All the front ends are back up.
I found all the front-ends, except for C1SUSVME1 and C0DCU1 down this morning. DAQAWG shows up green on the C0DAQ_DETAIL screen but it is on a "bad" satus.
I'll go for a big boot fest.
I burtrestored all the snapshots to Dec 9 2009 at 18:00.
Note: The set point C1:PSL-FSS_RCPID_SETPOINT is 37.0 on C1PSL_FSS_RCPID.adl.
Now the temp is recovering with its full speed. At some point we have to restore the value of the FSS SLOW DC as the temp change drag it up.
Koji, Jenne, Rob
We found that the RCPID servo "setpoint" was not in the relevant saverestore.req file, and so when c1psl got rebooted earlier this week, this setting was left at zero. Thus, the RC got a bit chilly over the last few days. This channel has been added.
Also, RCPID channels have been added (manually) to conlog_channels.
Instead of doing RCG stuff, I went to Millikan to work on data analysis as I couldn't stand the fumes from the construction. (this morning, 8am)
Diesel fumes are pumped away from control room AC intakes with the help of newly installed reflector boxes on the CES wall fans.........see # 2272
Well, I get the point now. It could be either seismic or change in the suspension Q.
The pendulum memorizes its own state for a period of ~ Q T_pend. (T_pend is the period of the pendulum)
If the pendulum Q is very high (>104), once the pendulum is excited, the effect of the excitation can last many hours.
On the other hand, in our current case, we turned on the damping once, and then turned off the damping.
Again it takes ~Q T_pend to be excited.
In those cases, the peak height is not yet before in equilibrium, and can be higher or lower than expected.
So, my suggestion is:
Track the peak height along the long time scale (~10hrs) and compare between the previous one and the current one.
This may indicate whether it is equilibrium or not, and where the equilibrium is.
If such variation of the peak heights is cased by the seismic activity, it means the seismic level change by several 10 times. It sounds large to me.
Okay, now the data are attached. At that time I just wanted to say like the follower.
- - -
In the free-swinging spectra around ~0.5Hz, you can see the two resonances, which come from pitch and yaw mode of the pendulum.
Note that, the vertical and the horizontal axis are adjusted to be the same for the two plots in the figure .
And I found that
* the floor levels are almost the same (the factor of about 1.5 or something like that) compared to the past.
* however the peak heights for two resonances are several 10 times smaller than the past.
* this tendency are shown in all of the data (ITMX, ETMX, ETMY).
If such variation of the peak heights is cased by the seismic activity, it means the seismic level change by several 10 times. It sounds large to me.
By the way I found a trend, which can be seen in all of the data taken today and yesterday.
The resonances of pitch and yaw around 0.5Hz look like being damped, because their height from the floor become lower than the past.
I don't know what goes on, but it is interesting because you can see the trend in all of the data.
[Kiwamu, Jenne, Alberto, Steve, Bob, Koji]
We finished wiping of four test masses without any trouble. ITMY looked little bit dusty, but not as much as ITMX did.
We confirmed the surface of the ITMX again as we worked at vertex a lot today. It still looked clean.
We closed the light doors. The suspensions are left free tonight in order to check their behavior.
Tomorrow morning from 9AM, we will replace the door to the heavy ones.
Please do not touch the watchdogs for all SUSs except for MCs,
because I am going to measure the free swinging spectra for ITMs, ETMs, BS, PRM, SRM tonight.
Today, it is good chance to summarize those data under atmospheric pressure.
I finally got around to taking a look at the digital camera setup today. Rob had complained the client had stopped working on Rosalba.
After looking at the code start up and not complain, yet not produce any window output, it looks like it was a network problem. I tried rebooting Rosalba, but that didn't fix anything.
Using netstat -an, I looked for the port 5010 on both rosalba and ottavia, since that is the port that was being used by the camera. Ottavia was saying there were 6 established connections after Rosalba had rebooted (rosalba is 220.127.116.11). I can only presume 6 instances of the camera code had somehow shutdown in such a way they had not closed the connection.
