Joseph B, Darkhan,

Overview

Updated settings of CAL-CS oscillators and filters that are used for calculating calibration line coherences. These coherences will be used to inform the validity of the DARM time-dependent parameters calculated in the front-end.

At the moment the coherence outputs are 0, once we accumulate data at "low-noise" we should see cal. line coherence and uncertainty values.

The changes have been "accepted" in safe.snap and observe.snap

Details

The most recent version of CAL-CS update (see LHO alog 27733, LLO alog 26491) enabled calibration line coherences and uncertainties calculations in the front-end. These calculations require demodulation of excitation and DARM_ERR channels at line frequencies, band-pass and low-pass filters (see DCC T1600349).

Following Python script is used to set synchronized oscillators (in the "line coherence" blocks of CAL-CS) and the filters:

/userapps/trunk/cal/common/scripts/set_coherence_h1.py

An oscillator (for coherence calculation) that replicates an ESD line oscillator in SUSETMY model was set manually (see Attachment 1). Ideally this oscillator should give an equivalent output to the ESD line oscillator (currently SUS-ETMY_LKIN_P_OSC), but their amplitude ratio is ~10% different at the moment (see Attachment 2). Needs investigation.

Note that a possible source of an issue is that ETMY_LKIN_P_OSC is not a synchronized one. This might mean that every time this oscillator restarts the phase of the demod. osc. in CAL-CS should be adjusted for a meaningful κ_T calculation.

A screenshot of ESD line coh. demodulator and filters setup (as an example) is given in Attachments 3. Attachments 4-7 show CAL_CS_TDEP_*_LINE# MEDM screens.

J. Kissel

As I'd seen charge continue to accumulate on the test masses (see LHO aLOG 28881), and we haven't been able to commission regular bias flipping since before ER9 (see LHO aLOGs 28362, 28152), I'd turned OFF the bias on the ETM ESDs last week Thursday (Aug 04) while we have HAM6 vented and the gate values are closed. 

After measuring charge today, this has had a noticeable effect on the accumulated charge, in that the majority of both test mass' quadrants show less accumulated charge. This may mean that leaving the bias OFF is just as effective at charge reduction as flipping the bias. 

I've left the BIAS OFF again after these measurements, to try to squeeze out as much more dissipation as I can.

However, I still highly recommend commissioning the ability to flip the bias sign, once we have the IFO back and stable.

Krishna

I've attached some plots showing the tilt measurements with Compact-BRS. The calibration is only approximate right now (+/-50%). More accurate calibration will happen soon.

Quick Tutorial:

Recall that the instrument consists of a beam-balance with two fiber interferometer readouts at left and right ends of the balance. The fiber-tips are located on a translation stage driven by a PZT stack each (100V, 11 micron range). Photodiodes (PDs) measure the output of the interferometers. The PZTs are used in a low-frequency feedback loop to keep the PDs at mid-fringe. The low-frequency tilt signal is therefore in the PZTs, while the high frequency seismic tilt is in the PDs. The raw displacement signal is converted to angle by dividing by the arm-length (roughly 15 cm from the center). The beam-balance is also damped with capacitive actuators using the PZT control signals.

The fiber interferometers are operated with a large gap (using a collimating lens) and thus are individually limited by the frequency noise of the common laser. However, taking the difference of the PD signals allows us to subtract frequency noise to the extent that the cavity lengths are matched. Crudely,

PD 1 = Angle + L1 * Frequency noise

PD 2 = -Angle + L2 * Frequency noise

Therefore,

SUM = (PD1+PD2)/2 = Frequency noise*(L1+L2)/2

and DIFF = (PD1-PD2)/2 = Angle + Frequency noise*(L1-L2)/2

The attached plots show data measured this afternoon. The first plot shows the PZT and PD signals for each cavity. After the flexure replacement on Monday, the instrument is slowly settling but is continuing to drift in one direction as seen from the plot.

The second plot shows the ASD of these four signals. As explained above, the tilt at higher frequencies is in the PDs and the low-frequency tilt is in the PZTs.

