Last night we roughly adjusted the cross overs of SRM and PRM to be about 4.5 Hz, I have checked both cross overs using PRX and SRY. I adjusted the gain in FM1 of M2 lock for both suspensions, so it is still true that the gain you enter for M2 will be the cross over frequency.
Taking RGA data as the pressure in the X2 Beam Tube module increases following the closing of GV15 (removal of hydrogen pump) -> Expect increasing pressure values indicated by PT345B, PT346B, PT523B and PT524B during test period (testing done on Monday) -> Pressures indicated by these gauges aren't to exceed 5 x 10-7 torr during test period
08:22 Andres to LVEA West Bay cleanroom to collect parts
09:35 Cris to EX
12:00 Gerardo to LVEA taking photos of X-arm beam tube
13:20 Aaron pulling cables from PSL to electronics room
14:41 Gerardo to EX on tool hunt
A DB9 cable was pulled for the outer loop power stabilisation. The cable is labelled as ISS AA: 13-16. Male end in the LVEA, female end in the CDS High Bay. Aaron, Manny, Peter
We ran a set of TFs on this al-metal QUAD assembly today. The main chain looks to be free of mechanical grounding and suspension resonances look to be roughly in the corect places. The reaction chain looks to be a little more wild, so we'll investigate that chain further.
Following what I did on BS (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=13988), I configured the ITMX-ISI and ITMY-ISI in the same configuration:
ST1: TSheila everywhere, except on Z (T750mHz). A T750mHz blend helps limiting the pick up in RZ.
ST2: T750mHz everywhere. Provides isolation above 1Hz without reinjecting noise at low frequency.
On ITMY, we see some good improvement in YAW without degrading PITCH too much.
On ITMX, the degradation in PITCH is a little worse: we might want to turn on some optical lever damping loops to kill this 0.55Hz peak.
DetCharacters have requested to see plots of our loop designs for some of our platforms. I just finished new controllers for ITMX, but they are not currently installed. These are not necessarily representative, but unless smarter people (who are legion) point out where I went wrong, they are what I would like to have working everywhere.
There was some suspicion that the REFL beam is somehow clipped on LSC REFL_A diode. Yesterday I made a long scan of RM1 and RM2, separately and at the same time.
LSC-REFL_A_LF is good, ASC-REFL_B too.
I had to move RM1 and/or RM2 by a large amount to make the LSC-REFL_A_LF drop.
ASC-REFL_B is also good, though the safe range is smaller than LSC (not surprising considering the short focal length lens in front of LSC diode).
ASC_REFL_A is unhealthy.
Something is wrong with SEG4.
It seems as if SEG4 has a lower trans impedance, in that when I steer the beam to SEG4 (all power falls on that segment) we get 18000 counts, but when I do the same thing to SEG1/2/3 they rail at 32k counts.
In the attached, the beam was in SEG3 at first, and I walked the beam to SEG4, then SEG1, then SEG2, and then back to SEG3 by turning RM1.
The problem seems to be in the WFS head, not in the WFS interface board. Connected the WFS output cable from the REFL_A head to REFL_B input and the problem is still there.
For the moment I adjusted the digital gain of SEG4 such that there's no coupling from PIT and YAW motion to the SUM (new H1:ASC-REFL_A_DC_SEG4_GAIN=1.9), but this needs to be investigated further.
The second attachment shows the REFLA SUM spectrum of before (green) and after (red) of the gain adjustment when I was modulating PIT of RM1 at 3.3Hz and YAW at 5Hz. For comparison, Blue/Brown are the REFLB SUM data which show no alignment coupling.
Could be the electronics in the head or the cable (one end of the differential signal is dead?). I hope that the diode is not damaged.
Though not impossible, I don't think it's clipping because SEG4 never went larger than 19000 counts during RM1/RM2 full scan.
I checked the analog signal coming to the WFS interface chassis using a DB15 breakout board, and sure enough, there was no signal coming from one of the SEG4 differential drivers (don't remember if it was pin4 or pin12).
To check if the problem is in the cable between the rack and the chamber, we swapped the cable for WFSA and WFSB at the chamber.
Right after they were swapped, for a few minutes both WFSA and WFSB looked good and we were confused, but eventually WFSA SEG4 (which showed up in WFSB SEG4 channel because of the cable swap) got back to crappy half-signal state.
We swapped the cables back, WFSA SEG4 got back to good state for some minutes, and again after a while it went back to the bad state.
It seems to me that a crappy feedthrough is doing its own thing. The problem feedthrough is D6-1C1 on HAM1.
(However, it's not totally impossible that the feedthrough is OK but the seg4 in-vac circuit works only for a few minutes after it is powered on because of slowly developing oscillation or thermal problem or whatever.)
