[Koji, gautam]

Summary:

We are ready to put the heavy doors back on the chambers and do some test pumpdowns tomorrow morning if Jon gives us the go-ahead. Also, Koji made the OMC resonate some of the AUX beam light we send into it

Details:

1. EY work:
   • IMC was locked, and we attempted to locate the beam with an IR card inside the chamber.
   • Koji found that the beam was too high, we were over-shooting the entire black-glass baffle on the EY table.
   • So I moved the TTs to try and center the beam through the aperture of aforementioned baffle.
   • Once this was done, we found that the beam was misaligned in yaw by ~1-inch in transmission on the EY optics table (there was an iris in place marking the cavity transmission axis). This explains why I couldn't find any TRY flashes while moving the TTs around.
   • We hypothesize that without the 2 degree ETM wedge in place, there isn't a compatible axis for the ITM transmission to also make it through the EY baffle and transmission iris. Over ~1m, the 2 degree wedge makes roughly 1.4 inch translation in yaw, so this seems to be a plausible hypothesis.
   • The ETMY suspension was moved from the mini-cleanroom setup back into the EY vacuum chamber. Two clamps (finger tightened only) hold it in place on the NE edge of the optical table. We decided that this is a better resting palce for the cage over the holidays than an in-air cleanroom.
2. OMC chamber work:
   • While we were in clean garb, we decided to also investigate the OMC situation a bit.
   • It quickly became apparent that it was hopeless for me to work in chamber in the tightly confined IOO chamber. So Koji went in to have a look.
   • Koji will post the detailed alignment procedure - but after some alignment of the AUX laser input beam axis using in air steering mirrors and Koji's expert tweaking of the pointing into the OMC, we observed some resonances of the OMC.
   • Attachment #1 shows the full-range triangle ramp applied to the OMC length PZT (top row) and the OMC REFL signal (bottom row), measured using a PDA520 (chosen for its large active area) connected to a scope (AC-coupled, 1Mohm impedance, averaged to make the dips more prominent).
   • The OMC transmission was also (barely) visible on an IR card.
   • So the OMC length PZT seems capable of sweeping the length of the cavity. Based on the size of the dips we saw, the MM into the cavity is sub 1-percent.
   • The transmission PDs didn't output any measurable signal - but I'm not sure that the satellite box / readout electronics have been carefully characterized on the electroncis bench, so that will have to be done first.
   • We replaced the copper cover of the OMC (finger tightened for now) in case we do any test pumpdowns tomorrow. HV supply has been turned off, and the AUX laser has been reverted to standby mode.

I did the following:

1. Checked the ETMY OSEM sensing matrix and OSEM actuation matrix - more on this later, but everything seems much more reasonable than it was prior to this vent.
2. Checked that the IMC could be locked with the low-power beam
3. Aligned the Y-arm cavity using the green beam. Then tweaked the TT1/TT2 alignment until I saw IR flashes in TRY.
4. Repeated #2 for the X arm, using the BS to control the beam pointing.
5. Confirmed that the AS beam makes it out of the vacuum. It is only ~30uW in a large (~1cm dia) beam, so not the clearest spot on an IR card, but looks pretty clean, no evidence of clipping. I removed an ND filter on the AS port camera in order to better see the beam on the CRT monitor, this should be re-installed prior to ramping the input power to the IMC again.
6. With the PRM aligned, I confirmed that I could see resonant flashes in the POP QPD.
7. With the SRM aligned, I confirmed that I could see SRC cavity flashes on the AS camera.

I think this completes the pre-pumpdown alignment checks we usually do. The detailed plan for tomorrow is here: please have a look and lmk if I missed something. 

 IFO  P1=1mT PSL shutter is opened

 The pumpdown has started at 8:38am

Manasa was here to confirm good alignment of the IFO

Inner jam nuts of AC bellow were torqued to 45 ft/lbs and   door nuts were check on opened chambers.

Annulos were roughed down to 500 mTorr

Oplev servos turned off, PSL and green shutters closed before pumpdown started

[JC, Radhika]

The vacuum system went down over the weekend due to a loss of N2 pressure (We are down to our last tank of N2). I have brought the vacuum system back up to nominal state.

I first changed the N2 cylinder and to suopply the valves. WITHOUT N2, THE VALVES WILL NOT OPEN.  Normal operation PSI for N2 is ~65-80 PSI, view this from C1:VAC-N2_pressure. After swapping out the tanks I proceeded to pump down the vacuum with a simple procedure,

- First, opened V4 and V5
- Open VASE, VASV, VABSSCI, VABSSCO, VAEV, VAEE
- Open VA6
- Open V1 to pump down the main volume.

All the turbopumps are running at nominal speed and we are pumping down nicely.

 Cold cathode gauge CC1 -h (horizontal) just coming on 9.2e-5 Torr

P2 is the fore line pressure of the maglev. One can see the 4 Torr load during switching over to turbo pumping.

CC4  5e-9 Torr is the performance of the maglev pumping on the RGA only.

The annuloses are not pumped  now.  They are closed off to see how much outgassing plus leak they have.