The third plot shows the ASD of the SUM and DIFF channels. Note the smooth 1/rt(f)-ish slope in the SUM channel (at low frequencies) indicating that it is limited by the frequency noise, as expected. Unfortunately, there appears to be excess noise above 10 Hz, which look like acoustic pickup of some sort. This was taken during a noisy LVEA, so it is possible that after the clean room fans are turned off and it gets quieter, the noise will go down. The DIFF, does dip below the SUM as expected - indicating that we are getting some frequency noise suppression. It is not clear what the noise floor of the DIFF channel is yet. IF there is a factor of ~3 frequency noise suppression (at a minimum), then the noise floor ought to be a factor of 3 below the SUM channel (~ 30 picorad/rt(Hz) at 10 Hz). But if we are limited by acoustic noise, then the noise floor could be worse.

The fourth plot shows coherences between some interesting channels.

Compact BRS is performing reasonably well at the moment. Stay tuned for more data/plots when things are quieter. I'll also try to compare c-BRS with other local sensors.

Krishna

I measured the tilt transfer function (normalized to 1 at high frequencies) for Compact-BRS yesterday by driving it with a piezo stack located under it's platform. The drive would produce both rotation and vertical motion of the platform, but as d is expected to be small, only the rotational drive is relevant. The first pdf shows the response of the instrument compared to the drive at five frequencies - four to the left of the resonance and one to the right (used to normalize the TF). The resonance was at ~62 mHz and the measurement suggested a d = 100 (+/-10) microns. The error bars and limits are rough estimates and not exact. This sugggested an addition of ~3.8 grams to the upper mass to reduce d and obtain a final frequency of 47 mHz.

After a few attempts at trying to adjust the frequency (mainly due to inaccurate frequency measurements), I finally got it close to 49 mHz, which I deemed to be sufficient. The new transfer function measurement yielded the second plot, indicating d = 11 +/-2 microns. For this value of d, the translation rejection is given by M*d/I = 4.9 kg*11e-6m / (0.08 kg m^2) = 7e-4 rad/m. 

This is much better than needed for high frequency (>1 Hz) seismic tilt measurement, where seismic wa5velengths are short and consequently the tilt (in rad) is substantial in comparison to the translaiton (in m) . At 10 Hz, for example, the wavelength is 20 m, therefore a translation amplitude of 1 nm has an associated tilt of ~ 0.3 nrad. A more patient and careful tuning process can reduce d below +-1 micron.

Opened exhaust check-valve bypass-valve, opened LLCV bypass-valve 1/2 turn -> LN2 @ exhaust in 16 minutes 20 seconds -> Restored configuration to as found.  

Next CP3 overfill to be Friday, Aug 12th.

On 8/8 I checked the PSL chillers, per work order 6482, and found that the crystal chiller was a bit low,  so I added 100ml of water.  The diode chilller was not in alarm, so I did not add water to it.

Summary:

• crystal chilller +100ml
• diode chilller nothing added

Hugh, Jim

This morning Hugh and I went out and rebalanced the ISI. We removed some weight from the sides to compensate for buoyancy, something we missed last time. Now the ISI should have less DC drive in vacuum, before it was holding a 40 micron offset in Z, should be more like 10-15 now.

TFs were taken this morning, and other than missing the dewhitening setting on the GS-13s (HAM6 runs in low-low gain with dewhitening off to avoid tripping when the toaster pops) the TFs look the same as a measurement I took in 2014. Attached plots are GS13s, blue, brown, light blue are the current measurements, red, green and pink are the 2014 refs.

WP #6069

To allow copying of raw minute trend files from the h1tw1 SSD RAID, the existing raw minute trend directory was renamed and a new directory created.  This required restarting the h1nds1 daqd process to add the new directory path.  This will need to be done again when the copying is completed.

Work Permits Summary, Maintenance Day 2016 August 9

   Found the FSS AUTOLOCK was oscillating. Could not adjust the gain due to Guardian control. 

Per Jason:
   (1). Took the Guardian node PSL_FSS to AUTO
   (2). Set the state to IDLE
   (3). Adjust the COMMON GAIN to 16dB
   (4). Set the state to READY_FOR_MC_LOCK

 Jason and TJ are looking into an elegant long term solution.   


