I tried out a different version of the charge measurement. I'll detail it more later but the gist of it is that I drive the pitch of the TM using the built-in frontend lockin and feed back the lockin output to an offset on the ESD quadrant drive. This is done without any DC bias on the full face bias electrode.

In any case the effective offset voltage I measure for the four ESD quadrants are:

LR: 184V

LL: 159V

UR: 1V

UL: 12V

To understand the origin of the offsets I had to add ot almost all IMC ASC loops, I recentered the two IMC WFS, using the picomotors.

The offsets changed, but they didn't go to zero. So we can now conclude that the offsets are dependent on the WFS centering, as expected.

Then, I started moving around the beam on MC2_TRANS QPD, again using the picomotors. This alos had an effect on the intensity noise coupling. I removed all offsets from the loops, moved the beam on MC2_TRANS, trying to minimize intensity noise. This task was particularly difficult, for two main reasons. First, every time I moved the beam on MC2_TRANS, I had to recenter the beam on WFS_A and WFS_B. Second, HAM3 ISI tripped few times, messing up with my tests.

However, I believe I found a good position of the beams on the QPDs/WFSs. At present, there are no offsets in the loops, and the beam spot position on MC2_TRANS should be good enough to give us low intensity noise.

I checked the optimal offsets using the usual scatter plots, and it appears that things could still be improved with an offset in DOF_1_YAW, so the present position is not yet optimal. More tweaking tomorrow, but only in the case the present offsets remain stationary over night.

I also recenter IM4_TRANS_QPD.

Hugh, Evan, Kiwamu,

Since Keita established a new good SR3 alignment (alog 15020), we tried moving the oplev QPD to center the beam on it. However it turned out that the beam seems to be largely clipped on its way to hit the QPD. We could not identify what clips the beam.

We decided to steer SR3 back to the old angle such that we can reliably engage the oplev damping loop for tonight. This should be fixed tomorrow morning.

(some details)

When SR3 was on the new alignment values, the sum of the oplev signals was about 200 counts. We thought this was due to the beam mostly falling off from the QPD, but it turned out that the beam was actually still on the QPD but with the most of it clipped somewhere. We also made sure that we did not catch a ghost or some kind of fake beams by moving the QPD stage around. We steered SR3 back to the old angle and saw the sum going back to 30000 counts or so with pitch and yaw going back to 30 urad or so from 0 urad in the oplev screen. We are concluding that the oplev beam is clipped at some point between the SR3 optic and the QPD when SR3 is in the new angle. We need to open the receiver box and see what is going on. For tonight, we decided to set SR3 back to the old angle in order for us to be able to engage the oplev damping loop which was a key for stable SRC.

Bubba and I are making progress understanding the control logic (and illogic?) of our VEA control loops. We have turned on heaters in all three VEA/LVEA areas in order to compensate for the cold front.

Provided we have made sensible changes to the system we should see things stabilizing overnight.

One mechanical problem found was an outside air damper at Y END which was not able to close - therefore admitting a significant amount of cold outside air. We did not have a similar problem at X END where the excursion was much less pronounced.

Hopefully this mechanical fix and some parameter changes will settle things.

Dan, Fil

We've modified the QPD transimpedance board for the ASC-AS_C QPD so that the SUM output that's used for the fast shutter triggering no longer saturates when the DRMI is locked at 10W.  We swapped R23 from a 20k ohm resistor to 1.24k ohm; this change reduces the amplification of the SUM output by 16x and brings the board (S1301506) into agreement with version 6 of the schematic (D1001974).  [NB: with the DRMI locked at 10W we observed ~3.3mW on ASC-AS_C, or ~130mW into HAM6; this is dominated by the 45MHz sidebands and it roughly aligns with what's expected at 10W (65% transmission of 45MHz sidebands to the AS port, Gamma2=0.28 gives 112mW into HAM6 -- probably we are getting some extra light from higher order modes).] 