Configuration: vacuum normal, annuloses not  pumped

Condition: normal

Precondition: 14 days at atm, IOO chamber north door was taken off as a new entrance, the ETMX chamber was not opened.

What is new in the vacuum system: new P1 pirani gauge, gold plated clean allen wrench and ..........what else was dropped?

Note: the wireless laptop did not fail once all day yesterday. I want to give credit to the person who is responsible for this.

[chub, bob, gautam]

1. Steps described in previous elog were carried out
2. EY heavy door was put on at about 1130am.
3. Pumpdown commenced at ~noon. We are going down at ~3 torr/min.

[jon, koji, gautam]

1. IFO is at ~1 mtorr, but pressure is slowly rising because of outgassing presumably (we valved off the turbos from the main volume)
2. Everything went smooth -
   • 760 torr to 500 mtorr took ~7 hours (we deliberately kept a slow pump rate)
   • TP3 current was found to rise above 1 A easily as we opened RV2 during the turbo pumping phase, particularly in going from 500 mtorr to 10 mtorr, so we just ran TP2 more aggressively rather than change the interlock condition.
   • The pumpspool is isolated from the main volume - TP1-3 are running (TP2 and TP3 are on Standby mode) but are only exposed to the small pumpspool volume and RGA volume).
   • RP1 and RP3 were turned off, and the manual roughing line was disconnected.
   • We will resume the pumping on Monday.

I'm leaving all suspension watchdogs tripped over the weekend as part of the suspension diagonalization campaign...

Pumping again after 7 days at atmosphere.

BS, ITMY and OMC chambers were open only.

Checked: jam nuts, viewport covers and beam shutters.

Oplev servo turned off and medm screens shots taken.

New item in vacuum:  green shade 14 glass beam block at IR-input [ from the PSL ] viewport to block green reflection-scatter.

Reminder: viewport is not AR coated for green!

IFO pressure 1.7E-4 Torr on new not logged cold cathode gauge. P1 <7E-4 Torr

Valve configuration: vac.normal with anunulossess closed off.

TP3 was turned off with a failing drypump. It will be replaced tomorrow.

[koji, rana, gautam]

1100 - EY chamber inspected, no issues were found --> EY heavy door on

1200 - OMC chamber was inspected. OM6 was marginally tweaked to bring the beam down a little in pitch, and also a little northwards in Yaw. --> Heavy door on.

1230 - Pumpdown started. Initially, the annuli volume was pumped down. The procedure calls for doing this with the small turbopumps. However, V7 was left open, and hence, in the process, the TP1 foreline pressure (=P2) hit ~30 torr. This caused TP1 to shutdown. We were able to restart it without issue. This case was not caught by the interlock code, which was running at the time. It should be recitified.

1330 - OMC breadboard clean optics and DCPD hardware were wrapped up and packed into tupperware boxes and stored along the south arm. OMC cavity itself, the OMMT, and the breadboard the OMC was sitting on are wrapped in foil/Ameristat and stored in cabinet S13, lower 2 shelves.

1915 - P1a = 0.5 torr pressure reached. Switched over to pumping the main volume with TP1, backed by TP2 and TP3, which themselves are backed by their respective dry pumps and also the AUX drypump for some extra oomph. All cooling fans available in the area were turned on and directed at the turbo pumps. RV2 was used to throttle the flow suitably.

It was at this point that we hit a snag - RV2 has gotten stuck in a partially open position, see Attachment #1. We can see that the thread doesn't move in response to turning the rotary dial. Fortunately, the valve is partially open, so the main volume continues to be pumped - see Attachment #2 for the full history of today's pumping. We are leaving the main volume pumped in this configuration overnight (TP1 pumping main volume backed by TPs 2 and 3, which are in turn backed by their respective drypumps and also the AUX dry pump). I think there is little to no risk of any damage to the turbo pumps, the interlocks should catch any anomalies. The roughing pumps RP1 and RP3 were turned off and that line was disconnected and capped.

What are our options?

1. The main volume is able to reach the "nominal" pressure of 1e-5 torr, just takes longer.
2. At some point, we may be able to pump the main volume directly with TP2 and TP3 - it is unclear at this point whether it's better to have the conductance limited TP1, which has a higher pumping capacity, or have the smaller TPs 2 and 3 pump through a larger conductance. 
3. Depending on how low the ultimate pressure gets, we may be able to run the usual IFO activities until the replacement pressure gauges arrive in ~1 week, at which point we can vent the pumpspool (leaving the main volume isolated) and either repair this valve or replace it with one of the spares we have.

We need some vacuum experts to comment. Why did this happen? Is this an acceptable failure mode of the valve?

KA Ed:
2230 - P1a = 0.025 torr. The pressure is coming down with log-linear scale. x0.1 per 2.5 hours or so.

Main volume pressure as of 11:30AM 2020/11/10

Jamie and Steve

We closed ITMX and ITMY chambers and started pumping around 11am

What we did before:

1, turned off AC power  to PZT Jena HV ps

2, checked jam nut positions

3, cheched  single o-ring shims

4, closed psl out shutter

[Koji, Manasa]

We missed to check that we had the green transmitted to the PSL after flipping the SRC and PRC folding mirrors.
There is no green transmission reaching the PSL even after locking the arms to green.