[root@ottavia controls]#netstat -an | grep 5010
tcp 0 0 0.0.0.0:5010 0.0.0.0:* LISTEN
tcp 0 0 18.104.22.168:5010 22.214.171.124:57366 ESTABLISHED
tcp 0 0 126.96.36.199:5010 188.8.131.52:58417 ESTABLISHED
tcp 1 0 184.108.40.206:46459 220.127.116.11:5010 CLOSE_WAIT
tcp 0 0 18.104.22.168:5010 22.214.171.124:57211 ESTABLISHED
tcp 0 0 126.96.36.199:5010 188.8.131.52:57300 ESTABLISHED
tcp 0 0 184.108.40.206:5010 220.127.116.11:57299 ESTABLISHED
tcp 0 0 18.104.22.168:5010 22.214.171.124:57315 ESTABLISHED
I switched the code to use port 5022 which worked fine. However, I'm not sure what would have caused the original connection closure failures, as I test several close methods (including the kill command on the server end used by the medm screen), and none seemed to generate this broken connection state. I rebooted Ottavia, and this seemed to fix the connections, and allowed port 5010 to work. I also tried creating 10 connections, which all seem to run fine simultaneously. So its not someone overloading that port with too many connections which caused the problem. Its like the the port stopped working somehow, which froze the connection status, but how or why I don't know at this point.
The construction activity is shaking the tables in the control room. The compactor- large remote controlled jackhammer is in the bottom of the 16-17 ft deep hole 15 ft east of ITMY in CES bay. The suspensions are holding OK. PRM, MC1 and MC3 are effected mostly.
We like to see it if you think this is interesting.
... Just a naive guess: Is it just because the seismic level got quiet in the night?
You looks consistently confused some words like damping, Q, and peak height.
dy = H dx
As the damping makes the Q lower, the peak height also gets lowered by the damping.
But if the disturbance gets smaller, the peak height can become small even without any change of the damping and the Q.
The free swinging spectra of ETMY and ITMX were taken after today's wiping, in order to check the test masses.
These data were taken under the atmospheric pressure condition, as well as the spectra of ETMX taken yesterday.
Compared with the past (see Yoichi's good summary in Aug.7 2008), there are no significant difference.
There are nothing wrong with the ETMY and ITMX successfully.
Jenne, Kiwamu, Koji, Alberto, Steve, Bob
ITMX was wiped without having to move it.
After 'practice' this morning on ETMY, Kiwamu and I successfully wiped ITMX by leaning into the chamber to get at the front face.
Most notable (other than the not moving it) was that inspection with the fiber light before touching showed many very small particles on the coated part of the optic (this is versus ETMY, where we saw very few, but larger particles). The after-wiping fiber light inspection showed many, many fewer particles on the optical surface. I have high hopes for lower optical loss here!
Jenne, Kiwamu, Alberto, Steve, Bob, Koji
We wiped ETMY after recovery of the computer system. We take the lunch and resume at 14:00 for ITMX.
Detailed reports will follow.
Alberto, Kiwamu, Koji,
this morning we found the RFM network and all the front-ends down.
To fix the problem, we first tried a soft strategy, that is, we tried to restart CODAQCTRL and C1DCUEPICS alone, but it didn't work.
We then went for a big bootfest. We first powered off fb40m, C1DCUEPICS, CODAQCTRL, reset the RFM Network switch. Then we rebooted them in the same order in which we turned them off.
Then we power cycled and restarted all the front-ends.
Finally we restored all the burt snapshots to Monday Dec 7th at 20:00.
Opening of ETMY has been put on hold to deal with the computer situation. Currently all front end computers are down. The DAQ AWGs are flashing green, but everything else is red (fb40m is also green). Anyhow, we'll deal with this, and open ETMY as soon as we can.
The computers take priority because we need them to tell us how the optics are doing while we're in the chambers, fitzing around. We need to be sure we're not overly kicking up the suspensions.
In this night, I checked the free swinging spectra of ETMX to make sure nothing wrong with ETMX by the wiping.
Compared with the past (Aug.6 2008), the spectra of ETMX doesn't show significant change.
