In the past two or three days, Sheila, Dan and I have worked more on switching of the ETM actuators from the ESD to L2 stage with the goal of reducing the ESD DAC noise (see Evan's latest noise budget). Last night, I was again able to reduce the ESD biases all the way to zero by actuating on the ETMY L1 and L2 stages (see previous attempts in alog 17267). The DARM spectrum improved in 30-200 Hz band as expected, but only by a factor of ~ 1.7. Lock was not so stable (which seemed to be related to a peak at 12.52 Hz) and it stayed locked only less than 10 minutes. I was not able to test different bias voltages yet.

(DARM noise)

Here are two DARM spectra, one with the 380 volts ETMX ESD bias (in purple) and the other with zero bias voltage (in red). The ETMY ESD had zero DAC voltage in all the quadrants and bias all the time. As you can see, the noise floor went down in 30-200 Hz band with a slight increase at around 20 Hz. Also a peak at 12.5 Hz has been prominent in this week (for example, look at alog 17355) and it looks like this peak rings up every time before we lose lock. The peak usually becomes clearly visible in the DHARD signals in time series several seconds before the lock loss.

(Actuation Scheme)

We used to switch off the ETMX ESD and switch on the ETMY L2 stage while keeping the ETMX L1 stage active (see alog 17267) in the last week. This time, we tried a different scheme in which we actuate the L1 and L2 stages of ETMY and we do not actuate ETMX at all. In a sense, this is a transition of the ETM suspensions from X to Y. Before trying the transition, we measured the transfer function of the L1 and L2 stages at different times in order to check the cross over frequency. The attached below is the ratio of the two transfer functions (i.e. L1 / L2) together with a LSC DARM open loop, L1 and L2 transfer function models:

As shown in the plot, the measurement can be mostly explained by the model. However, according to the model, the phase at 1.8 Hz touches 180 degrees and thus unstable at this frequency. Unfortunately our measurement incidicated that the ratio of L1/L2 exceeds unity gain at around 1.6 Hz and I noticed that this would be a potential risk of unstable loop. Indeed, this configuration gave me unstable DARM which rang up at 1.6-ish Hz as expected when I tried transitioning to ETMY. I decided to insert a lead filter around this frequency. With the lead filter (a simple zero-pole pair at 0.3 and 1.5 Hz respectively), the L1/L2 transfer function should now look like the following:

This has two cross-over points, one at 0.45 Hz and 1.8 Hz with phase mergines of 57 and 43 degrees. I installed the lead filter in FM8 of SUS-ETMY_L1_LOCK_L. This allowed a repeatable transition. The transition process is also coded in the ISC LOCK guardian.

Slowly, over the past week, I have found a set of filter settings that damp the violin modes.  In the tables below I identify the mode frequencies that are matched to each test mass; the matching was done based on which lines were suppressed or excited using bandpass filters in the L2_DAMP filter banks for each test mass.  I also indicate which filter damps that particular line. 

The filter settings are given at the bottom of each table.  For all the L2_DAMP filter modules, FM1 is the bandpass filter (with +120dB gain in the pass band), FM2 and 3 are phase shifters (+/-60deg respectively), and FM4 is a 100dB gain.  FM1 and FM4 are always on.  FM2 and FM3 are used as indicated.  The gain settings are included in the Guardian - the filters shouldn't change in the locking process, but I haven't updated the safe.snap files for the suspensions!

The attached figure compares the noise spectrum from Friday and today.  The first harmonics of the violin modes are now the dominant feature in the spectrum, along with 60Hz and the 2.5kHz BS butterfly mode.

Scott L. Ed P. Chris S.

Cleaned the remaining 12 meters of tube to X-1-6 double doors. Results are posted here.
Relocated lights and equipment this afternoon.
New generator arrived this afternoon. John & I removed from shipping crate, added engine oil, hooked the up the battery and test fired the engine. It is ready to go tomorrow morning.

Only ETMy and ITMy ISI SDFs have anything 'DIFF.'  These are the Blends Jim is running alogged 17295.   Attached is the DIFFs at ITMY; the numbers at endy are the same.  We'll likely save these as nominal soon.  Either the BURT or PRESENT settings will work if the SHTF.