We should fix this tomorrow. The BS heavy door should come off.

Steve! Do not start pump down tomorrow !

This plot shows the trend of the OL during the past several hours of roughing pumping.

The big steps at the start of the pump down is NOT due to the pumping, but is instead the "recentering" that Yuta did. Looks like he was unable to find zero on the ETMY.

Some of the rest of the drift is probably just the usual diurnal variation, but there does seem to be some relation to the pumping trend. I guess that the shift of ~0.3 in the ITMX and ITMY pitch is real and pressure related.

We need to figure out how to put the OL calibration factor into the SUS-OL screens.

Summary:

I've been plugging away at Altium prototyping the high-voltage bias idea, this is meant to be a progress update.

Details:

I need to get footprints for some of the more uncommon parts (e.g. PA95) from Rich before actually laying this out on a PCB, but in the meantime, I'd like feedback on (but not restricted to) the following:

1. The top-level diagram: this is meant to show how all this fits into the coil driver electronics chain.
   • The way I'm imagining it now, this (2U) chassis will perform the summing of the fast coil driver output to the slow bias signal using some Dsub connectors (existing slow path series resistance would simply be removed). 
   • The overall output connector (DB15) will go to the breakout board which sums in the bias voltage for the OSEM PDs and then to the satellite box.
   • The obvious flaw in summing in the two paths using a piece of conducting PCB track is that if the coil itself gets disconnected (e.g. we disconnect cable at the vacuum flange), then the full HV appears at TP3 (see pg2 of schematic). This gets divided down by the ratio of the series resistance in the fast path to slow path, but there is still the possibility of damaging the fast-path electronics. I don't know of an elegant design to protect against this.
2. Ground loops: I asked Johannes about the Acromag DACs, and apparently they are single ended. Hopefully, because the Sorensens power Acromags, and also the eurocrates, we won't have any problems with ground loops between this unit and the fast path.
3. High-voltage precautons: I think I've taken the necessary precautions in protecting against HV damage to the components / interfaced electronics using dual-diodes and TVSs, but someone more knowledgable should check this. Furthermore, I wonder if a Molex connector is the best way to bring in the +/- HV supply onto the board. I'd have liked to use an SHV connector but can't find a comaptible board-mountable connector.
4.  Choice of HV OpAmp: I've chosen to stick with the PA95, but I think the PA91 has the same footprint so this shouldn't be a big deal.
5.  Power regulation: I've adapted the power regulation scheme Rich used in D1600122 - note that the HV supply voltage doesn't undergo any regulation on the board, though there are decoupling caps close to the power pins of the PA95. Since the PA95 is inside a feedback loop, the PSRR should not be an issue, but I'll confirm with LTspice model anyways just in case.
6. Cost: 
   • ​​Each of the metal film resistors that Rich recommended costs ~$15.
   • The voltage rating on these demand that we have 6 per channel, and if this works well, we need to make this board for 4 optics.
   • The PA95 is ~$150 each, and presumably the high voltage handling resistors and capacitors won't be cheap.
   • Steve will update about his HV supply investigations (on a secure platform, NOT the elog), but it looks like even switching supplies cost north of $1200.
   • However, as I will detail in a separate elog, my modeling suggests that among the various technical noises I've modeled so far, coil driver noise is still the largest contribution which actually seems to exceed the unsqueezed shot noise of ~ 8e-19 m/rtHz for 1W input power and PRG 40 with 20ppm RT arm losses, by a smidge (~9e-19 m/rtHz, once we take into account the fast and slow path noises, and the fact that we are not exactly Johnson noise limited).

I also don't have a good idea of what the PCB layer structure (2 layers? 3 layers? or more?) should be for this kind of circuit, I'll try and get some input from Rich.

*Updated with current noise (Attachment #2) at the output for this topology of series resistance of 25 kohm in this path. Modeling was done (in LTspice) with a noiseless 25kohm resistor, and then I included the Johnson noise contribution of the 25k in quadrature. For this choice, we are below 1pA/rtHz from this path in the band we care about. I've also tried to estimate (Attachment #3) the contribution due to (assumed flat in ASD) ripple in the HV power supply (i.e. voltage rails of the PA95) to the output current noise, seems totally negligible for any reasonable power supply spec I've seen, switching or linear.

Tonight I built a simpler version of what will be the new general-purpose precision temperature controller. This one is built on a breadboard and will be used for RFAM testing at the 40m until a better version is made. Some  differences between this version and the final one:

• In the interest of time, this controller senses temperature using a DC wheatstone bridge, instead of the audio-frequency bridge of the final controller.
• I eschewed the more complicated transistor current source in favor of a simple current buffer. In effect, using a constant-current source is not absolutely necessary, since we are not interested in constant current but rather a constant system temperature. In this sense, it doesn't matter if we have a transistor current source or a transistor voltage source or a current-buffered op amp voltage source; the loop will simply drive the heater with the proper current to keep the error signal nulled. 

