The power supplies in the I/O chassis are magnetically noisy and can couple to internal boards and the signal and power cables and connectors that are near the I/O chassis (here). CDS set up a test stand with a BNC AA chassis connected to an I/O box for testing a new type of power supply.  Figure 1 is a photograph of the setup with the old supply (box in the back corner) and new supply (card with the gloved magnetometer on it). I was able to switch back and forth between the supplies. Two of the channels passing through the I/O box were used, one to carry the magnetometer signal, and a blank channel that was terminated at the AA chassis input. Figure 2 shows the spectra of the magnetometer channel for each power supply (the magnetometer was moved back and forth to sit on the active supply), and the coherence between the magnetometer channel and the blank channel.  The magnetic field from the old supply can be orders of magnitude larger than that of the new supply over broad regions. The old supply also displays the drifting features of beating high frequency oscillators.  The new supply only showed coherence at harmonics of 60 Hz while the old one impressed several lines and a region of increased coherence onto the blank channel. When the new supply was used, the blank channel level was a little lower, and did not have the drifting features most likely produced by beating high frequency oscillators in the old power supply (Figure 3). 

The second problem with the I/O chassis is that the fans at the front produce peaks in the channels that pass through it by power supply ripple (here - the peaks go away when a separate supply is used for the fans). Figure 3 shows that these fan peaks are present with both the old and the new power supply. One possible configuration to test is to power the fans directly off of the power supply card instead of off of the main board.

Robert, Richard, Dave, Jim

One of the accelerometers on the PSL table (PEM-CS_ACC_PSL_TABLE2_Z) is glitching once per second. The other accelerometers don't seem to have this problem. We noticed this because it was messing up our hVeto results. I searched for where these started, and as far as I can tell it's Apr 14 2:30 UTC (that's 7 PM on Monday local, I think). The onset takes a few minutes.

The first plot is an Omega scan from a few hours ago, showing the glitching. The second is a spectrogram of the onset.

We are seeing something similar in some of the ISI GS13s (maybe only ones in the center building?). They also have a once per second glitch, though it's not clear if it's related. Detchar will track that down more, and I'll alog it separately.

We've known for a while now that we can move the ITMs (ITMX pitch goes down by several urad, iTMY up by about 1 urad) to get a recycling gain of 32-33, but we've seen that the IFO isn't stable like this.  Elli looked into two sudden lockloss that happened after we tuned up the recycling gain on Thursday, (17921 ) and saw that something is going wrong in the MICH loops (both LSC and ASC) before the lockloss.  Yesterday, Gabriele Evan and I noticed that the MICH LSC loop was marginal in the final low noise state, Gabriele designed a filter (called comp, in FM10 of the MICH bank.) to make the loop more stable. (before and after screen shot atached)

Today I tried a few more times to increase the recycling gain, we were locked for about 20 minutes with a recycling gain of 32.5, but most of the day we have had unexplained locklosses and difficulty locking, both with and without improved recycling gain.  I've edited the guardian to request 10 Watts instead of 15 and leave things trying to lock.  

Posting here to inform everyone of one or more possible failed disks in the LLO aLOG disk array.  I am headed to the site now to investigate.

Today at 10:40 am the turbo was spun down and the scroll pump turned off, turbo pump cable still connected, will remove it on Tuesday.

The ion pump for HAM6 was able to mantain the pressure on its own, the pressure keeps going down, see attachment.

Data for the past 3 days.

Arnaud posted about CPS glitches in the CPS HAM5.  Though it prudent to scan LHO for similar.

I looked over the past three weeks and found none that were shaped like LLO (very narrow spikes to near 40k counts.)  WHAM6 had some associated with the fast shutter although I did not establish cause/effect there.

WHAMs 2 3 4 & 5 all had one exceeding 20k counts at the same time 0030 utc 30 March but was not a single spike, looks more like an Earthquake.  Bottom line, we should be ever vigilent but for now, LHOs HAM CPSs are not glitching.

