The PMC is losing power.
I'm just now realizing that the PMC has also not been locked since noon today, and doesn't seem to be responding to anything right now.
wtf is going on here?
- The PBS alignment increased the transmitted power
- The first faraday and the PMC EOM were realigned.
- The transmission of the PMC increased from ~5.4V to ~6.5V.
Thus we need to pay attention to the incident beam power on to the MC
so that it does not exceed the power of 20-40mW.
Kevin will give us the detail of the work.
I looked at PMCR camera on the MC1 tv, and tweaked up the beam going into the PMC - it only needed a little bit of pitch.
Yuta and I measured the MC spots, determined (consistent with my measurements this morning) that they were only off in yaw. We touched the 2nd steering mirror in the zigzag on the PSL table in yaw a small amount (top of knob away from me), realigned the MC, and things were good. The plot is zoomed in to show only measurements taken today. 2 in the morning, before anything in the IFO room was touched. 1 this afternoon after tweaking PMC. 1st attempt at PSL beam tweaking was successful, 2nd measurement confirms it wasn't a fluke.
The PMC power is seems to be on the rise, ( MOPA_AMPMON is dropping ?) but I do not think it is real. We have Santa Anna wind condition, when the relative humidity drops and ......
There is an other funky think. The room temp became rock solid. The PSL HEPAs running at 20% and IFO-room ACs are also in normal operational mode.
Rana showed up and diagnosed the problem as a railed FSS SLOW output. The SLOW Monitor about was showing ~6V, which is apparently a bad mode-hoppy place for the NPRO. Reducing the SLOW output brought things back into a good range which allowed the PMC to lock again.
In attempting to diagnose the problem I noticed that there is -100 mV DC coming out of the PMC RFPD RF output. This is not good, probably indicating a problem, and was what I thought was the PMC lock issue for a while. Need to look at the PMC RFPD RF output.
Jenne, Den, Rana
The PMC transmission has been varying a lot and the MC seems unstable. Superstitious people might blame this on the El-nino or the alignment with Sagitarius, but we are ostensibly scientists.
WE found that the PMC EPICS values had not been toggled since the reboot and so the RF phase and Amplitude were totally wrong (we should replace this with a fixed oscillator box as we did with FSS).
Also, the NPRO SLOW slider was at -2 V which made the mode going into the PMC funny (although the mode was OK this morning before I started playing with the PMC sliders).
Before adjustment, there was a strong correlation between the seismic motions and the PMC reflection. This means that the PMC gain was low and it couldn't stay locked. Now, after fixing the RF and upping the gain slider it looks more stable. Let's watch it for a few days to see if there's an improvement in the trends.
The 10-minute trend of the lat 400 days shows that nothing has changed much this year; its been equally bad for a long while.
PMC transmission is oscillating in the range 0.5 - 0.85. PMC PZT voltage is 1-2 V.
FSS slow controls was -2.5 V. I adjusted it to 0 and PMC stabilized. PMC PZT voltage is 128, transmission is 0.845.
But most probably, slow control will drift again.
After relocking the PMC at a good voltage, Steve and I re-aligned the beam into the PMC by walking the last two steering mirrors. After maximizing the power, we also aligned the reflected beam by maximizing the PMC_REFL_DC with the unlocked beam.
Transmission is back to 0.84 V. We need Valera mode matching maintenance to get higher I guess. Maybe we can get a little toaster to keep the PMC PZT more in the middle of its range?
PMC got unlocked at ~4am. I re-locked it. Also tweaked the input pointing into the cavity. The misalignment was mostly in pitch.
There was also a loud buzzing in the control room due to the audio cable being improperly seated in the mixer. I re-seated it.
I found the PMC unlocked this morning. It was re-locked using the usual procedure. I feel like this has been happening more frequently in the last month than before. In the past, the cause seems to have been the PZT voltage drifting too close to one of the rails - however, in this case, it looks like an IMC unlock event is what triggered the PMC lockloss (admittedly the PZT voltage was somewhat close to the rail). It would be good if someone can re-connect the PMC Transmission photodiode, it was a useful diagnostic channel we had working fine before the ringdowns started.
I also tweaked the input pointing into the PMC and ran the WFS DC offset relief script.
The PMC servo railed and so I re-locked it at ~half range. I've been noticing that the diurnal drift of the PZT control voltage has been larger than usual - not sure if it's entirely correlated with temperature on the PSL table. Anyway the cavity is locked again so all is good.