So, how it works:

1. The DC bridge drive voltage is supplied by a voltage-divided and buffered AD587 (low-noise 10-V reference).
2. The reference resistors are just 1% metal film leaded resistors, but I have put some effort into making them quiet:
   1. Each resistor's body is wrapped in Al tape, and then all the resistors are taped together using Al tape, as well. This is to strongly couple them to each other thermally.
   2. All the reference resistors are embedded in some foam I found in the Bridge sub-B hallway. It's nothing fancy, but it keeps large advection currents from causing thermal drifts.
3. The sensing element is a PT100 100-ohm RTD. Tempco is ~0.0037 1/K
4. The bridge differential voltage is read out by an AD620 instrumentation amplifier with G = 100
5. The AD620 output is fed directly to an OP27 with G = 0-20
6. This is fed to an LF356 (FET-input op amp, to reduce the effects of bias current when the integrator is on) with a single pole at 0.1 Hz, switchable via jumper to DC for true integration
7. This is summed with an offset via an OP27 summer (the offset determines the heater current with no signal---half the maximum current of ~120 mA is optimal)
8. The summer output is buffered with a BUF634, which can provide well over the maximum current we can push through our heater, and the BUF634 directly drives the heater
9. Between the BUF634 and the heater is a back-biased diode to ground. This is to prevent the current from going negative when the error signal is well below zero.

I have tested the circuit using a spare resistive heater and a potentiometer to simulate the RTD. First I tested the sensing and drive circuits separately, then I connected the sensor output to the drive input and modulated the potentiometer resistance while monitoring the current. The circuit behaved as expected.

When I got to the 40m, it struck me that the resistance I had chosen (115 ohms) corresponded to 40 C, which I realized might be above what we could reach with the current we can provide. I used the Newport 6000 via telnet to drive the heater at several current values and see what the resistance became. I found that with I = Imax/2 ~ 0.6, the resistance was around 113 ohms (it was ~111 at room temp). So, I switched the reference resistor in the leg above the PT100 from 115 -> 113.

I then plugged everything in while monitoring the heater current and AD620 output (error signal), and it seemed not to do anything. I was tired so I figured I'd leave it for tomorrow.

Here is a sketch of the schematic, as well as some pictures:

A prototype freq divider has been made which works up to ~40MHz.

74HC4060 (14bit binary ripple counter) divides the freq of the input signal, which is comverted by the comparator LT1016
into the rectangular signal. The division rate is 2^14.

Attachment1: Circuit diagram

Attachment2: Photo, the prototype bread board

Attachment3: Photo, the spectrum of the freq divided output. The 40MHz input has been divided into 2.4k.
There are the 3rd and 5th harmonics seen. The peak was pretty sharp but the phase noise was not evaluated yet.

The circuit was made on the prototype bread board which is apparently unsuitable for RF purposes.
Indeed, it was surprising to see its working up to 40MHz...

In order to increase the maximum freq of the system we need the following considerations

• RF PCB board
• Input RF buffer (or amplifier) with a 50Ohm input impedance.
• Faster comparator. LT1016 has the response time of 10ns, which is not enough fast.
• Faster counter. Faster chip 74HC4020 has already been ordered.

I have implemented a proto-ASC in the ASS model.  

In an ASC block within the ASS model, I take in the POP QPD yaw, pit, and sum signals.  I ground the sum, since I don't have normalization yet (also, the QPD that we're using normalizes in the readout box already).  The pit and yaw signals each go through a filter bank, and then leave the sub-block so I can send the signals over to the SUS model, to push on PRM ASCPIT and ASCYAW. 

In doing this, I have removed the temporary PRM ASCYAW connection that Koji had made from the secret 11'th row of the LSC output matrix (see Koji's elog 8562 for details from when he implemented this stuff).

LSC, SUS and ASS were recompiled, and restarted.  I also restarted the daqd on the fb.

I am working on making the Proto-ASC less "proto".  I have put IPC senders in the LSC model to send the cavity trigger signals over to the ASS model, for ASC use.  I'm partially done working on the ASC end of things to implement triggering.

LSC should be compile-able right now, ASS is definitely not.  But, I expect that no one should need to compile either before I get back in a few hours.  If you do - call me and we'll figure out a plan.

I have finished my work on the LSC and ASS models for now. The triggering is all implemented, and should be ready to go.  There are no screens yet.

I have *not* compiled either the LSC or the ASS, since Rana and Manasa still have the IFO.

The proto-ASC now includes triggering.  I have updated the hacky temp ASC screen to show the DoF triggering.  I have to go, but when I get back, I'll also expose the filter module triggering.  So, for now we may still need the up/down scripts, but at least the ASC will turn itself off if there is a lockloss.

Today I implemented protection of the vac system against extended power losses. Previously, the vac controls system (both old and new) could not communicate with the APC Smart-UPS 2200 providing backup power. This was not an issue for short glitches, but for extended outages the system had no way of knowing it was running on dwindling reserve power. An intelligent system should sense the outage and put the IFO into a controlled shutdown, before the batteries are fully drained.