  
  

Topped off the Crystal Chiller to 155mL (it seems whenever I took it to the MAX level, it would immediately drop. So I took it to max twice and called it good....and then it dropped.)  

Diode Chiller had no alarm.

[Corey, Betsy, Fil, Peter, Calum, Stefan, Koji]

Summary

- The ISC portion of the HAM6 vent work has been completed.

- Shield isolation of the in-vacuum cables was confirmed.

- The fast shutter was reinstalled on the table after some modifications.

=> Ready for the SEI mass balancing and other exiting procedures. OMC PZT HV is still on. Remeber to turn it off before pumping down.

Some details

- Shield isolation: It is always confusing to check the shiels isolation on HAM6 because of several reasons.

1. All the OMC cables (OMC DCPDs, OMC QPDs, and OMC PZT) are sharing their shield on the OMC breadboard. Therefore one needs to remove the related three DB25 cables from the flange when the shield shorting is checked for them.
2. The beam diverters connects the shields of their cables shorted to the ISI table. Therefore the shorting needs to be checked with the beam diverter disconnected at the mighty mouse connectors. When the test is done, the connectors need to be restored and the function of the beam diverters should be checked again.
3. The picomotors don't short the shields on the table. Check them as usual.

We initially had several cables shorting to the chamber but all of them but one happened at the slack of the cables right inside of the flange. The last one happened on the DB25 cable before it climb up to the vertical wall of the ISI.

- The fast shutter modification / reinstallation

(Photos are supposed to come later.)

1. The new bobbin came in for replacing the moving part of the shutter.
2. The wire stays were modified to have the bobbin wires more relaxed. Also it should allow us to have more clearance of the wires from the beam towards OM1.
3. To allow this modification, the direction of a coil wire (shorter, negative, lower slot) in the terminal block was flipped (Corey's attachment 1).
4. The shutter was placed on the ISI table. Then we found that clearance of the wire is in fact poor. We bent one of the wire clamps (Corey's attachment 2: The clamp at the right side of the shutter) and also adjusted the wire length to have 8~9mm clearance from the beam now. (Corey's attachment 3: The clearance does not look great in the photo but in reality the beam is clearly away from the wire.)
5. The shutter function was tested with the shutter test controller. No HV was used during the test.
6. The beam alignment from the shutter to the gold coated tube was checked. The beam is on the tube but close to the top edge of the tube aperture when the shutter mirror wobbles. We believe this does not create any issue even if the beam falls off from the dump as there is nothing sensitive behind the tube beam dump.
7. Related to the entry  LHO ALOG 28958, we found the shutter height was too low. The distance between the top of the shutter mirror and the beam was ~9mm. The nominal distance is 6mm. We adjusted the height of the shutter to have the nominal height. (Corey's attachment 4)

Bubba, Jim, Dave:

UNIT-1 cooling in the MSR developed a very noisy fan this afternoon. It has been opened as FRS-6039. This system was turned off and the other two units had their set points reduced from 70F to 67F after the room became noticably warmer.

The room temperature can be monitored via the Beckhoff channels H1:pEM-C_MSR_RACK[1,2]_TEMPERATURE. It shows the temp increased from 18C to 26C (64F to 78F).

I was taking some measurements on the BSCs earlier today, and I noticed a feature at about .73 hz in the OAF CARM and DARM suspoint channels that didn't show up in the OAF MICH suspoint spectra. I then looked at the GS13s on ETMY and there is a pretty sharp feature that seemed to have appeared after recovery this morning. A quick cruise through the Summary pages, though, showed that there is some intermittent feature that  has been there off and on since at least the end of June. I thought it might be the RX/RY loops on ST2 I've been trying, but turning those off had no effect. I then took the ISI St2 to damped, but the feature was still there. Jeff said that the TMS has a resonance about .73 hz, so I turned the damping off and that made the feature much worse, but it also rang up a bunch of other features. Whatever this is, it has to be very intermittent since I hadn't noticed it before today, and I look at ETMY pretty frequently, and I've never noticed it before.

Attached plot is the ST2 RX GS13, which showed this the strongest, though RY and Y also saw it. The CPS also saw this in all configurations, even damped. The TMS sees this, though not as big, and the quad sees even less and only in pitch. ST1 of the ISI does not see this.