In addition to the BruCo scans for SRCL/MICH/PRCL error signals, the attached plot shows the coherence of the three auxiliary longitudinal error signals with the DBB jitter signals. There is some coherence, mostly below 30 Hz, but not much.
I have increased the heat by 1 stage in Zone 2B in the LVEA.
State of H1: laser is off
Summary of Weekend issues:
The weekend has not been good for the laser and I didn’t get to investigate the coupling at HAM2 more, complete the PEM injections I wanted to make, or even look through the viewport. I attach a plot from Friday’s work showing that shaking by about a factor of 10 at HAM2 produces a couple of features 3 or 4 times above the DARM noise floor. The second figure shows the results of heavy shaking.
03:35 UTC Connecting to ~100,000 channels from conlog-test-master.
23:27 UTC Disconnected and reconnected to channels.
In this case, the flow rate for head 4 clearly dropped below 0.5 lpm causing the watchdog to trip.
Corey has cancelled Ed's owl shift and the rest of mine. 23:04 UTC reset HAM2 HEPI watchdog 23:08 UTC reset HAM2 ISI watchdog 23:12 UTC MC locked. Leaving in down state for Robert. 23:19 UTC PSL tripped off. 23:20 UTC Peter to LVEA to remove PSL test equipment 23:27 UTC Peter back 23:30 UTC Peter back to LVEA 23:32 UTC Peter back 23:40 UTC reset noise eater 23:47 UTC taking power to 50W with just IMC locked for Robert. 23:53 UTC Taking power back to 2W 23:54 UTC Attempting to lock 00:23 UTC PRMI not locking. Starting initial alignment. 00:50 UTC Initial alignment done. 00:53 UTC ETMs are misaligned. Taking input power to 50W for Robert. 01:12 UTC Back to 2W. Attempting to lock. 01:28 UTC reset noise eater 01:39 UTC reset noise eater, back to CHECK_IR 01:51 UTC locked on PRMI, adjusted BS and PRM. PRMI to DRMI transition held, but signals in striptool very ratty. Lost lock on TURN_ON_BS_STAGE2. Not making it through DRMI locked. I'm suspecting the ISS is oscillating. 02:38 UTC PSL tripped off. Just when I got the ISS and FSS relocked (had to turn random knobs and reset the noise eater a number of times).
The laser tripped out again. Attached are two plots of the flow rate signals around the time of the trip.
Bear in mind that the minimum head flow rate was set to 0.5 lpm. The flow rate for head 4 had a small
excursion close to 0.5 lpm. Zooming in on the low point shows the flow rate to be above this limit.
It might be that the flow rate may have dipped below this level faster than the sampling time between
TwinCAT/OPC and EPICS.
Assuming that the flow rate in head 4 did not trip the laser out, then the problem lies with the
crystal chiller. Not sure why at this stage. One thing to try the next time is to swap where the
chiller(s) get their 3-phase power, ie interchange where the crystal chiller plugs in to where the
diode chiller plugs in and vice versa. The chiller is relatively new, so it's hard to believe that there's
something wrong with it but at this point everything points in that direction - in my opinion.
Most of the laser trips have been associated with the crystal chiller. Even with the previous two
chillers that were used. The only thing we did not change was where the crystal chiller was plugged in.
Swapping its power socket with the diode chiller might fix the problem or switch the problem over to the
diode chiller.
The "electronic" flow sensors have been removed and the flow rate values have been forced within
TwinCAT.
Should the laser trip out again, please do not bring it back.
Attached are the head flows for the past 2 hours.
state of H1: IMC was lockednow unlocked
Help: Jason, Peter
Ditails:
Should the laser trip off later on this evening, please do not attempt to bring it back. There are a couple of things that are cobbled in that I would like removed before the laser is restored.
The pre-modecleaner had some problems re-acquiring after the last laser trip. The symptoms were that one could
see resonant flashes but the servo never really grabbed. The pre-modecleaner high voltage signal instead of
looking like a ramp signal, looked like three parallel lines which is probably indicative of the high voltage
oscillating. This is also an indication that the beam is not well centred on the locking photodiode.