The PMC has been unlocked since September 11 sometime (summary pages are flaky again). I re-locked it just now. I didn't mess with the HEPA settings for now as I'm not using the IFO at the moment, so everything should be running in the configuration reported here. The particulate count numbers (both 0.3um and 0.5um) reported is ~x5-8 of what was reported on Thursday, September 10, after the HEPA filters were turned on. We don't have logging of this information in any automated way so it's hard to correlate things with the conditions in Pasadena. We also don't have a working gauge of the pressure of the vacuum envelope.
The RGA scanning was NOT enabled for whatever reason after the vacuum work. I re-enabled it, and opened VM1 to expose the RGA to the main volume. The unit may still be warming up but this initial scan doesn't look completely crazy compared to the reference trace which is supposedly from a normal time based on my elog scanning (the timestamp is inherited from the c0rga machine whose clock is a bit off).
Update 1500: I checked the particle count on the PSL table and it barely registers on the unit (between 0-20 between multiple trials) so I don't know if we need a better particle coutner or if there is negligible danger of damage to optics due to particulate matter.
Tonight I noticed that the drop in PMC transmission was ~1V, more than the usual of ~0.5V from the daily drift.
While re-aligning on the table, I noticed that the misalignment was not from either of the steering mirrors; i.e. I has to walk them both to get the alignment back. This implies that the misalignment is generated far upstream. Maybe the the laser itself is moving. We need some updates from Steve's laser misalignment tracker.
I have realigned the steering mirrors for PMC because the transmitted light had been at ~ 0.741
After the alignment it went back to ~ 0.850.
I realigned the steering mirrors for the PMC. The trans value went up from 0.79 to 0.83.
The misalignment was largely in the pitch direction.
A few hours ago I tweaked up the alignment to the PMC. It was really bad in pitch, and the transmission was down to about 0.711.
PMC realigned again... The transmission was down to 0.70, and the MC was having a hard time trying to autolock.
I realigned the incident beam to PMC at 23:30. The transmitted light went up from 0.78 to 0.83.
Do we have PSL pos and ang QPD trends? We should start watching them, because the PMC drifted back down to 0.76 transmission, ~3.5 days after Kiwamu realigned it (his elog is from last Thurs). Not so awesome.
I walked through the control room just now and found both PMC and MC unlocked. They're both locked now, but with PMC transmission 0.76, MC transmission ~24,500.
I have realigned the beam pointing to PMC. The transmitted light increased from 0.74 to 0.83.
The misalignment was mainly in pitch.
I realigned the input pointing into the PMC this morning. Usually, the way I do this is to minimize any discernible mode structure in the PMC reflection CCD image. Today, I noticed that making the DC reflection go down also makes the DC transmission go down. Possibilities:
Also I decreased the HEPA level down to 20 % for the night time locking.
While looking at the PMC REFL beam for the AOM diffracted beam, we noticed that although only one beam exists between the PMC and the first steering mirror, there are two afterwards and they both go to the PMC REFL RFPD!!! This is madness. We only want one beam on our PDH diode.
The reason that we have two beams is that that first steering mirrors is actually a (W1-PW-1025-UV-1064-45P) non-wedged window with an AR coating on only one side. So two beams come out of it. There is a terrible and floppy and illegal anodized aluminum dump close to this beam which *someone* probably intended to use as a "scraper" to get rid of one of the beams.
Black anodized aluminum is a horrible beam dump material at 1064 - its about as grey as Steve's chair. And its so soft that it scatters light back into the PMC and makes more acoustic noise. And it is mounted so poorly (only one screw) that it can easily be bumped and twist and miss the beam. Punchline: only use anodized aluminum dumps for stray light around cameras or for HeNe for OL. Its NOT allowed anywhere where we care about interferometry of NIR beams.
It was also set to dump the dimmer beam. On Monday, we should order ~5 W1 and get them with a wedge of 1-2 deg. Then we use a black glass dump for the dim beam and orient the bright one to hit the REFL camera and the PMC REFL PD.
For the weekend, I have adjusted the crappy grey aluminum flapper to catch the bright beam so that the PMC REFL image no longer shows the interference fringe of two beams. Lets see how the PMC drifts over the next 3 days.
The PMC was locked on an LG 10 mode (or something like it), for at least the last 8 hours. I relocked it on the regular 00 mode, and it's fine now.
Also, in CDS news, I did an mxstream restart (the RCG upgrade is supposed to make this not an issue anymore...), and did a "diag reset" afterwards, and all of the IPC errors except for one in the LSC model have gone away (OAF is still not running....on my to-do list, but not super high priority).
