - AS_C calibration: - 200V/W (see alog 15431) - quantum efficiency 0.8 (see alog 15431) - 0.25% of the HAM 6 light (see alog 15431) - We have 39200cts in the AS_C_SUM. Thus we have - 39200cts / (1638.4cts/V) * 10^(-36/40) (whitening) / (200V/W) = 1.89mW and AS_C. (shot noi - 1.89mW/0.025 = 76mW entering HAM6. I.e. we have slightly more sideband power than carrier power (Carrier: 27mW in OMC transmission). - Shot noise level on AS_C_SUM is at 2.0e-8 mA/rtHz, corresponding to a RIN of 1.6e-8/rtHz. I.e. the coherent noise seen at 5e-7/rtHz is high above the shot noise. Dark noise TBD. - The light entering HAM 6 has a white noise of 5e-7/rtHz*76mW = 3.8e-5 mW/rtHz Bottom line: -We have ~1.4e-8mA/rtHz, or 1.9e-8mW/rtHz of coherent white noise on each DCPD. -It corresponds to 3.8e-5mW/rtHz before the OMC, i.e. the the OMC seems to attenuate this component by 2000. -This noise stays at the same level (in mW/rtHz) for different DCPD offsets. Next, we switched back to the IFR for testing. plot 2 shows the same coherences (all at 5.7mA / 8pm DARM offset), but on the IFR. Interestingly now AS_C and AS_A_RF36 start seeing different noise below 2kHz. We convinced our selfs that the higher excess noise seen in AS_A_RF36 is indeed oscillator phase noise from the IFR - so that is clearly out of the picture once of the OCXO. (Evan will shortly log the oscillator phase noise predictions.) 64k Channel list: H1:IOP-LSC0_MADC0_TP_CH12: OMC-DCPD_A (used in plot) H1:IOP-LSC0_MADC0_TP_CH13: OMC-DCPD_B H1:IOP-LSC0_MADC1_TP_CH20: REFLAIR_A_RF9_Q H1:IOP-LSC0_MADC1_TP_CH21: REFLAIR_A_RF9_I H1:IOP-LSC0_MADC1_TP_CH22: REFLAIR_A_RF45_Q H1:IOP-LSC0_MADC1_TP_CH23: REFLAIR_A_RF45_I H1:IOP-LSC0_MADC1_TP_CH28: REFL_A_RF9_Q H1:IOP-LSC0_MADC1_TP_CH29: REFL_A_RF9_I H1:IOP-LSC0_MADC1_TP_CH30: REFL_A_RF45_Q H1:IOP-LSC0_MADC1_TP_CH31: REFL_A_RF45_I H1:IOP-ASC0_MADC4_TP_CH8: ASC-AS_A_RF36_I1 H1:IOP-ASC0_MADC4_TP_CH9: ASC-AS_A_RF36_Q1 H1:IOP-ASC0_MADC4_TP_CH10: ASC-AS_A_RF36_I2 H1:IOP-ASC0_MADC4_TP_CH11: ASC-AS_A_RF36_Q2 H1:IOP-ASC0_MADC4_TP_CH12: ASC-AS_A_RF36_I3 H1:IOP-ASC0_MADC4_TP_CH13: ASC-AS_A_RF36_Q3 (used in plot) H1:IOP-ASC0_MADC4_TP_CH14: ASC-AS_A_RF36_I4 H1:IOP-ASC0_MADC4_TP_CH15: ASC-AS_A_RF36_Q4 H1:IOP-ASC0_MADC6_TP_CH11: ASC-AS_C_SEG1 (used in plot) H1:IOP-ASC0_MADC6_TP_CH10: ASC-AS_C_SEG2 H1:IOP-ASC0_MADC6_TP_CH9: ASC-AS_C_SEG3 H1:IOP-ASC0_MADC6_TP_CH8: ASC-AS_C_SEG4
Some more estimation - this time for frequency noise: - Shot noise on the refl diodes is given by Pshot=sqrt(2*h*nu*Pr_lock) - The cavity sensing function is P_9_pk = 4*Gam9*P0 * dNu(f)/(f_p + i*f), where P0 would be the carrier power incident on the PD without the IFO. - from this we can estimate a frequency (phase) noise of about 8e-11 rad/rtHz. Gam9=0.219; %alog15874 PSL_low=2; %W Pr_nolock_low=13.7e-3; %W PSL_lock=24; Pr_lock=3.5e-3; %W IMCt=0.88; att=Pr_nolock_low/(PSL_low*IMCt); P0=PSL_lock*IMCt*att; inlockdrop=Pr_lock/(P0); Pshot=sqrt(2*h*nu*Pr_lock); dphi=Pshot/P0/4/pi/Gam9;
For reference, I ran the numbers on where we would expect the sidebands to show a resonance feature. I used the following values: RITM=1939.3m RETM=2241.54m L=3994.485m Checking accidental sideband resonances in the arm cavities: Resonance condition: fres = FSR * (q + (l+m+1)*fTM/FSR) Free Spectral Range (FSR) : 37.5258 kHz Transverse Mode Spacing (fTM): 32.4297 kHz Checking f1 sideband: q=242 l+m=0 Freq. diff. = 18.2284 kHz q=242 l+m=0 Freq. from antiresonant = 0.534516 kHz q=242 l+m=1 Freq. diff. = 14.2013 kHz q=241 l+m=1 Freq. from antiresonant = 4.56162 kHz q=241 l+m=2 Freq. diff. = 9.10514 kHz q=-242 l+m=0 Freq. diff. = 18.2284 kHz q=-243 l+m=0 Freq. from antiresonant = 0.534516 kHz q=-243 l+m=1 Freq. diff. = 13.1322 kHz q=-244 l+m=1 Freq. from antiresonant = 5.63065 kHz q=-244 l+m=2 Freq. diff. = 8.0361 kHz Checking f2 sideband: q=1212 l+m=0 Freq. diff. = 16.0903 kHz q=1212 l+m=0 Freq. from antiresonant = 2.67258 kHz q=1212 l+m=1 Freq. diff. = 16.3393 kHz q=1211 l+m=1 Freq. from antiresonant = 2.42356 kHz q=1211 l+m=2 Freq. diff. = 11.2432 kHz q=-1212 l+m=0 Freq. diff. = 16.0903 kHz q=-1213 l+m=0 Freq. from antiresonant = 2.67258 kHz q=-1213 l+m=1 Freq. diff. = 10.9942 kHz q=-1214 l+m=1 Freq. from antiresonant = 7.76872 kHz q=-1214 l+m=2 Freq. diff. = 5.89804 kHz
Evan, Matt, Lisa We did one more test for the broadband coherence noise: Common mode gain +3dB vs -3dB We see no chnge in the broadband level of the noise below 10000Hz. However, we do see an FSS gain oscillation at 7320Hz showing up in the OMC_DCPD_SUM - but not in AS_C_LF or AS_A_RF36 - in fact that coherence has adip where we get the frequency noise oscillation. This strongly suggests that our broadband noise is NOT frequency noise. Evan also took the frequency noise transfer function - a preliminary analysis here also confirms: the frequency noise should be significantly below the O(1e-8mA/rtHz) noise level we see.
Note that the higher order mode estimates above were made using a slightly wrong modulation frequency. Updated estimates for the correct modulation frequency are attached to alog 20147
- ASC-AS_C GETS 2.5% of the HAM 6 light (see alog 15431) (NOT 0.25%)
Actually AS_C gets 400ppm of the light entering HAM6 -- the OM1 mirror was swapped from 5% transmission to 800ppm transmission in early April. See alog:17738.