Successfully the wiping activity didn't change its configuration so much and didn't bring bad situations.
(bad situation means for example, the suspended components hit some others).
The spectra of ETMX by DTT are attached. Also you can see the past spectra in Yoichi's entry.
Yoichi's data was taken during the air-pressure condition, so it's good for comparing.
Actually I compared those data by my eyes, because I could not get the past raw data somehow.
The resonant frequencies and their typical height changed a little bit, but I think those are not significant.
NOTE: In the figure, pitch and yaw modes (~0.57Hz and ~0.58Hz) look like having a smaller Q-factor than the past.
I have made some measurements of the R value for some coatings we are interested in. The plots have statistical error bars from repeated measurements, but I would suspect that these do not dominate the noise, and would guess these should be trusted to plus or minus 5% or so. They still should give some indication of how useful these coatings will be for the green light. I plan to measure for the ITM as soon as possible, but with the venting and finals this may not be until late this week.
EDIT (12/9/09): I fixed the label on the y axis of the plots, and changed them to png format.
[Koji, Jenne, Alberto, Steve, Bob]
ETMX has been drag wiped.
Around 2:45pm, after the main IFO volume had come up to atmospheric pressure, we removed both doors to the ETMX chamber. Regular procedures (wiping of O-rings with a dry, lint-free cloth, covering them with the light O-ring covers, etc.) were followed. Koji took several photos of the optic, and the rest of the ETMX chamber before anything was touched. These will be posted to the 40m Picasa page. Steve and Koji then deionized the optic.
Koji removed the bottom front earthquake stop, and clamped the optic with the remaining earthquake stops.
The clean syringes were prepared: These are all glass and metal (nothing else) medical syringes. The size used was 100microliters. Earlier today, we had prepared our solvents in small little beakers which had been baked over the weekend. Brand new glass bottles of Acetone and Isopropyl Alcohol were opened, and poured into the small beakers. To make sure we have enough, we have 3 ~10ml beakers of each Acetone and Isopropyl.
We started with Acetone. The syringe was filled completely with acetone, then squirted onto a kimwipe. This was repeated ~twice, to ensure the syringe was well rinsed. Then the syringe was filled a little past the 100 microliter mark. Koji held a piece of lens cleaning paper to ETMX and used an allen wrench underneath the optic to help guide the paper, and keep it near the optic (of course, the only thing in actual contact with the optic was the lens paper). In one smooth shot, the plunger of the syringe was pressed all the way down. (This is a bit tricky, especially when the syringe is totally full. You have to squeeze it so the plunger moves fairly quickly down the barrel of the syringe to get a good arc of liquid. The goal is to shoot all of the solvent to the same place on the lens paper, so that it makes a little circle of wetness on the paper which covers the coated part of the optic. The amount of solvent used should be balanced between having too little, so that the paper is dry by the time it has been wiped all the way down, and too much such that there is still a residue of liquid on the optic after the paper has been removed.) The target was to hit the optic just above the center mark (the oplev was on, so I went for just above the red oplev dot). Immediately after applying the liquid onto the paper, Koji slowly and smoothly pulled down on the lens paper until it came off of the bottom of the optic. The acetone was repeated, for a total of 2 acetone wipes. Because acetone evaporates very quickly, more acetone is used than isopropyl. The optimal amount turned out to be ~115 microliters of acetone. It is hard to say exactly how much I had on the second wipe, because the syringe is not marked past 100 microliters. On the first wipe, with about 105 microliters, the lens paper was too dry at the bottom of the optic.
We then switched to Isopropyl. A new syringe was used, and again we rinsed it by filling it completely with isopropyl, and emptying it onto a kimwipe. This was repeated at least twice. We followed the same procedure for applying liquid to the optic and wiping the optic with the lens paper. On the first try with isopropyl, we used 100 microliters, since that was the preferred amount for acetone. Since isopropyl evaporates much slower than acetone, this was determined to be too much liquid. On the second isopropyl wipe, I filled the syringe to 50 microliters, which was just about perfect. The isopropyl wiping was done a total of 2 times.