We also modified the controller box for the HAM6 shutters to have the correct output polarity.  The output from the box (S1203609) was previously +5V on a trigger condition (shutter CLOSED) and 0V on a nominal condition (shutter OPEN).  We implemented the version 2 modifications to the board (D1102312), namely connecting pin1 of U8A (the OUTN signal) to the front-panel OUT connector, and connected P2 pin1 (the OUT signal, opposite polarity from OUTN) to the J1 pin10 slot on the D880C card.  Note that we only modified channel1 in this box, we left channel2 as we found it.

Now, the SUM output from ASC-AS_C should not exceed 1V when the DRMI is locked (unless we mode hop?), and the controller output will be logic-low upon a trigger condition.  The trigger output has been connected to the OMC PZT driver board, we'll commission the PZT shutter function soon.  (Zach's results from L1 are here.)

I've verified that the trigger function works from the control room via the Beckhoff interface.  The code for this function may need to be modified to accomodate the toaster shutter, which has its own Beckhoff interface and will record a fault condition if the input from the shutter controller is logic-low for too long.  Currently the shutter controller will not reset the trigger logic without user intervention; it might be a good idea for the logic signal to reset itself after the PD input has passed below threshold, and have the fast shutter state remain closed (i.e., toast up) until a user/guardian/script opens it.

8:00ish Karen, Kris, Aaron in LVEA
9:00 JeffB, Andres to LVEA
9:15 Fil, Karen, Kris to EY
10:00 Betsy Travis to LVEA West Bay
10:45 Gerardo to H2 PSL enclosure
11:00 Fil to EY
13:30 Fil to CER
14:30 DanH to HAM6
15:00 Kiwamu to ISCT6
 

J. Kissel, A. Staley, K. Izumi, K. Kawabe

Continuing investigations of why ETMY behaves poorly when attempting ALS DIFF (see LHO aLOG 15037) -- I've looked at two more things:
(1) Pitch-only optical lever Damping: This had been turned on only *after* it had been decided that ETMY was "fragile," i.e. any impulses would shake the SUS quite a bit -- but I checked it anyways. First attachment is comparing spectra with the PUM (L2) stage actuated, optical lever Pitch damping loop ON vs. OFF. It's damping pitch, as expected, and not injecting anything terrible. This of course is assessing the stationary noise, and we're worried about non-stationary problems ... but ruling things OUT with quantitative data, I feel, is just as important along the investigatory route.

(2) DRIVEALIGN Matrices: I attach comparisons between everything in the ETMs UIM (L1) DRIVEALIGN matrices (Only the P2P, Y2Y, and L2P have anything in them, so those are what's compared in the attachment). I believe the original design intent for P2P and Y2Y filters was to have global WFS transfer function be similar to the test-mass transfer functions -- hence the high-Q, plant inversion-y type stuff. They are slightly different between the two test masses, but, in-fact, they don't matter matter at all because we don't feed any angular signals to the UIM stage. 

However, I've found that the ETMY UIM L2P frequency-dependent decoupling filter in the UIM bank is significantly different than ETMX's -- and the filter has a much larger step response. I compare three different sets of filters on pgs 1 and 2:
ETMX -- FM1 & FM2, "L2P" & "L2P2" 
ETMY, Current -- FM1, FM2, & FM4 "L2P", "L2P2", and "BetterRolloff"
ETM, Legacy -- FM6 & FM7,  "L2Plegacy" & "L2P2legacy" 
It looks like the initial story here is laid out in LHO aLOG 11832, but there're several more aLOGs referencing UIM / L1 L2P Filters, and how they've been bad, they've been good, they've been turned off, they've been turned on...

The foton calculation of the step response disagrees with the measured step response LHO aLOG 14832 -- but recall that the filter step response is not the only thing measured in that 14832 measurement -- it's measuring both the filter AND mechanical step response. We now have local damping filters from LLO which has reduced the mechanical impulse response time by a factor of a few. This, coupled with a smaller impulse response filter should help, but we'll remeasure once a new filter is designed.

I'll move on to chasing this down -- re-measure the step response, and also remeasure the plant upon which these filters were designed.

Of course, an immediate, band-aid fix could be just to copy ETMX's L2P filter over to ETMY, but while we wait for the temperature in the VEAs to settle down, I've been given the green light to measure some TFs.