What enabled this was a workaround Gautam and I found for communicating with the UPS serially. Although the UPS has a serial port, neither the connector pinout nor the low-level command protocol are released by APC. The only official way to communicate with the UPS is through their high-level PowerChute software. However, we did find "unofficial" documentation of APC's protocol. Using this information, I was able to interface the the UPS to the IOLAN serial device server. This allowed the UPS status to be queried using the same Python/TCP sockets model as all the other serial devices (gauges, pumps, etc.). I created a new service called "serial_UPS.service" to persistently run this Python process like the others. I added a new EPICS channel "C1:Vac-UPS_status" which is updated by this process.

With all this in place, I added new logic to the interlock.py code which closes all valves and stops all pumps in the event of a power failure. To be conservative, this interlock is also tripped when the communications link with the UPS is disconnected (i.e., when the power state becomes unknown). I tested the new conditions against both communication failure (by disconnecting the serial cable) and power failure (by pressing the "Test" button on the UPS front panel). This protects TP2 and TP3. However, I discovered that TP1---the pump that might be most damaged by a sudden power failure---is not on the UPS. It's plugged directly into a 240V outlet along the wall. This is because the current UPS doesn't have any 240V sockets. I'd recommend we get one that can handle all the turbo pumps.

For future reference:

Pin 1: RxD

Pin 2: TxD

Pin 5: GND

Standard: RS-232

Baud rate: 2400

Data bits: 8

Parity: none

Stop bits: 1

Handshaking: none

agreed - we need all pumps on UPS for their safety and also so that we can spin them down safely. Can you and Chub please find a suitable UPS?

Problem:

The controls (fast and slow both) think ITMX is ITMY and ITMY is ITMX.

Solution:

After some poking around today, I have convinced myself it is sufficient to simply swap all instances of ITMX for ITMY in the C1_SUS-AUX1_ITMX.db  file, and then rename it to C1_SUS-AUX1_ITMY.db (after having moved the original C1_SUS-AUX1_ITMY.db to a temporary holding file).

A similar process is then applied to the original C1_SUS-AUX1_ITMY.db file.  These files live in /cvs/cds/caltech/target/c1susaux.  This will fix all the slow controls.

To fix the fast controls, we'll modify the c1sus.mdl file located in /opt/rtcds/caltech/c1/core/advLigoRTS/src/epics/simLink/ so that the ITMX suspension name is changed to ITMY and vice versa.  We'll also need to clean up some of the labeling

At Kiwamu and Bryan's request, this will either be done tomorrow morning or on Monday.

So the steps in order are:

1) cd /cvs/cds/caltech/target/c1susaux

2) mv C1_SUS-AUX1_ITMX.db C1_SUS-AUX1_ITMX.db.20110408

3) mv C1_SUS-AUX1_ITMY.db C1_SUS-AUX1_ITMY.db.20110408

4) sed 's/ITMX/ITMY/g' C1_SUS-AUX1_ITMX.db.20110408 > C1_SUS-AUX1_ITMY.db

5) sed 's/ITMY/ITMX/g' C1_SUS-AUX1_ITMY.db.20110408 > C1_SUS-AUX1_ITMX.db

6) models

7) matlab

8) Modify c1sus model to swap ITMX and ITMY names while preserving wiring from ADCs/DACs/BO to and from those blocks.

9) code; make c1sus; make install-c1sus

10) Disable all watchdogs

11) Restart the c1susaux computer and the c1sus computer

Here' s aquick update before we leave for lunch. We have managed to calculate some filter that would go on the POS column in MC2 output matrix filter banks aka F2A aka F2P filters. In the afternoon if we can come and work on the IMC, we'll try to load them on the output matrix. We have never done that so it might take some time for us to understand on how to do that. Attached is the bode plot for these proposed filters. Let us know if you have any comments.

Motivation: I want to make another measurement of the out-of-loop ALS beat noise, with improved MM into both the PSL and EX fibers and also better polarization control. For this, I want to make a few changes at the EX table. 

1. Replace existing fiber collimator with one of the recently acquired F220-APC-1064 collimators.
   • This gives an output mode of diameter 2.4mm with a beam divergence angle of 0.032 degrees (all numbers theoretical - I will measure these eventually but we need a beam path of ~5m length in order to get a good measurement of this collimated beam).
   • I believe it will be easier to achieve good mode matching into this mode rather than with the existing collimator. 
   • Unfortunately, the mount is still going to be K6X and not K6XS. 
2. Improve mode-matching into fiber.
   • I used my measurement of the Innolight NPRO mode from 2016, a list of available lenses, and some measured distances to calculate a solution that gives theoretical 100% overlap with the collimator mode, that has beam diameter 2.4mm, located 80cm from the NPRO shutter head location (see Attachment #1).
   • The required movement of components is schematically illustrated in Attachment #2.
   • One of the required lens positions is close to the bracket holding the enclosure to the table, but I think the solution is still workable (the table is pretty crowded so I didn't bother too much with trying to find alternative solutions as all of them are likely to require optics placed close to existing ones and I'd like to avoid messing with the main green beam paths.
   • I will attempt to implement this and see how much mode matching we actually end up getting.
3. Install a PBS + HWP combo in the EX fiber coupling path.
   • This is for better polarization control.
   • Also gives us more control over how much light is coupled into the fiber in a better way than with the ND filters in current path.
4. Clean EX fiber tip.
5. Dump a leakage IR beam from the harmonic separator post doubling oven, which is currently just hitting the enclosure. It looks pretty low power but I didn't measure it.
6. Re-install EX power monitoring PD.