After wiping, we replaced the front bottom earthquake stop, and released the optic from the other earthquake stops' clamping. The OSEM values were checked against the values from the screenshots taken yesterday afternoon, and were found to be consistent. Koji took more photos, all of which will be placed on the 40m Picasa page.
We visually inspected the optic, and we couldn't see anything on the optical surface of the mirror. Koji said that he saw a few particulates on some horizontal surfaces in the chamber. Since the optic seemed (at least to the level of human vision without a strong, focused light) to be free of particulates on the optical surface to start with, the suspense will have to remain until we button down, pump down, and try to lock the IFO to determine our new finesse, to see if the wiping helped any substantial amount.
We replaced the regular, heavy door on the inner side of the ETMX chamber (the side closer to the CES building), and put only a light door on the outer side of the chamber (the side closer to the regular walkway down the arm). We will look at the spectra of the OSEMS tomorrow, to confirm that none of the magnets are stuck.
We commence at ~9am tomorrow with ETMY.
* The LED lights are awesome. It's easy to use several lights to get lots of brightness (more than we've had in the past), and the chamber doesn't get hot.
* We should get larger syringes for the acetone for the large optics. It's challenging to smoothly operate the plunger of the syringe while it's so far out. We should get 200 microliter syringes, so that for the acetone we only fill them about half way. It was noticeably easier to apply the isopropyl when the syringe only had 50 microliters.
* It may be helpful to have a strong, focused optical light to inspect the surface of the mirror. Rana says that Garilynn might have such an optical fiber light that we could borrow.
Steve, Jenne, Koji
09:30 25 torr
10:30 180 torr
11:00 230 torr
12:00 380 torr
13:00 520 torr
14:30 680 torr - Finish. It is already over pressured.
There's a large broadband increase in the MC_F spectrum. I'm not totally sure it's real--it could be some weird bit-swapping thing. I've tried soft reboots of c1susvme2 and c1iovme, which haven't helped. In any case, it seems like this is preventing any locking success today. Last night it was fine.
Rebooting c1iovme (by keying off the crate, waiting 30 seconds, and then keying it back on and restarting) has resolved this. The frequency noise is back to the 'usual' trace.
NOTE: HEPA is on at its full.
[[[OK]]] Align the suspended optics (by Rob)
[[[OK]]] Align the oplevs again
[[[OK]]] Take snapshots for the suspensions/QPDs/IO QPDs/PZT strain gauges
[[[OK]]] Align the IP_POS, IP_ANG
[[[OK]]] Align the PSL table QPDs, the MC WFS QPDs, and the MCT QPD
[[[OK]]] Align the aux laser for the absolute length
Align the suspended optics (by Rob)
Align the oplevs again
Take snapshots for the suspensions/QPDs/IO QPDs/PZT strain gauges
Align the IP_POS, IP_ANG
Align the PSL table QPDs, the MC WFS QPDs, and the MCT QPD
Align the PSL table QPDs, the MC WFS QPDs, and the MCT QPD
Align the aux laser for the absolute length
o Go to only ITMX mode:
Save the alignment of the mirrors. Activate X-arm mode. Misalign ITMY and ETMX.
o Inject the aux beam:
Open the shutter of the aux NPRO. Turn the injection flipper on.
o Look at the faraday output:
There are several spots but only one was the right one. Confirm the alignment to the thorlabs PD. Connect the oscilloscope to the PD out with a 50Ohm termination.
Thanks to the Alberto's adjustment, the beat was already there at around 10MHz. After the PD adjustment, the DC was about 600mV, the beat amplitude was about 50mVpp.
o Adjust the aux beam alignment:
Adjust the alignment of the aux beam by the steering mirrors before the farady isolator. These only change the alignment of the aux beam independently from the IFO beam.
After the alignment, the beat amplitude of 100mVpp was obtained.
Close the shutter of the NPRO. Turn off the flipper mirror. Restore the full alignment of the IFO.
Taking a cue from entry 2346, I immediately went for the nuclear option and powered off fb40m. Someone will probably need to restart the backup script.
Backup script restarted.
