Krishna,

The location of the c-BRS is shown in the attached map, indicated by the green '+'. The center of the instrument is very closely aligned with the center of the ITMX BSC chamber along the x direction and is located ~ 46 cm (18 inches) from the horizontal beam between the piers (seen a little below the green + sign).

c-BRS Locking Instructions

The attached screenshot shows the MEDM screen to control c-BRS. The control flow is described in T1600325. The two interferometer cavities are locked using the PZT1 and PZT2 filter boxes. The second cavity feedback signal is used to apply damping to the beam-balance. If the outputs of the PZT control signals (top right) look railed, this indicates that the beam-balance has drifted out of the range of the piezos. We can reset the range simply by locking to a different fringe as described below.

1. First, turn off damping, by setting the gain of the DAMP filter box to 0.

2. Open PZT1. Set Gain to 0. The ramp time should be set to 3 s.

3. Hit 'CLEAR HISTORY'. Now turn the PZT1 Gain back to 0.25. First cavity should be locked.

4. Open PZT2. Set Gain to 0. The ramp time should be set to 3 s.

5. Hit 'CLEAR HISTORY'. Now turn the PZT2 Gain back to 0.25. Second cavity should be locked.

6. Wait at least 30s and then set the DAMP Gain to 0.1 This sets the Q of the beam-balance to ~20, as opposed to the natural Q of ~150.

Note that if we know the direction of the drift, the Piezo offset can be set to take advantage of that fact. Currently the Piezo 1 drifts negative hence the Piezo 1 offset is set close to the positive maximum (2^17 ~ 130,000 cts) and vice versa for Piezo 2. I expect that this drift will go away in a few days time and then we will just have the normal daily temperature modulation, in which case the PZT offsets could be set to 0.

Krishna

Here are the recorded c-BRS associated channels and their calibrations (I think it is accurate to <20%):

1. H1:NGN-CS_CBRS_RY_PZT1_CTRL_IN1_DQ  :   PhotoDiode 1 output  :  1.6e-10 rad/count

2. H1:NGN-CS_CBRS_RY_PZT1_MASTER_OUT_DQ : PZT1 output  :  2.8e-10 rad/count

3. H1:NGN-CS_CBRS_RY_PZT2_CTRL_IN1_DQ  :   PhotoDiode 2 output  :  1.23e-10 rad/count

4. H1:NGN-CS_CBRS_RY_PZT2_MASTER_OUT_DQ : PZT2 output  :  2.8e-10 rad/count

I've also attached more spectra recorded this morning after the clean room fans were turned off. Many of the noise peaks went away, especially above 100 Hz, but some lines remain which are common to the seismometers and c-BRS. The DIFF signal above 100 Hz, drops to ~10 picorad/rt(Hz), indicating that it's noise floor is indeed well below the SUM channel. I expect that the current SNR at ~10 Hz is between 10-30. I've attached Matlab code showing the analysis.

Recent mods to the ETM ESDs (alog 28939) allow PI signals to drive even while ETM ESD is in the HV mode. I've edited the SUS_PI and ISC_LOCK guardians to account for this. Both reloaded successfully.

Previously the PI damping path for ETMs required the ESD be in LV mode == not be in HV mode. Because of this, we could not damp PI on ETMX until the ISC_LOCK state LOWNOISE_ESD_ETMY (as prior to this we are actively using ETMX ESD in HV mode for lock aquisition). PI damping for the 3 other test masses was turned on during DC_READOUT. ECR E1600230 now allows PI drive even when the LV driver is in HV mode. Now all damping turns on during DC_READOUT. 

J. Kissel

I had told the HAM6 team verbally (and even signed a piece of paper indicating) that all HAM6 SUS were freely suspended before the doors went on, but forgot to put in an aLOG about it. Mia culpa! 
 
Anyways, for the record: the in-air, after re-installation of the OMC shroud was complete, just before chamber close, transfer functions of H1 SUS OMC, OM1, OM2, and OM3 (still) look great. See attached .pdfs.

We need one more check after HAM6 is pumped down, and then we can declare victory.

Per E1600247 and ECR1600246, the following electronics were modified or relocated:

HAM6 shutter controller S1203609 was relocated from ISCT6 table (top) to rack ISC-R5, slot U2/3.