We know from the cable swap excersize that it's not the WFSA in-air cable.
I wiggled PRM at 4.13 Hz in PIT (attached, left) and 6Hz in YAW (right).
The DC level during the measurement was: about 80 for LSC-REFL_A_LF, about 40000 for WFS DC SUM.
The OSEM witness is supposed to be calibrated in micro-radians.
Using the above information, the PRM angle to the RIN coupling for these sensors are:
About 1 RIN/urad for LSC-REFL_A_LF, about 10 for WFSs.
model restarts logged for Wed 17/Sep/2014
2014_09_17 13:14 h1suspr2
2014_09_17 13:14 h1sussr2
2014_09_17 14:47 h1fw0
2014_09_17 18:14 h1sussrm
2014_09_17 22:27 h1fw1
unexpected restarts of h1fw[0,1]. Sus TACQ model changes.
Alexa, Rana, Sheila, Kiwamu,
We locked the DRMI tonight for the first time. It could stay locked for more than 10 minutes.
(A prep: PRMI locking with REFL signals)
Before moving onto the DRMI locking, we wanted to lock the PRMI on the sideband without using the AS detector. We first locked the PRMI with the conventional sensors i.e. REFL9_I for PRCL and ASAIR_45Q for MICH respectively. By exciting and looking at transfer coefficients, we figured out
REFL45_Q = -12.5 x ASAIR_RF45_Q for MICH readout
So, we put 1/-12.5 = -0.08 in the input matrix and this worked.
Also, the large fluctuation we saw in REFL_A_RF45 yesterday (alog 13968) was visible today as well before we transitioned to REFL_RF45_Q for MICH. We checked if this behavior is also visible in REFLAIR_A_RF45. This was actually visible in REFLAIR_RF45 as well. This incidicates the fluctuation comes from some kind of common place in the REFL path or the ASAIR_A is imposing this fluctuation in the MICH through its feedback. Once we transitioned onto REFL_A, we saw both REFL_A and REFLAIR RF45 signals suppressed. On the other hand, as expected, ASAIR then started wandering. We should check some clipping or some obvious things on the ASAIR detector tomorrow.
(DRMI lock)
We aligned the SRC by locking SRY with ASAIR_RF45. Also we adjusted the demod phase of ASAIR_B_RF90 such that the signal is maximized in in-phase. At the beginning, we adjusted the demod phase such that the PRMI carrier resonance gave negative values. This was then flipped by 180 deg after we locked the DRMI because this signal stayed at a negative value when the DRMI was locked.
To lock the DRMI, we reduced the MICH gain by a factor of 5 according to Anamaria's DRMI document, but eventually we ended up with a gain reduction of only a factor of three which resulted in repeatable locking. We did not have to change the PRCL gain from the PRMI locking gains as expected. We guessed the SRCL gain from the same document. We fiddled with the control sign and gain for an hour or so and eventually it started locking.
We coarsely adjusted the PRM and SRM M2 stages to maintain the DRMI lock for a long time. The gains are right now based on some models/guesses. So we will revisit these values tomorrrow.
(SRC hopping ?)
We are not sure what is going on, but the SRC seems to jump back and forth between two modes. It looks as if the hopping is triggered by some slow misalignment. Depending on time, it happened as frequent as once per a couple of seconds. And sometimes it did not happen for some time like 20 seconds or so. This is visible in the dark port camera and AISAIR_RF90 which went back and forth between a high and low values. The low value went to a negative number for some reason. We need to investigate this issue more to figure out what is happening.
The attached video is of the AS port durring a DRMI lock. Towards the end, there are a few of the mode hopping events that Kiwamu described in his alog.
Also attached is a screen shot of various settings with DRMI locked.
We are setting the intent bit to undisturbed, since as far as we know there aren't any sseismic transfer functions starting tonight and we are leaveing DRMI locked on the sidebands.
When activity starts in the morning, it would be good if the operator could set the intent bit (on the ops screen) to commisioning. This way det char people know when we left the IFO alone
For some alignment state your demod phase is bad such that you get multiple zero crossings in the error signal, and you jump between these two states.
Set intent bit to 'Commissioning' as per Sheila's request.
Some times ago I simulated the SRCL error signal as a function of the differential lensing in the two ITM substrate. The simulations was carried out for the full IFO, but maybe SRCL behavior is similar in DRMI. The bottom line is that some differential lensing (like the one we have because of the ITM substrate inhomogeneities) can cause multiple zeros in SRCL signal. This might explain the SCR hopping, if the SRCL residual motion is not small enough. See the attached animation, which I hope will work!