I re-aligned the beam both into the pre-modecleaner and onto the locking photodiode. Unlocked the DC output
was ~1V. Locked, ~0.26V. Crudely that's a visibility of 74% with the ISS off. That is consistent with the
power throughput of the pre-modecleaner as calculated from the values displayed on the MEDM screen.
In bring the FSS back up using the autolocker, I noticed that the common gain kept going between 0, 2 and
16 dB even though the autolocker status did not indicate the gain was being ramped. I assume this was guardian
doing its thing.
The ISS however seems to be exhibiting signs of one of the switches being touchy because turning the loop
on/off at times seems to have no effect. Unless, of course, the corresponding DAC channel is intermittent.
Hamlet 1.4
Peter has been in the PSL aligning, and is now in the CR attempting to restore the FSS and ISS and at this point they have not come back.
Installed the "electronic", ie dummy, flow sensors into both the power meter and front end circuits.
So the two readouts of those flow rates will be bogus for a while. Currently the front end circuit
reads 4.5 lpm and the power meter circuit reads 0.5 lpm. Even though the current sources were set
to mimic the real flow rate.
The Martel calibrator always complains that it is "OPEN LOOP". The other source didn't have
any error messages.
The minimum flow rate trip point was increased from 0.2 lpm to 0.4 lpm.
The Beckhoff terminal for the flow rates reports the following:
- an under-range and error flag for the power meter circuit
- an over-range and error flag for the front end circuit
The laser was still running under these conditions.
I decided to try force writing these variables in TwinCAT to match the previous values.
The "electronic" flow sensors are still attached however.
I had to set the bottom plot to "transfer function" and back to coherance to get the X axis to start at 121 and end at 700
Something happened early in the morning today (about 2016-10-08 12:50 UTC +- 10 min) and the transmission is only 78W as of now while the reflection is 38W or so.
It looks like the ISS diffracted power jumped up at the lockloss. I started changing the H1:PSL-ISS_REFSIGNAL to bring it back, but then trended it and saw it hadn't changed, so put it back.
More about changes in PMCsignals at lock loss: PMC Trans drops, FSS and ISS increase in power
Evan, Daniel
17:12:30 UTC Oct 7 2016:
17:16:30 UTC Oct 7 2016:
17:18:30 UTC Oct 7 2016:
17:24:30 UTC Oct 7 2016:
17:32:00 UTC Oct 7 2016:
17:34:30 UTC Oct 7 2016:
18:06:30 UTC Oct 7 2016:
Spectra attached.
Coherence (modulation on)
Using 2600 V/W for the demod gain and transimpedance, and 29 mW of dc PD power, this implies the following AM depths:
| I | Q | |
| 9 MHz | 0.95×10−4 | 2.4×10−4 |
| 45 MHz | 1.9×10−4 | 8.2×10−4 |
Using 0.22 rad and 0.28 rad for the 9 MHz and 45 MHz modulation depths, this implies the following AM/PM ratios:
| I | Q | |
| 9 MHz | 0.43×10−3 | 1.1×10−3 |
| 45 MHz | 0.67×10−3 | 2.9×10−3 |
The attachment contains a budget of the expected CARM residual. The in-loop error point is taken from the CM board control signal, as was done previously. Here I used 2600 V/W for the transimpedance and demod gain.
The other measured traces are taken from the REFL9I readback (not from the CM board), so in principle there could be some extra dark noise at the error point from the summing node board or CM board. However, based on the O1 level this is of the same order as the shot noise (so we are not missing a huge amount of extra noise in this estimate).
Attaching earlier RAM plot, this time with informative labels
Here is a time series of REFL LF during the modulation depth reductions that happen during lock acquistion.
During the 9 MHz depth reduction (from 0.22 rad to 0.11 rad), the dc power changes from 4.83(3) mW to 4.27(3) mW. That means that after the modulation depth reduction, 4.08(4) mW of the dc light is from the carrier and 0.19(2) mW of the dc light is from the 9 MHz sideband (this assumes the 45 MHz contribution is negligible).
Note that the dc level is still settling to its final value of ~3.7 mW, so it's possible that these power ratios are evolving during the lock.