Barring objections, I will start working on these changes later today.

I started working on the EX table. Work is ongoing so I will finish this up later in the evening, but in case anyone is wondering why there is no green light...

1. EX laser shutter was closed.
2. Disconnected EX input to the beat mouth at the PSL table in order to avoid accidentally frying the PDs.
3. Prepared new optomechanics hardware
   • To my surprise, I found a bubble-wrapped K6XS mount (the one with locking screws for all DoFs) on the SP table. No idea where this came from or who brought it here, or how long it has been here, but I decided to use it nevertheless.
   • Prepared f = 200mm and f = -200mm lenses on traveling mounts (Thorlabs DT12, lenses are also Thorlabs, AR1064).
   • Made a slight translation of the beam path towards the north to facilitate going through the center of the mounted lenses.
   • Temporarily removed a beam dump from next to the final steering mirror before the Green REFL PD, and also removed one of the brackets between the enclosure and the table for ease of laying out components. These will be replaced later.
4. Installed this hardware on the PSL table, roughly aligned beam path.
   • Beam now goes through the center of all lenses and is hitting the collimator roughly in the center.

To do in the eve:

1. Clean fiber and connect it to the collimator.
2. Optimize mode-matching as best as possible.
3. Attenuate power using PBS and HWP so as to not damage the BeatMouth PD (Pthresh = 2mW). These are also required to make the polarizations of the EX coupled light (S-pol) and PSL (P-pol) go along the same axis of the PM fiber.
4. Re-install temporarily removed beam dump and bracket on EX table.
5. Re-install EX power monitoring PD.
6. Measure beat frequency spectrum.

gautam 1245am: Fiber cleaning was done - I'll upload pics tomorrow, but it seems like the fiber was in need of a good cleaning. I did some initial mode-matching attempts, but peaked at 10% MM. Koji suggested not going for the final precisely tunable lens mounting solution while trying to perfect the MM. So I'll use easier to move mounts for the initial tuning and then swap out the DT12s once I have achieved good MM. Note that without any attenuation optics in place, 24.81mW of power is incident on the collimator. In order to facilitate easy debugging, I have connected the spare fiber from PSL to EX at the PSL table to the main EX fiber - this allows me to continuously monitor the power coupled into the fiber at the EX table while I tweak lens positions and alignment. After a bit of struggle, I noticed I had neglected a f=150mm lens in my earlier calculation - I've now included it again, and happily, there seems to be a solution which yields the theoretical 100% MM efficiency. I'll work on implementing this tomorrow..

I am currently working on an optical arrangement consisting of a QPD that measures the fluctuations of an incoming HeNe laser beam that is reflected by a mirror. The goal is to add a second QPD to the optical arrangement to form a linear combination that effectively cancels out the (angular) fluctuations from the laser beam itself so that we can only focus on the fluctuations produced by the mirror.

In order to solve this problem, I have written a program for calculating the different contributions of the fluctuations of the HeNe laser and fluctuations from the mirror, for each QPD (program script attached). The goal of the program is to find the optimal combination of L0, L1, L2, and f2 that cancels the fluctuations from the laser beam (while retaining  solely the fluctuations from the mirror) when adding the fluctuations of QPD 1 and QPD 2 together. 

By running this program for different combinations of distances and focal lengths, I have found that the following values should work to cancel out the effects of the oscillations from the HeNe laser beam (assuming a focal length of 0.2 m for the lens in front of the original QPD):

• L0 = 1.0000 m (distance from laser tube to mirror)

• L1 = 0.8510 m (distance from mirror to lens in front of QPD 1)

• L2 = 0.9319 m (distance from beamsplitter to lens in front of QPD 2)

• f2 = 0.3011 m (focal length of lens in front of QPD 2)

Based on these calculations, I propose to try the following lens for QPD 2:

1’’ UV Fused Silica Plano-Convex Lens, AR-Coated: 350 - 700 nm (focal length 0.3011 m). https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=6508

I have mounted 2 2" G&H high reflective mirrors, to be used in the new POP path.  Manasa and Annalisa are doing green things on their respective arms, so I will hopefully be able to install the new POP path after dinner tonight.

Here are photos of the current POP path, and my proposed POP layout.  In the proposed layout, the optical components whose labels are shaded are the ones which will change.

Attachment #1 is a sketch of the proposed setup to measure the PM response of the EX NPRO. Previously, this measurement was done via PLL. In this approach, we will need to calibrate the DFD output into units of phase, in order to calibrate the transfer function measurement into rad/V. The idea is to repeat the same measurement technique used for the AM - take ~50 1 average measurements with the AG4395, and look at the statistics. 