We restarted daqd and it did restored the problem
Then restart the 'daqd' process:'telnet fb40m 8087', type "shutdown" at the prompt. The framebuilder will restart itself in ~20s.
telnet fb40m 8087
It did not related to the problem, but we also cleaned the processes related to dtt, dataviewer by pkill
After that the alignment scripts started to work again. As a result, we got some misalignment of the oplevs.
I am going to come on Sunday
- Align the optics
- Align the oplevs again
- Take snapshots for the suspensions
- Align the IP_POS, IP_ANG
- Align the aux laser for the absolute length
- Align PSL table QPDs, and MCT QPD
We aligned the full IFO, and centered all of the oplevs and the IP_POS and IP_ANG QPDs. During alignment of the oplevs, the oplev servos were disabled.
Koji updated all of the screenshots of 10 suspension screens. I took a screenshot (attached) of the oplev screen and the QPD screen, since they don't have snapshot buttons.
We ran into some trouble while aligning the IFO. We tried running the regular alignment scripts from the IFO_CONFIGURE screen, but the scripts kept failing, and reporting "Data Receiving Error". We ended up aligning everything by hand, and then did some investigating of the c1lsc problem. With our hand alignment we got TRX to a little above 1, and TRY to almost .9 . SPOB got to ~1200 in PRM mode, and REFL166Q got high while in DRM (I don't remember the number). We also saw a momentary lock of the full initerferometer: On the camera view we saw that Yarm locked by itself momentarily, and at that same time TRX was above 0.5 - so both arms were locked simultaneously. We accepted this alignment as "good", and aligned all of the oplevs and QPDs.
It seems that C1LSC's front end code runs fine, and that it sees the RFM network, and the RFM sees it, but when we start running the front end code, the ethernet connection goes away. That is, we can ping or ssh c1lsc, but once the front end code starts, those functions no longer work. During these investigations, We once pushed the physical reset button on c1lsc, and once keyed the whole crate. We also did a couple rounds of hitting the reset button on the DAQ_RFMnetwork screen.
A "Data Receiving Error" usually indicates a problem with the framebuilder/testpoint manager, rather than the front-end in question. I'd bet there's a DTT somewhere that's gone rogue.
The Ranger was left in a place where it could be bumped during next week's activities (near the crawl-space to access the inside of the "L" of the IFO on the Yarm). It has been moved a meter or so to a safer place.
Also, so that Steve can replace the battery in the SR560 that is used for the Ranger, I swapped it out with one of the ones which already has a new, charged battery. All of the settings are identical. For posterity, I took a pic of the front panel before unplugging the old SR560.
Today I measured the max output power at the EOM output of one of the RF AM Stabilizers that we use to control the modulation depth. I needed to know that number for the designing of the new RF system.
When the EPICS slider of the 166 MHz modulation depth is at 0 the modulation depth is max (the slider's values are reversed : 0 is max, 5 is min; it is also 0 for any value above 5, sepite it range from 0 to 10).
I measured 9.5V from the EOM output, that is 32 dBm on a 50 Ohm impedance.
Came back from dinner to find the Mach Zehnder unlocked. The poor IFO is kind of having a crappy day (computers, MZ, and I think the Mode Cleaner alignment might be bad too).
I found the FEsync light on the OMC GDS screen red. I power cycled C1OMC, and restarted the front end code and the tpman. I assume this is a remnant of the bootfest of the morning/weekend, and the omc just got forgotten earlier today.
When Alberto was parting the Red Sea this morning, and turning it green, he noticed that the wireless had gone sketchy.
When I checked it out, the ethernet light was definitely blinking, indicating that it was getting signal. So this was not the usual case of bad cable/connector which is a known problem for our wireless (one of these days we should probably relay that ethernet cable....but not today). After power cycling and replugging the ethernet cable, the light for the 2.4GHz wireless was blinking, but the 5GHz wasn't. Since the wireless still wasn't working, I checked the advanced configuration settings, as described by Yoichi's wiki page: 40m Network Page
The settings had the 5GHz disabled, while Yoichi's screenshots of his settings showed it enabled. Immediately after enabling the 5GHz, I was able to use the laptop at Alberto's length measurement setup to get online. I don't know how the 5GHz got disabled, unless that happened during the power cycle (which I doubt, since no other settings were lost), but it's all better now.