LVEA: Laser Hazard
Observation Bit: Commissioning   

07:00 Karen & Cris – Cleaning in the LVEA
10:05 John & 3IFO Group – in LVEA taking measurements at beam tube building exits
10:18 Gerardo – At HAM6 to turn off scroll pump
10:30 ISS FSS have been saturation and the IMC is dropping out of lock. Per Peter K. turned off the ISS Autolock to see if that stabilizes the FSS and IMC.  
10:43 John & Co – Out of LVEA
10:45 Gerardo – Out of LVEA
12:20 FSS is still saturating and the IMC is dropping out of lock. Per Peter K. dropped the FSS Common Gain from 25 dB to 24 dB. 
15:08 Gerardo – Going to H2-PSL enclosure

Below are trends from the past 10 days

As reported in last night entry, we tried to improve the SRCL noise coupling non stationarity by increasing the low frequency gain of the DHARD Yaw loop. In my initial elog entry, I pointed out that the SRCL coupling was fluctuating following ASC-AS_A_RF45_I_YAW_OUT. However, it turned out that this signal is basically equal to the DHARD yaw error signal. Most of the SRCL coupling fluctuations and residual motion of DHARD are at frequencies below 200 mHz, so I designed a boost to increase the low frequency gain of the loop. The improvement is visible in the first attachment (green without boost, red with boost). The loop accuracy improved significantly, as shown in the second sttachment, which is a time series of the error signal.

With this new loop, Evan injected some SRCL noise and I could do the same analysis I did yesterday to study the SRCL coupling non stationarity. Here are my main comments:

• contrarily to what stated in last night entry, the SRCL coupling is both lower and more stationary. The third attachment shows the SRCL coupling gain (average of the TF in the 100 Hz region) as a function of time. It is on average about 3.5e-11 and fluctuating by some 2e-11. Before DHARD boosting, the coupling was fluctuating between -10e-11 and +27e-11.
• Now the channel ranking gives a different answer: SRCL coupling is mostly modulated like ASC-AS_A_RF36_Q_PIT, and only partially as DHARD YAW. So it seems that we removed most of the fluctuations caused by DHARD, but now we have some other loops to improve. If I'm not mistaken, AS36 signals should be used to control some SRC degree of freedoms

This morning after some full lock attempts, the IMC was found to be so misaligned that it did not lock any more. It turned out that this was due to the integrators in IMCASC which kept integrating the intentional offsets that Gabriele had implemented (alog 17888). In order to resolve this issue, we edited the IMC_LOCK guardian so that it disables and enables the offsets when state is DOWN and LOCKED respectively.

Summary: Been going on since late February (~2-24) at ~24 hour period (last week at least.)  It is not obvious in the In-Loop or Out-of-Loop HEPI position sensors second trends.

See attached for 70 day trends showing the glitch being revealed after getting the sensor quiet (got lucky) and continuing to today.  Second plot zooms into glitch early this week 4-12 ~0400utc.  This one is a double glitch; they are not always the same but the first three this week are the sign and about the same magnitude.

Still looking for cause and other potential affects.

It is not incessent but the EndX HEPI Pressure still alarms occasionally at +-3.5 degrees F.  So I've opened the no-alarm region to +-4 degrees F.  See the attached plot for 1 weeks worth of minute trends.  You can see that this change should reduce the number of alarms from several a week to one or less.

Notice how much noisier the EX pressure is than EY or the Corner and the imprinted increase in the controller output.  It would be good to quiet down this signal.  EE is working on getting another (possibly custom) power supply.  Also, what is up with that ~24 hour glitch that hits the EY--warrants investigation.

Nice to see the daily changes on the controller output, presumably based on the temperature.  The last column of pressures are out of loop in the mechanical room, I thought those might have shown the cyclic signal too but they don't.  Does that mean the temperature isn't that important or is the temp in the MR as well controlled as the VEA...?

Sheila, Koji, Robert, Evan, Alexa, Dan

We have made several measurements of backscattering from the OMC.  It seems like the reflectivity of the OMC is smaller by a factor of about 20 than what was seen at LLO, and it seems that backscatter from the OMC is probably not limiting our DARM spectrum.  

Two nights ago, we measured fringe wrapping by exciting the OMC suspension in the longitudnal direction, as well as by exciting OM1.  (related alogs 17910 17904 17882)  The attached plots show the DCPD RIM, with the DARM loop supression removed, with the excitations on.  

• First, we noticed that the osem calibration must be wrong, for both OM1 and the OMC.  For the OMC our knee frequency around 45 Hz indicates that indicates that our excitation amplitude was about 35.25 um.  The osem readback  indicates that our exitation amplitude was 11.8um, if we assume that this path length is double passed the osem is underestimating the motion by about 50%.  The story for OM1 is similar, the osem indicates that OM1 was moving with an amplitude of 6.25 um, but the path length modulation must have been about 20 um based on the knee frequency.  (Tobin's thesis, p 45)
• When we excite the OMC, we see two scattring shelves, the second has a finge velocity twice that of the first path.  For the first shelf we get an amplitude reflectivity of 1e-5, for the second shelf it is 1e-6.  These are eyeball fits, but they seem to be good to within about 15%.  At LLO (alog 13607) similar measurements showed an r = 2e-4 for their first shelf.  
• One speculation is that the first shelf could come from scattering within the OMC itself, and the second from the OMC refl path. Yesterday (after these measurements were made) Koji realinged the OMC refl QODs, and the amplitude of the second shelf is reduced today.
• FOR OM1 we only see one shelf, because OM1 is not the scattering source.  With this we are only modulating the path length between the IFO and the scattering source.  However, we measure the same reflectivity as the first shelf when exciting the OMC, so the two measurements are consisitent.