Some more notes:

• Delay line box is passive, just contains a length of cable.
• IQ Demodulation is done using an aLIGO 1U chassis unit, with the actual demod board electronics being D0902745
• The RF beatnote amplitude out of the IR beat PD is ~ -8dBm.
• The ZHL-3A amplifiers have gain of 24dB, so the amplified beat should be ~16dBm
• At the LSC rack, the amplified beat is split into two - one path goes to the LO input of D0902745 (so at most 13dBm), the other goes through the delay line.
• On the demod board, the LO signal is amplified with a AP1053, rated at 10dB gain, max output of 26dBm, so the signal levels should be fine for us, even though the schematic says the nominal LO level is 10dBm - moreover, I've ignored cable losses, insertion losses etc so we should be well within spec.
• The mixer is PE4140. The datasheet quotes LO levels of 17dBm for all the "nominal" tests, we should be within a couple of dBm of this number.
• There is no maximum value specified for the RF input signal level to the mixer on the datasheet, but I expect it to be <10dBm.
• We should park the beatnote around 30MHz as this should be well within the operational ranges for the various components in the signal chain.

 After familiarizing myself with Altium, I drew up the attached schematic for the ISS to be used in the CTN experiment. The filename includes 'abbott-switch' as I am using an Altium component (the switch, in particular), that he created. The MAX333A actually has 20 pins on a single component, but the distributed component that he created is useful for drawing uncluttered schematics. I won't be using all of the pins on this switch, but for completeness, I have included the 3rd and 4th portion of the full component in the upper right hand corner.

Currently, the schematic includes the voltage reference (AD586), a LP filter for the reference signal, the differential amplifier stage to obtain the error signal and then finally all of the filter stages. The schematic does not include the RMS detection and subsequent triggering of each filter stage. The TRIGGER 1 signal is a user input (essentially the on button) while the TRIGGER 2 signal will flip the second switch when the RMS noise has decreased sufficiently after the first filter stage has been turned on. 

PCB layouts will be done once I understand that part of Altium 

NOTE THAT I HAVE DELETED ELOG 8798 AS IT WAS A DUPLICATE OF THIS ONE.

I wanted this elog to be in reply to a previous one and I couldn't figure out how to change that in an elog I already submitted.

Following Tara's noise budget, I have developed the following ISS, whose transfer function was computed with LISO and is also displayed below. The transfer function was computed from the output of the differential amplifier circuit (i.e. it does not include the portion of the schematic in the dashed box). The differential amplifier is included for completeness. Essentially, the resistor values of this portion (and even the voltage reference if need be) can be modified to handle various signals from PDs in different experiments. Some filtering may also be applied to the signal from the voltage reference. In previous designs for the ISS, a ~30 mHz low-pass filter applied to the output of the voltage reference has also been proposed.

LISO was also used to compute the input-referred noise of this circuit. Using the response function of Tara's PD the noise spectrum was converted from [V / sqrt(Hz)] to [W / sqrt(Hz)] and then subsequently converted to a frequency noise spectrum, specifically [W / sqrt(Hz)] to [Hz / sqrt(Hz)], using the following transfer function which couples RIN to frequency noise in the CTN experiment. In these particular units, we can make a direct comparison between the inherent noise contribution from the servo itself and other more significant noise contributions shown earlier in Tara's noise budget. Indeed, the servo contributes significantly less noise.

This servo has been prototyped on a breadboard and will soon be characterized with the SR785. Additionally, schematics will be drawn up in Altium and eventually put on PCB.

Additional servos for other experiments can be designed once various requirements for noise suppression are explicitly formalized.

I've been developing an idea for making a direct measurement of the SRC Gouy phase at RF. It's a very different approach from what has been tried before. Prior to attempting this at the sites, I'm interested in making a proof-of-concept measurement demonstrating the technique on the 40m. The finesse of the 40m SRC will be slightly higher than at the sites due to its lower-transmission SRM. Thus if this technique does not work at the 40m, it almost certainly will not work at the sites.

The idea is, with the IFO locked in a signal-recycled Michelson configuration (PRM and both ETMs misaligned), to inject an auxiliary laser from the AS port and measure its reflection from the SRC using one of the pre-OMC pickoff RFPDs. At the sites, this auxiliary beam is provided by the newly-installed squeezer laser. Prior to injection, an AM sideband is imprinted on the auxiliary beam using an AOM and polarizer. The sinusoidal AOM drive signal is provided by a network analyzer, which sweeps in frequency across the MHz band and demodulates the PD signal in-phase to make an RF transfer function measurement. At the FSR, there will be a AM transmission resonance (reflection minimum). If HOMs are also present (created by either partially occluding or misaligning the injection beam), they too will generate transmission resonances, but at a frequency shift proportional to the Gouy phase. For the theoretical 19 deg one-way Gouy phase at the sites, this mode spacing is approximately 300 kHz. If the transmission resonances of two or more modes can be simultaneously measured, their frequency separation will provide a direct measurement of the SRC Gouy phase.

The above figure illustrates this measurement configuration. An attached PDF gives more detail and the expected response based on Finesse modeling of this IFO configuration.

Summary:

I set up a free-space beat on theNW side of the PSL table between the IR beam from the PSL and from EX, the latter brought to the PSL table via ~40m fiber. Initial measurements suggest very good performance, although further tests are required to be sure. Specifically, the noise below 10 Hz seems much improved.

Details:

Attachment #1 shows the optical setup. 