Karen and Cris in LVEA
08:16 Hugh setting SEI guardian nodes to 'Ready', charging HEPI accumulator
08:22 Gerardo to LVEA to look at pump carts by HAM1 and HAM2
08:26 Hugh and Gerardo back
08:36 Corey to squeezer bay
09:04 Gerardo turning on power supplies for annulus ion pumps at HAM1 and HAM2
09:39 Jodi and Gary to LVEA near HAM6 to tag boxes
09:41 Gerardo done
09:45 Jim B. to mechanical room mezzanine
09:56 Jim B. back
09:56 Andres to LVEA to look for beam splitter part in west bay
10:15 Andres done
10:18 Jodi and Gary done
11:22 Pepsi truck through gate
11:33 Gerardo to HAM1 and HAM2
11:40 Gerardo done
12:57 Tour in CR
13:01 Jodi and Gary to west bay
13:03 Andres in LVEA
13:09 Corey to squeezer bay
13:23 Jodi and Gary done
14:34 Cheryl to VPW
16:17 Cheryl in optics lab

Plots are found in SeiSVN: HEPI/H1/Common/2015-03-18_H1HPI_PumpControllerNoise.xml

The reference traces are from Monday 17 March 0900utc before the Tuesday Maintenance Accumulator Charging.  The current traces are 24 hours later after the charging effort (BSC2SupplyNorth not done.)

My assessment is this assessment is a bit too noisy and this didn't make much difference.  All the controller improvements have made things pretty good already.  The largest coherence was in the BS RZ which shows some broadband signal between 10 and 100mhz and that is reduced a good bit.  However, there are spikes of greater coherences in other dofs.  I would never say this is not worth doing.  Jeff may have some suggestions to better assess this is worhwhile.

I added the plots now.

Summary: The twin bumps at around 3300Hz comes from the OMC LSC loop, which has a 100Hz UGF.

Of course OMC length dither at 3300Hz should make some sidebands in the DC readout by design, but these twin bumps look really unnecessarily big.

We can reduce these by making the OMC length bandwidth much smaller.

Details:

In the attached, Red is with nominal setting (H1:OMC-LSC_SERVO_GAIN=60 and H1:OMC-LSC_OSC_CLKGAIN=6).

Blue is with 50% servo gain but with nominal dither amplitude (SERVO_GAIN=30, CLKGAIN=6), so it has half the open loop transfer function of red.

Green is is with nominal servo gain and 50% dither (SERVO_GAIN=60, CLKGAIN=3), so again it has half the OLTF of red.

IF the OMC length signal is sensing the true OMC length as opposed to just some noise that is not proportional to the dither amplitude, the OMC length control signal (middle row) for green and blue should be the same. But in reality they're 6dB apart from 8Hz and up.

Also you will expect that the OMC length error signal (bottom row) for blue and green have the same shape but different by 6dB, as the OLTF is the same but the sensing is 6dB different. That's only the case for f<8Hz.

So it's all noise for f>8Hz, and probably that's just  the noise floor of DC readout at 3300+-f Hz downcoverted by the demodulator (not dither) to f Hz, fed back to the OMC length, and upconverted by the dither back to 3300+-f. See the left column. Blue and green on the top left are the same because the sideband amplitude around 3300Hz produced by this mechanism is proportional to the product of the feed back gain and the upconversion gain (dither), the sensing part is independent of the dither amplitude.

In summary,

• OMC length signal is dominated by some noise, probably DC readout noise floor, not length fluctuation, from 8Hz and up.
• We can reduce the BW of the length control to maybe a few Hz to make the bump smaller and see if there's any ill effect on the DC signal.
• We can also filter out the feedback to make the width of the bumps smaller.

Later Dan will try some low BW filters.

(John W, Gerardo M)

Turned on the ion pumps at 9:05 am local time with both pump carts valved in, both pump carts were on the low 10^-06 torr

At 11:40 am I valved out the pump carts, but left the pump carts ON (connected to the annulus system and running).