Came in, found all front-ends down.
Keyed a bunch of crates, no luck:
Requesting coeff update at 0x40f220 w/size of 0x1e44
No response from EPICS
Powered off/restarted c1dcuepics. Still no luck.
Powered off megatron. Success! Ok, maybe it wasn't megatron. I also did c1susvme1 and c1susvme2 at this time.
BURT restored to Nov 26, 8:00am
But everything is still red on the C0_DAQ_RFMNETWORK.adl screen, even though the front-ends are running and synced with the LSC. I think this means the framebuilder or the DAQ controller is the one in trouble--I keyed the crates with DAQCTRL and DAQAWG a couple of times, with no luck, so it's probably fb40m. I'm leaving it this way--we can deal with it tomorrow.
I found the red sea when I came in this morning.
I tried several things.
I'm now going to restart the single front -ends and burtgooey them if necessary.
Everything is back on.
Restarted all the front ends. As usual c1susvme2 was stubborn but eventually it came up.
I burt-restored all the front-ends to Nov 26 at 8am.
The mode cleaner is locked.
I stopped by the 40m for some reason and found that the MC trans was 7.5.
This was caused by an oscillation of FSS, which seemed to be started by itself.
The oscillation stopped by reducing the FSS total gain to +9dB (from +11dB).
This is not a permanent fix (i.e. autolocker will restore the gain).
If it seems necessary to reduce the FSS gain always, we change the MC autolocker script.
I measured the open loop gain of the PLL in the AbsL experiment.
Plots don't really make sense. The second one is inherently unstable - and what's g?
The key point of the story is:
"The recipe to exploit maximum benefit from a resonant EOM"
- Make a resonant EOM circuit. Measure the impedance Z at the resonance.
- This Z determines the optimum turn ratio n of the step-up transformer.
(n2 = Z/Rin where Rin is 50Ohm in our case.)
- This n gives the maximum gain Gmax (= n/2) that can be obtained with the step up transformer.
And, the impedance matching is also satisfied in this condition.
OK: The larger Z, the better. The higher Q, the Z larger, thus the better.
(Although the relationship between Z and Q were not described in the original post.)
So, how can we make the Q higher? What is the recipe for the resonant circuit?
=> Choose the components with smaller loss (resistance). The details will be provided by Kiwamu soon???
When I was young (3 months ago), I thought...
I was just too thoughtless. In reality, they are closely related each other.
A high Q resonant circuit has a high residual resistance at the resonant frequency. As far as the impedance is higher than the equivalent output impedance of the driving circuit (i.e. Z>Rin n2), we get the benefit of increasing the turn ratio of the transformer. In other words, "the performance of the resonant EOM is limited by the turn ratio of the transformer." (give us more turns!)
OK. So can we increase the turn ratio infinitely? No. Once Rin n2 gets larger than Z, you no longer get the benefit of the impedance transforming. The output impedance of the signal source yields too much voltage drop.
There is an optimum point for n. That is the above recipe.
So, a low Q resonant EOM has a destiny to be useless. But high Q EOM still needs to be optimized. As far as we use a transformer with a low turn ratio, it only shows ordinary performance.
Now I am studying about the behavior of the Q-factor in the resonant circuit because the Q-factor of the circuit directly determine the performance as the EOM driver.
Here I summarize the fundamental which explains why Q-factor is important.
The EOM driver circuit can be approximately described as shown in figure below
Z represents the impedance of a resonant circuit.
In an ideal case, the transformer just raise the voltage level n-times larger. Rin is the output impedance of the signal source and usually has 50[Ohm].
The transformer also makes the impedance Z 1/n^2 smaller. Therefore this configuration gives a following relation between Vin and Vout.
Where G is the gain for the voltage. And G goes to a maximum value when Rin=Z/n2. This relation is shown clearly in the following plot.
Note that I put Rin=50 [Ohm] for calculating the plot.