Changed R23 from 26.7K ohms to 12.4Kohms in the QPD transimpedance amplifier chassis S1301506. This was to increase the maximum threshold for the AS port trigger PD as seen by the shutter controller. See alog entry.

Cabling to ISCT table has been reconnected. The high voltage supplies for both the fast shutter and PZT are now power on.

PT-523 cold cathode vacuum gauge tripped around 10am. I restarted it from the controls console and then noticed PT-510 tripped. I restarted that one too. Looks like the pirani gauges spiked which caused the CC trip.

J. Oberling, J. Bartlett, P. King (from Pasadena)

Jeff came in this morning and found the PSL to be off.  Trends indicated the laser turned off at around 3:25 am PDT, with errors showing the flow was zero and the NPRO was turned off (no power watchdogs were tripped); the crystal chiller was found to be off, while the diode chiller was still running.  The crystal chiller was restarted and allowed to run for ~15 minutes and no glitches or errors were seen (last time we had a flow problem the chiller would glitch when just running by itself, no laser).

In discussion with Peter he suggested the possibility of the NPRO tripping (likely due to a power glitch or a glitch from the UPS).  When this happens the NPRO power supply, located in the PSL rack in the LVEA, needs to be manually re-enabled.  Upon inspection, the NPRO power supply indeed had to be manually re-enabled, which points to either a power glitch or a glitch of the UPS the NPRO is plugged into.  We don't think it's a power glitch as that would cause issues with other IFO systems, and this was not seen.  This leaves the most likely culprit at this time as a glitch from the NPRO UPS.

The laser is now back up and running, all stabilization systems enabled.  I took this opportunity to reset the HPO LRA back to its reference position and reset the relock counter for the injection locking system.

Arm GV 5 & 7 are now open. Closed WPs 6030 and 6075.

Cracked the gate annulus valve to let AIP pump any outgassing build up in that space. GV7's AIP showed no change. GV5's AIP rose to 5 mA and then settled back down to 1 mA after a few seconds.

Shut down purge air station and booster pump. Left compressor energized. Closed WP 6026.

I raised CP3's LLCV from 17% to 18% since it took 16 min. to overfill yesterday.

HAM 6 N & S doors and gauge assembly are leak tight. Attached is pump down curve.

We will open GV 5 & 7 after the ISCT6 table is positioned and all viewport work is complete. 

Notice from LIGO Systems

Due to the failure of the fast shutter system on WHAM6 and the damage done to the OMC, we will be operating under the following conditions:

The input power is to be kept to less than 25 W.

Tests of the fast shutter system shall be made on a regular schedule to verify its readiness.

This exceptional condition of operation will remain in place until a TRB (technical review board, reporting to Systems) has reviewed the risks to the OMC, the failure mechanisms, and the methods to deal with them (both administrative and engineering based). The TRB will then issue a return to normal operations order.  We expect and hope that these issues can be resolved quickly and commissioning will resume at the 50 W power level.

Adjacent pump port volumes isolated after Turbo at full speed, Aux. pump carts at HAM5 and HAM6 annulus pump ports pumping combined annulus volume in parallel.  Corner Station vent/purge air supply left running in the event that final leak testing tomorrow results in a needed vent cycle to fix leak.  

Also, Y-end RGA bake cycle completed (maybe get background scans tomorrow - crisis permitting!) 

1840 hrs. local -> Leaving site now.

Gerardo, Kyle, Chandra (and Bubba on doors)

Started pumping down HAM 6 with rough pump at 5:10pm local. Kyle graciously offered to stay late until system can transition to turbo pump. Thursday morning Chandra will leak check the new gauge assembly. Crew can connect ISCT6 table first thing in the morning. If all is well with leak check, gate valves can be opened in the morning following leak check.

Expect pump noise for over a week from maglev turbo on top of HAM 6 and 2-3 aux carts - pumping on annuli and one at vertex RGA (between HAM 4 & 5).

Thank you Bubba for helping install doors today! We spotted a new nick on north door at 4 o'clock position in the path of the outer o-ring but leak checking confirmed there is no leak. We leak checked both north and south doors by pumping on the annulus volume.

Dew point of chamber during blow down was -19.9 deg C.

Gerardo & Kyle took some particle count measurements at south side after north door was sealed. They can report the #s.

New wide range ion gauge was installed. Thanks Richard and Fil and others for running cables/power and rebooting for immediate monitoring!

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.