The PMC has been unlocked for ~23 hours. FSS slow was at ~-1.5 V. I zeroed it, and relocked the PMC, transmission is ~0.81V. MC with WFS came back fine.
PMC has been unlocked for ~4hrs, not sure why. It's servo gain was down at -10dB...
Relocked with transmission of .76V, MC locks fine with WFS, transmission of 15.5k.
I came in and PMC transmission was at 0.5V, and ETMX was swinging around a lot, (LSC mode was on).
Turning off oplevs let ETMX calm down. I realigned the PMC to 0.82V.
MC wouldn't relock, it looked misaligned in pitch and yaw on MC camera.
I've touched the alignment, and gotten the reflection below 0.5, but it unlocks periodically, spot positions aren't great, and turning on WFS throws it out of alignment. ughhhhh
PMC was locked in a bad state. FSS slow actuator adjust was at ~ -0.7 and PZT voltage at ~45.
So I set these right by moving the appropriate sliders and relocked it. FSS slow actuator adjust brought back to zero and PZT voltage ~115. PMC trans after relock is 0.789.
Found it locked on TEM01 mode.
Sweets in the fridge for non-PhD holders, courtesy of the highest levels of Caltech.
The PMC runs out of range sometimes due to the daily temperature swing. The voltage swings up after sunset and then starts to swing down before sunrise. So when you relock the PMC at the beginning of the locking night, the mnemonic from the PMC is:
Sun Go Low, Lock Me Voltage Low.
Found that the PMC gain has been set to 5.3 dB instead of 10 dB since 9 AM this morning, with no elog entry.
I also re-aligned the beam into the PMC to minimize the reflection. It was almost all in pitch.
I moved stuff on the PSL table to accommodate the PMC ringdown setup.
I used the beam that leaks from the steering mirror at the PMC transmission that was dumped to a razor blade dump. I installed a Y1 to steer the beam to the ringdown PD. Power in the beam 75mW.
Results are in here elog
I used the beam that leaks from the steering mirror at the PMC transmission that was dumped to a razor blade dump. I installed a Y1 to steer the beam to the ringdown PD. Power in the beam 75mW.
I am guessing that 75 mW will burn / destroy any Thorlabs PD. I hope that mW is supposed to be uW.
It was ~7.5mW and measured ~2V at the PD output (given its range 0-5V ) on the oscilloscope . So PD is safe !
The PMC servo error (MIX OUT MON on the panel) and actuation (HV OUT MON) have been calibrated using the swept cavity.
Error signal slope in round-trip displacement: 2.93e9 +/- 0.05e9 [V/m]
HV OUT calibration (round-trip displacement): 5.36e-7 +/- 0.17e-7 [m/V]
PZT calibration (round-trip displacement): 10.8 +/- 0.3 [nm/V] => corresponds to ~2.5 fringes for 0~250V full range => not crazy
The transmission level: 0.743V (on the PMC MEDM screen)
LO level: ~13dBm (after 3dB attenuation)
Phase setting: 5.7
PMC Servo gain: 7dB during the measurement (nominal 3dB)
- Chose PMC actuation "BLANK" to disable servo
- Connect DS345 function generator to EXT DC input on the panel
- Monitor "MIX OUT MON" and "HV OUT MON" with an oscilloscope
- Inject a triangular wave with ~1Vpp@1 or 2Hz with appropriate offset to see the cavity resonance at about the middle of the sweep.
The frequency of the sweep was decided considering the LPF corner freq formed by the output impedance and the capacitance of the PZT. (i.e. 11.3Hz, see next entry)
- 4 sweep was taken (one 2Hz seep, three 1Hz sweep)
- The example of the sweep is shown in the attachment.
- The input triangular wave and the PDH slopes were fitted by linear lines.
- Spacing between the sideband zero crossing corresponds to twice of the modulation frequency (2x35.5MHz = 71MHz)
- The error signal slope was calibrated as V/MHz
- FSR of the PMC is given by google https://www.google.com/search?q=LIGO+pmc.m
=> Cavity round trip length is 0.4095m, FSR is 732.2MHz
- Convert frequency into round-trip displacement
- Convert HV OUT MON signal into displacement in the same way.
- The voltage applied to the PZT element is obtained considering the ratio of 49.6 between the actual HV and the HV OUT MON voltage.
We have decided to keep better track (using new-fangled digital "computers") of our modifications to electronics boards.
