It was indeed the issue of the top OSEM plate not being in the right place horizontally. But the issue was more non-trivial. I believe because of the wedge in thick optics, there is a YAW offset in the optic in the free hanging position. I had to readjust the OSEM plate 4 times to be able to get full dark to bright range in both upper OSEMs. After doing that, I tuned the four OSEMs somewhat near the halfway point and once I was sure I'm inside the sensitive region in all face OSEMs, I switched on POS, PIT, and YAW damping. Then I was able to finely tune the positions of both upper OSEMs.
However, on reaching to lower right OSEM, I found again the same issue. I had to stop to go to the 40m meeting, I'll continue this work in the afternoon. But OSEM plate adjustment in the horizontal direction, particularly for thick optics is required to be done before transporting them. I achieved the best position by turning the OSEM 90 degrees and using the OSEM LED/PD plates to determine the position. This was the final successful trial I did in adjusting the plate position horizontally.
[Paco, Tega, Anchal]
Today, we started work on AS4 SOS by checking the OSEM and cable. Swapping the connection preserved the failure (no counts) so we swapped the long OSEM for a short one that we knew was working instead, and this solved the issue. We proceeded to swap in a "yellow label", long OSEM in place and then noticed the top plate had issues with the OSEM threads. We took out the bolt and inspected its thread, and even borrowed the screw from PR2 plate but saw the same effect. Even using a silver plated setscrew such as the SD OSEM one resulted in trouble... Then, we decided to not keep trying weird things, and took our sweet time to remove the UL, UR OSEMs, top earthquake stops, and top plate carefully in-situ. Then, we continued the surgery by installing a new top plate which we borrowed from the clean room (the only difference is the OSEM aperture barrels are teflon (?) rather than stainless. The operation was a success, and we moved on to OSEM installation.
After reaching a good place with the OSEM installation, where most sensors were at 50% brightness level and we were happy with the damping action (!!), we fixed all EQ stops and proceeded to push the SOS to its nominal placement. Then upong releasing the EQ stops, we found out that the sensor readings were shifted.
Is this the correct status? Please directly update this entry.
LO1 [Glued] [Suspended] [Balanced] [Placed In Vacuum] [OSEM Tuned] [Damped]
LO2 [Glued] [Suspended] [Balanced] [Placed In Vacuum] [OSEM Tuned] [Damped]
AS1 [Glued] [Suspended] [Balanced] [Placed In Vacuum] [OSEM Tuned] [Damped]
AS4 [Glued] [Suspended] [Balanced] [Placed In Vacuum] [OSEM Tuned] [Damped]
PR2 [Glued] [Suspended] [Balanced] [Placed In Vacuum] [OSEM Tuned] [Damped]
PR3 [Glued] [Suspended] [Balanced] [Placed In Vacuum] [OSEM Tuned] [Damped]
SR2 [Glued] [Suspended] [Balanced] [Placed In Vacuum] [OSEM Tuned] [Damped]
I have further updated my calculation. Please find the results in the attached pdf.
Following is the description of calculations done:
Reflection fro arm cavity is calculated as simple FP cavity reflection formula while absorbing all round trip cavity scattering losses (between 50 ppm to 200 ppm) into the ETM transmission loss.
So effective reflection of ETM is calculated as
The magnitude and phase of this reflection is plotted in page 1 with respect to different round trip loss and deviation of cavity length from resonance. Note that the arm round trip loss does not affect the sign of the reflection from cavity, at least in the range of values taken here.
The Michelson in PRFPMI is assumed to be perfectly aligned so that one end of PRC cavity is taken as the arm cavity reflection calculated above at resonance. The other end of the cavity is calculated as a single mirror of effective transmission that of PRM, 2 times PR2 and 2 times PR3. Then effective reflectivity of PRM is calculated as:
Note, that field transmission of PRM is calculated with original PRM power transmission value, so that the PR2, PR3 transmission losses do not increase field transmission of PRM in our calculations. Then the field gain is calculated inside the PRC using the following:
From this, the power recycling cavity gain is calculated as:
The variation of PRC Gain is showed on page 2 wrt arm cavity round trip losses and PR2 transmission. Note that gain value of 40 is calculated for any PR2 transmission below 1000 ppm. The black verticle lines show the optics whose transmission was measured. If V6-704 is used, PRC Gain would vary between 15 and 10 depending on the arm cavity losses. With pre-2010 ITM, PRC Gain would vary between 30 and 15.