• I used two identical Thorlabs F220APC collimators to couple the light back into free space, reasoning that the mode-matching would be easiest this way.
• Only 1 spare K6Xs collimator mount was available (this has the locking nut on the rotational DoF), so I used a K6X for the other mount. The fast axis of the Panda fibers were aligned as best as possible to p-polarization on the table by using the fact that the connector key is aligned to the slow axis.
• I cut the power coupled into the PSL fiber from ~2.6mW to ~880uW (using a HWP + PBS combo before the input coupling to the fiber) to match the power from EX.
• The expected signal level from these powers and the NF1611 transimpedance of 700 V/A is ~320 mVpp. After alignment tweaking, I measured ~310mVpp (~ -5dBm) into a 50 ohm input on a scope, so the mode-matching which means the polarization matching and mode overlap between the PSL and EX beams are nearly optimal.
• To pipe the signal to the delay line electronics, I decided to use the ZHL-3A (G=27dB, 1dB compression at 29.5dBm per spec), so the signal level at the DFD rack was expected (and confirmed via 50 ohm input on o'scope) to be ~19dBm.
• This is a lot of signal - after the insertion loss of the power splitter, there would still be ~15dBm of signal going to the (nominally 10dBm) LO input of the demod board. This path has a Teledyne AP1053 at the input, which has 10dB gain and 1dBm compression at 26dBm per spec. To give a bit of headroom, I opted on the hacky solution of inserting an attenuator (5dB) in this path - a better solution needs to be implemented.
• The differential outputs of the demod board go to the CDS system via an AA board (there is no analog whitening).

Yehonathan came by today so I had to re-align the arms and recover POX/POY locking. This alllowed me to lock the X arm length to the PSL frequency, and lock the EX green laser to the X arm length. GTRX was ~0.36, whereas I know it can be as high as 0.5, so there is definitely room to improve the EX frequency noise suppression.

Attachment #2 shows the ALS out-of-loop noise for the PSL+X combo. The main improvements compared to this time last year are electronic. 

• The failed experiment of making custom I/F amplifier was abandoned and Rich Abbott's original design was reverted to. 
• New power splitter was installed with 3dB less insertion loss.
• According to the RF path level monitor, the signal level at the RF input to the demod board is ~10dBm. Per my earlier characterization, this will give us the pretty beefy frequency discriminant of ~15uV/Hz.
• I estimate the frequency noise of the detection electronics + ADC noise now translate to 1/3 the frequency noise compared to the old system. With some analog whitening, this can be made even better, the electronics noise of the DFD electronics (~50nV/rtHz) is estimated to be <10mHz/rtHz equivalent frequency noise. 
• Note that the calibration from phase-tracker-servo to units of Hz (~14 kHz / degree) was not changed in the digital system - this should only be a property of the delay line length, and hence, should not have changed as a result of the various electronics changes to the demod board and other electronics.

Next steps:

• Improve pointing of green beam into X arm cavity.
• I plan to recover the green beat note as well and digitize it using the second available DFD channel (eventually for the Y arm) - then we can simultaneously compare the the green and IR performance (though they will have different noise floors as there is less green light on the green beat PDs, and I think lower transimpedance too).

I noticed this behaviour since ~Dec 20th, before the power failure. The bulb itself seems to work fine, but the projector turns itself off after <1 minute after being manually turned on by the power button. AFAIK, there was no changes made to the projector/Zita. Perhaps this is some kind of in-built mechanism that is signalling that the bulb is at the end of its lifetime? It has been ~4.5 months (3240 hours) since the last bulb replacement (according to the little sticker on the back which says the last bulb replacement was on 15 Aug 2017

Koji, Gautam, Johannes

We quickly checked the situation of the projector in the control room.

- We found that the proejctor was indicating "lamp error".
==> Steve, could you remove the projector from the ceiling and check if it still does not work?
If it still does not work, send it back to the vender. It should be covered by the previous service.

- Zita seemed happy with the DVI output. We tried the dual display configration and  VGA and DVI are active right now.
The DVI output (from RADEON something video card) is somewhat strange. We probably need to look into the video display situation.

Last documented replacement in Nov 2018, so ~7 months, which I believe is par for the course. I am disconnecting its power supply cable.

In fact the projector is still working. The lamp timer showed ~8200hrs. I just reset the timer, but not sure it was the cause of the shutdown. I also set the fan mode to be "High Altitude" to help cooling.

I heard a popping sound in the control room; the projector lightbulb has blown out.

[chub, gautam]

Bulb replaced. Projector is back on.

Projector light bulb blown out today.

This bulb was blown out on Feb 4, 2017 after 2 months of operation.

Three replacement bulbs ordered

Rana can discribe how it happened.

IF A LAMP EXPLODES

Shipped out for repair.

It is back and running fine witth bulb  4-13-2017

I replaced the projector video and power cables with longer ones, and zip-tied them to the ceiling and wall so they don't block the image.

Update: We don't have our BIG screen 

There was no light from the projector when I came in this morning. I suspected it might have to do with the lifetime of the bulb. But turning the projector OFF and ON got the projector working....but only for about 10-15 seconds. The display would go OFF after that. I will wait for some additional help to dismount it and check what the problem really is.