The idea will be to create a new DCC document for every electronics board (when we pull a board and modify it, it should receive this treatment) that we have, and that document will become a history of the board's life. Version 1 will be a copy of the original drawing. Version 2 should be a modified version of that drawing with the current situation. All future versions should be modified from the most recent version, to reflect any changes. Notes for each updated version should include an elog reference to the work, so that we know why we did things, and have a place to find photos of the actual modifications. Elogs should also include a link to the DCC version. DCC titles should include the phrase "40m Revisions" for ease of searching.
Patient Zero for this new system will be the PMC servo card. The DCC number is D1400221. As of this moment, this just has the V1 original drawing with no modifications.
This has been included in the 40m's DCC document tree that Jamie started back in November 2012.
To avoid driving the PA85 without the HV rails connected, I removed R23. This was re-installed after my characterization.
Since we do the demodulation of the PMC PDH signal off this servo board, the I/F mixer output is connected to the "FP1test" front panel LEMO input.
Using some Pomona mini-grabbers, I measured the electronic TFs between various points on the circuit. There were no unexpected features, the TFs all have the expected shape as per the annotations on the DCC schematic. I did not measure down to 0.1 Hz to confirm the low frequency pole implemented by U6, and I also didn't measure the RF low pass filter at the input stage (expected corner frequency is 1 MHz).
After replacing the IC, I measured the transfer function between TP1 and TP2 for various values of the control voltage applied to pin 4A on the P1 connector, varying between +/- 5 V DC.
PZT Capacitance measurement
I confirmed that the PZT capacitance is 225 nF. The measurement was made using an LCR meter connected to the BNC cable delivering the HV to the PZT, at the 1X1 rack end.
After re-soldering R23, I put the board back into its Eurocrate, and was able to lock the PMC. For subsequent measurements, the PSL shutter was closed.
The PDH discriminant of the PMC servo was measured to be ~0.064 GV/m. This is ~50 times lower than what is reported here. Perhaps this is a signature of the infamous ERA decay, needs more investigation.
The light level hasn't changed by a factor of 50, leading me to suspect the modulation depth. Recall that the demodulation of the PMC is now done off the servo board using a minicircuits mixer (hence, the "C1:PSL-PMC_LODET" channel isn't a reliable readback of the LO signal strength over time). Although there is a C1:PSL-PMC_MODET channel which looks like it comes from the crystal reference card, and so should still work - this, however, shows no degradation over 1 year.
Somebody had removed the BLP-1.9 that I installed at the I/F output of the mixer to remove the sum frequency component in the demodulated signal, I reinstalled this. I find that there are oscillations in the error signal if the PMC servo gain is increased above 14.5 on the MEDM slider.
PMC follow up measurements have been done. The servo circuit was reviewed.
Now the PMC, IMC, X/Y arms are locked and aligned waiting for the IFO work although I still think something is moving (ITMX?)
as the FPMI fringe is quite fast.
The result of the precise inspection for the PMC servo board for the 40m was done.
The record, including the photo of the board, can be found at https://dcc.ligo.org/D1400221-v2
- I found some ceramic 1uF caps are used in the signal path. They have been replaced with film caps by WIMA.
- In later measurements with the openloop TF measurement, it was found that the notch frequency (14.6kHz) was off from the a sharp PZT resonance at 12.2kHz.
I replaced the combined caps of 1220pF to 1742pF. This resulted nice agreement of the notch freq with the PZT resonant freq.
Past related elogs:
SRA-3MH mixer installed in 2009: http://nodus.ligo.caltech.edu:8080/40m/1502
R20 increased for more LO Mon gain: http://nodus.ligo.caltech.edu:8080/40m/10172
I'm still analyzing the open loop TF data. Here I report some nominal settings of the PMC servo
Nominal phase setting: 5.7
Nominal gain setting: 3dB
After the tuning of the notch frequency, I thought I could increase the gain from 5dB to 9dB.
However, after several hours of the modification, the PMC servo gradually started to have oscillation.
This seemed to be mitigated by reducing the gain down to 4dB. This may mean that the notch freq got drifted away
due to themperature rise in the module. PA85 produce significant amount of heat.
(The notch frequency did not change. Just the 22kHz peak was causing the oscillation.)
While I have the board out, I'll try and do a thorough investigation of TFs and noise of the various stages. There is no light into the IFO until this is done.
I pulled the board out at 345pm after dialling down all the HV supplies in 1X1. I will reinstall it after running some tests.
The PMC servo was re-installed at ~345pm. HV supplies were re-energized to their nominal values. I will update the results of the investigation shortly. The new nominal PMC servo gain is +9dB.