Yeah :)

Obtained an alternate head to the charging hose.  Took down corner SEIs (Guardians to ready), turned Pressure servo to 0 psi.  Charged accumulator to 70psi.  Returned pressure servo to nominal and brought SEI back on via guardian.  Couple platforms tripped while deisolating and a couple (HAM2 & HAM3) tripped a couple times on the way back up.  All nominal now.

CDS
Filiberto moving SEI teststand from staging building to H2 building

Facilities
Bubba working by metal recycling container
Bubba looking at possibility of moving crates at mid X
Beam tube washing continues
Gerardo working on vacuum pumps by HAM1 and HAM2

3IFO
Corey working in squeezer bay
Other work on floor TBD

Operations
Suresh is giving training on optical levers at 11 in the large conference room

There has been an intermittent issue with the OMC_LOCK Guardian in which it runs a portion of code twice.  I've observed this most often in the OMC_LSC_ON state, where the LSC controls for the OMC are ramped up.  It's easy to notice, because if the gain steps are repeated for the OMC length servo the loop quickly becomes unstable and the cavity unlocks.  I've noticed this happen a handful of times in the past few weeks.  I've also seen lines of code in other main() function get executed twice, although I don't have screenshots to prove it.

Attached are screenshots of the OMC_LOCK log, from an event last week (March 14), and another tonight.  In both screencaptures, the OMC guardian enters the OMC_LSC_ON state, completes the instructions in main()...and then starts all over again.  In both cases the requested state was well downstream of OMC_LSC_ON, the guardian should not have looped there.  (And anyways, how does it repeat the main() function?)

I've committed the latest version of the OMC_LOCK guardian to the SVN, if experts want to check the code to make sure I'm not doing something heinous in the function calls or definitions.

In other locking notes from tonight...

• Kiwamu and I investigated the source of BS/SRM saturations, and a few locklosses, in the analog CARM handoff.  These saturation events had been variously blamed on the DRMI_ON_POP transition or the ASC loops turning back on, all of which happen in a short window of time.  Tonight we discovered it's due to the analog CARM handoff, specifically when input 2 of the REFL CM servo board is enabled with a large (14dB) input gain.  (This is the input of REFLAIR9I from the summing board to the CM board.)  When the input is enabled there is a big kick to the DRMI optics, and the MICH ASC loops (still engaged in this state) experience a large transient that rings for several seconds due to the inverse BS plant filter.  Screenshot of a typical lockloss is attached.  We've smoothed out the transition by putting a 10-second sleep in after the REFL_SERVO_IN2EN step.  No more locklosses from analog CARM.
• Violin mode damping is nearly finished.  There's one very tricky mode on ETMX that is a very problematic phase.
• We've continued to use Kiwamu's gains from Monday night to damp the ETMY and ITMX roll modes using AS_A_RF45Q, although I inserted a -100dB gain stage for ETMY to make the value more human readable.  Gain for ETMY_M0_DARM_DAMP_R is +40, gain for ITMX_M0_DARM_DAMP_R is +20.  These settings have not been propagated to the Guardian yet, I'd like to see if they continue to be robust after we touch up the ITM alignment to increase the recycling gain.
• We've been locking at 10W with the new DHARD_P filter.  Seems legit.

Dan, Keita, Kiwamu, Sheila

During a long, patient lock this evening I was able to measure the DHARD pitch loop down to 0.2Hz.  This follows Keita and Sheila's filter modifications to get some additional phase around the 3Hz UGF.  The attached plot is a record of the measurement (look at the RED trace), I have saved the xml file with the filename at the top of the plot.

The phase margin at the UGF is good (~40deg), and the loop does not cross unity gain at higher frequency.  There is almost a unity gain crossing at lower frequency, we have about 3dB of gain margin at 0.9Hz. 

Jamie, Dave, Jim:

Jamie reported that the location of the MEDM Print selection, being at the top of the right-mouse pull-down menu, has resulted in many accidental printer jobs. This explains the printouts of things like the sitemap screen with no data content and no one picking the print-outs up.

Jim modified the LHO CDS MEDM this afternoon to move the print section from the top to second from the bottom of the pull down menu. Please see the attached before and after images.

During tomorrow's maintenance we will stop all old MEDMs in the control room so the new feature will be picked up. This is only a linux change, it was not applied to Mac OS.