Under the condition Rin=Z/n2( generally referred as impedance matching ), the maximum gain can be expressed as;
It means that larger Z makes more efficient gain. In our case, interested Z is considered as the impedance at a resonance.
I closed the shutter of the NPRO for the night.
I repeated the measurement twice: one with gain knob on the universal PDH box g=3.0; the second measurement with g=6.0
The UGF were 60 KHz and 100 KHz, respectively.
That means that one turn of the knob equals to about +10 dB.
Last night something happened on the beat between the PSL beam and the auxiliary NPRO beam, that spoiled the quality of the beating I had before. As a result the PLL has become unable to lock the two lasers.
The amplitude of the beat at the spectrum analyzer has gone down to -40 dBm from -10 that it was earlier. The frequency has also become more unstable so that now it can be seen writhing within tens of KHz.
Meanwhile the power of the single beams at the PLL photodiode hasn't changed, suggesting that the alignment of the two beam didn't change much.
Changes in the efficiency of the beating between the two beams are not unusual. Although that typically affects only the amplitude of the beat and wouldn't explain why also its frequency has become unstable. Tuning the alignment of the PLL optics usually brings the amplitude back, but it was uneffective today.
It looks like something changed in either one of the two beams. In particular the frequency of one of the two lasers has become less stable.
Another strange thing that I've been observing is that the amplitude of the beat goes down (several dBm) as the beat frequency is pushed below 50 MHz. Under 10 MHz it even gets to about -60 dBm.
I noticed the change yesterday evening at about 6pm, while I was taking measurements of the PLL open loop tranfer function and everything was fine. I don't know whether it is just a coincidence or it is somehow related to this, but Jenne and Sanjit had then just rebooted the frame builder.
Problem found. Inspecting with Koji we found that there was a broken SMA-to-BNC connector in the BNC cable from the photodiode.
I checked C1:PSL-FSS_VCODETPWR. The attached is the 4 months trend of the FSS RCTRANS / RFPDDC(=FSS REFL) / VCODETPWR / VCOMODLEVEL.
Although VCO modulation level setting was mostly constnt, VCODETPWR, which presumably represents the RF level, changes time by time.
It coincides with the recent reduction of the RCTRANS/RFPDDC. Actually, my touch restored the VCO to the previous more stable state.
One can see that this is not only a single occation, but it happened before too. (In the middle of Aug.)
This could be explained by the bad contact of some cable or connector.
Nevertheless we need more careful investigation:
1. Understand what VCODETPWR is exactly.
2. Investigate relationship between VCOMODLEVEL / VCODETPWR / AOM deflection efficiency / RCTRANSPD
3. Confirm the frequency matching between the VCO and AOM.
but the increase in both the RCtrans and the RCrefl is consistent with my theory that the power going to the RC has increased ; its not just an increase in the visibility.
We should scan the AOM/VCO to make sure the frequency is matched to the resonance to within 0.5 dB.
I'm working on the AP table. I also opened the auxiliary NPRO shutter. The auxiliary beam is on its path on the AP table and PSL table.
NPRO shutter closed
What I meant was the VCO driver, not the FSS box.
As for the frequency, all written numbers were the Marconi displays.
The number on the frequency counter was also recorded, and so will be added to the previous entry shortly...
I propose that from now on, we indicate in the elog what frequencies we're referring to. In this case, I guess its the front panel readback and not the frequency counter -- what is the frequency counter readback? And is everything still locked to the 10 MHz from the GPS locked Rubidium clock?
Plus, what FSS Box? The TTFSS servo box? Or the VCO driver? As far as I know, the RC trans PD doesn't go through the FSS boxes, and so its a real change. I guess that a bad contact in the FSS could have made a huge locking offset.
Locking has gone sour. The CARM to MCL handoff, which is fairly early in the full procedure and usally robust, is failing reliably.
As soon as the SUS-MC2_MCL gain is reduced, lock is broken. There appears to be an instability around 10Hz. Not sure if it's related.
Whatever the locking problem was, the power of magical thinking has forced it to retreat for now. The IFO is currently locked, having completed the full up script. One more thing for which to be thankful.