Congratulations all! This is a wonderful accomplishment.
just for bookkeeping purpose:
the DRMI locking trial was taken place from 5:00-ish to 6:14-ish UTC last night. The first lock was achieved at around 6:14:00 UTC followed by some frequent short locks for 10 minutes. After the first lock there were several good locks.
Sheila, Rana, Kiwamu, Alexa, Daniel
We had not been able to lock the PRMI all of today. During the day's usual ISI shaking we noticed that the AS beam had gone nearly of the camera and so spent awhile chasing trends, etc.
After not finding the cause of that, we noticed that the AS45 and REFL45 signals had dropped off to nothing around 3AM local time. As far as we can tell, no one was on site at the time.
Afer some hunting, we found a particularly horrible electronics setup for the 45 MHz modulation amplifier in the H1 CDS electronics room on the same rack as the 9 MHz Marconi generator:
There was an unsecured ZHL-1A amplifier on top of the rack, powered by a DC bench supply (of the lowest quality available), and connected by damaged Banana cables. The banana power cables are intermittent and turn off the amplifier power once in awhile. We could see the power supply current vary to any value between 0 and 400 mA as we brushed the cables - I wouldn't trust this amplifier any more.
Several people disavowed any knowledge of this setup (even after we found https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=11986). It contained a few low quality L-Com cables and several cheap BNC barrels. We must never use BNC connections and these kinds of unreliable adapters in our low noise RF setups. Only N and SMA connections are allowed.
We have relocked the PRMI after removing this setup. The modulation voltage for 45 MHz is now 4x lower. It would be best to make a higher quality RF amplifier setup underneath the PSL table as was done at LLO. We'll be using this weaker modulation for another few days, but we want the higher modulation depth by mid next week, when we get back to the 3f locking.
The attached screen shot shows the minute trends of the REFL and AS 45 over the last 48 hours. There is a dead time, which is when the modulation depth was zero, but suprisingly the peak to peak of the signals was not reduced by a factor of 12 dB as would be expected after the removal of the 6dB attenuator and the 19 dB amplifier.
Here's a 1-minute video of a PRMI sideband lock, from the AS port camera. Kiwamu, Rana, and Sheila will write more about this later in the evening.
Rana, Kiwamu,
In response to Sebastien's study of the BS motion, tonight we took a close look at the BS motion when the PRMI was locked and unlocked.
The conclusion is that:
it is the LSC feedback that has been shaking the angle of the BS below 100 mHz through some kind of L-to-A couplings.
(What to do)
We need to re-design better L-to-A decoupling filters to reduce the coupling. According to a transfer function measurement, the coupling coefficient was about 0.1 [rad at the bottom stage / meters at the M2 stage]. Because of this coupling, both pitch and yaw motion in the BS increased their RMS by a factor of three, mostly from components below 100 mHz. In order not to excite the angular motion more than they normally are, we roughly need another factor of three improvements in the existing L-to-A decoupling filters.
(Some plots)
The 1st plot show various spectra when the PRMI was locked on the sidebands. The upper plot of the 2nd attachment shows a comparison of the oplev signal with and without the PRMI locked. It is evident that the LSC feedback makes the spectra worse below 100 mHz. The rms increased up to 0.1 urad in rms. Also, the bottom plot of the same attachment shows the transfer function of the couplings from the M2 stage witness sensors to the bottom stage oplevs.
The commissioners have been complaining about too much motion in Yaw on the BS (almost 2microns peak to peak at 10 mHz (!!)).
We know we have some pick up between Z and RZ (see the various SEI logs from the last 6 months), so I switched from a ~100mHz blend in Z to a 750mHz. Relaxing the actuation in Z reduced the pick up seen in RZ.
I was afraid to degrade pitch with this change, but we improved yaw by a factor of ~5 without changing the pitch integrated RMS (it introduced a peak around 1Hz though).
I've tried to implement a 250mHz blend, but no improvement...
Thus, the configuration that seems to satisfy the commissioners is:
- Tbetter: X, Y, RX, RY
-Tcrappy: RZ
- T750: Z
I'll check what is the status of this "pick up" on the other chambers ASAP.
Yes, this was certainly better for PRMI stability.
We now need to work some more on the angular stability of the other loops. Peeking over Kiwamu's shoulder, I see that the RMS of the other DRMI mirrors is ~0.1 urad (for 0.01 < f < 0.5 Hz). We should tailor the ISI and HEPI loops to move this RMS down to lower frequencies (0.01-0.1 Hz) so that the WFS loops can handle it.
I think that this is the configuration that we want for now, one comment is that it would be worth plotting the oplev signals only up to 19Hz (or 10Hz or whatever frequency it is that cuts off that ugly peak), the 29Hz peak is room fans, I'm guessing that the 19Hz peak is an oplev pier resonance, then we could get an RMS that better represents the optic motion.