LO power when PRFPMI is locked is calculated by assuming 1 W of input power to IMC. IMC is assumed to let pass 10% of the power (). This power is then multiplied by PRC Gain and transmitted through the PR2 to calculate the LO power.
Page 3 shows the result of this calculation. Note for V6-704, LO power would be between 35mW and 15 mW, for pre-2010 ITM, it would be between 15 mW and 5 mW depending on the arm cavity losses.
The power available during alignment is simply given by:
If we remove PRM from the input path, we would have sufficient light to work with for both relevant optics.
I have attached the notebook used to do these calculations. Please let me know if you find any mistake in this calculation.
Today I suspended AS1. Anchal helped me with the initial hanging of the optics. Attachments 1,2 show the roll balance and side magnet height. Attachment 3 shows the motion spectra.
The major peaks are at 668mHz, 821mHz, 985mHz.
For some reason, I was not able to balance the pitch with 2 counterweights as I did with the rest of the thin optics (and AS1 before). Inserting the weights all the way was not enough to bring the reflection up to the iris aperture that was used for preliminary balancing. I was able to do so with a single counterweight (attachment 4). I'm afraid something is wrong here but couldn't find anything obvious. It is also worth noting that the yaw resonance 668mHz is different from the 755mHz we got in all the other optics. Maybe one or more of the wires are not clamped correctly on the side blocks?
The OSEMs were pushed into the OSEM plate and the plates were adjusted such that the magnets are at the center of the face OSEMs. The wires were clamped and cut from the winches. The SOS is ready for installation.
Also, I added a link to the OSEM assignments spreadsheet to the suspension wiki.
I uploaded some pictures of the PEEK EQ stops, both on the thick and thin optics, to the Google Photos account.
After some work on the reference database file, we now have a template for temporary watchdog implementation for LO1 located here "/cvs/cds/caltech/target/c1susaux/C1_SUS-AUX_LO1.db".
Basically, what I have done is swap the EPICS asyn analog input readout for the COIL and OSEM to accessible medm channels, then write out watchdog enable/disable to coil filter SW2 switch. Everything else in the file remains the same. I am worried about some of the conversions but the only way to know more is to see the output on the medm screen.
To test, I restarted c1su2 but this did not make the LO1 database available, so I am guessing that we also need to restart the c1sus, which can be done tomorrow.
As the new db is made for c1susaux, 1) it needs to be configured to be read by c1susaux 2) it requires restarting c1susaux 3) it needs to be recorded by FB 4) and restartinbg FB.
(^-Maybe not super exact procedure but conceptually like this)
IMC is not such lossy. IMC output is supposed to be ~1W.
The critical coupling condition is G_PRC = 1/T_PRM = 17.7. If we really have L_arm = 50ppm, we will be very close to the critical coupling. Maybe we are OK if we have such condition as our testing time would be much longer in PRMI than PRFPMI at the first phase. If the arm loss turned out to be higher, we'll be saved by falling to undercoupling.
When the PRC is close to the critical coupling (like 50ppm case), we roughly have Tprc x 2 and Tarm to be almost equal. So each beam will have 1/3 of the input power i.e. ~300mW. That's probably too much even for the two OMCs (i.e. 4 DCPDs). That's OK. We can reduce the input power by 3~5.
LO power when PRFPMI is locked is calculated by assuming 1 W of input power to IMC. IMC is assumed to let pass 10% of the power ().
I was wondering whether I should take AS1 down to redo the wire clamping on the side blocks. I decided to take the OpLev spectrum again to be more certain. Attachments 1,2,3 show 3 spectra taken at different times.
They all show the same peaks 744mHz, 810mHz, 1Hz. So I think something went wrong with yesterday's measurement. I will not take AS1 down for now. We still need to apply some glue to the counterweight.