Tonight Jeff made a test of turning off the HAM6 sensor correction, as was done at LLO (third attachment) (LLO alogs 16814).  The spectrum is attached, but we do not see the dramatic fringe wrapping seen at LLO.  We would expect the impact to be smaller here than in LLO because our scattering amplitude is smaller and it is also likely that the microseism could have been smaller here.  

Today we Robert Koji and I made injections into all 6 DOFs on the OMC to see fringe wrapping.  We saw nothing by exciting roll or vertical, we were able to produce shelves by exciting L, T, P and Y.  The last screenshot attached shows the sectra with the various excitations on. For the record, here are times, all excitations were at 0.2 Hz, into the test filter banks.  While I've attached spectra of these, several off these shelves were moving around durring the measurement because of some lower frequency motion. 

Koji, Evan

Summary

MICH feedforward seems to be doing its job, although there is room for improvement by implementing a frequency-dependent subtraction.

SRCL coupling into DARM seems to be very nonstationary. Consequently, the feedforward is not working.

Details

We injected band-limited white noise (elliptic bandpass, 10 Hz to 1 kHz, 6 ct amplitude) first into MICH, then into SRCL, to test the feedforward that was implemented a few weeks ago.

For MICH, frequency-independent subtraction is fair to middling (red) compared to no subtraction (blue); at best we get 20 dB of subtraction around 150 Hz. Note that the TFs in this plot use the whitened DARM channel. The whitening is undone for the spectra in the fourth pad.

For SRCL, the 1/f² feedforward via ITMY L2 gives no subtraction at all. The attachment shows the TF of SRCL control → DARM with the feedforward off and with broadband noise injected into the SRCL error point. Unlike MICH, appearance of this excitation in DARM is highly nonstationary, fluctuating by a factor of 2 or so in a frequency-dependent way. Additionally, the coherence is poor above 20 Hz, despite the excitation elevating the DARM noise by more than an order of magnitude from 20 to 100 Hz.

The shape of the excess noise is more or less the shape of the 100 Hz elliptic cutoff that we put into SRCL a few weeks ago. Is it possible that the SRCL control noise explains the nonstationary, 100 Hz "scattering" shelf that we've seen in the DARM spectrum this past week?

This seismometer has given us problems for some time: alogs 15510, 14482, 9727.  JeffK may point to others too.

On the attached four plots, there are four successive days, Saturday thru Tuesday at 0100pdt.  The lower left panels are the Coherences between the HAM2 & HAM5 (STS-A & C) and the ITMY (STS2.)  The Upper Left, Upper Right, and Lower Right panels are the ASDs of the X Y & Z DOFs respectively of STS2 A B & C.

The take away is that in general the character of the ITMY (STS2-B) ground seismometer doesn't change like the other two instruments below 100mhz while the HAM2 & HAM5 instruments change more day to day and mostly look like each other.

Details:  The Z DOF is most obvious in that below 50 or 80 mhz, ITMY trends up steeply while the A & C seismos do not.  For the Y DOF, the HAM2 (STS2-B) signal seems to be the outlier but the day to day doesn't follow a patten between the instruments so I ...  The X DOF is pretty good with the A & C instruments tracking each other pretty closely while the B sensor kinda stays at the same power level, mostly.  So, like I say, a Case, maybe.

Two tip-tilts have been assembled for 40m.  They are sitting on the optics bench in the Optics lab.

These have thinner wire (43 microns in diameter) to avoid the hysterises seen in the thicker 125 micron wire.  Therefore these have to be handled more carefully.  The wires are quite unforgiving of any kinks or handling errors.

As agreed, these do not contain BOSEMs.  Type-B (one stage before the production line)  bosems will eventually be used in these.

The tip-tilts are ready for shipment to 40m.  They have been wrapped in Al-foil.  For long term storage, these have to be stored in a dry atmosphere to avoid rusting of the "piano wire" fibers.  The mirror holders are locked into place for shipment using the eddy current dampers on either side of the mirror mounts. 

The Sl nos are 007 and 038 (Bottom Plate).  Images of the assembled tip-tilts and their various reference numbers are attached.