Stefan, Evan

Summary

Adding an offset to the error point of the ASB36I→SRM yaw loop reduces the SRCL→DARM coupling by 10 dB. It seemingly has the added benefit of fixing the slow drift in POP90.

Details

SRM yaw loop offsets

After several days of trying to do SRCL feedforward on a moving target, we decided to try attacking the SRCL→DARM coupling itself.

We started by applying offsets to the dETM loops, since Gabriele's simulation seemed to indicate that this could cause an increase in the high-frequency coupling. We applied offsets of several hundred counts (both signs) to dETM pitch and yaw, and then injected broadband noise in SRCL. We saw a reshaping of the noise (see attachments), but no overall improvement.

Then we moved on to offsets in the SRM WFS yaw loop. Here we saw a more promising improvement with a positive offset at the error point (see attachment). In the end we found that an offset of 2100 ct works best in terms of reducing the coupling at high frequencies. This also seems to coincide with minimal power in POP90.

POP90 stabilization

With this yaw offset engaged, it seems that the drift in POP90 mostly went away when the SRM yaw offset was engaged around 09:14:00 (attachment). There is still some drifting, but the timescale is much longer. Perhaps we are closer to optimal coupling of the 45 MHz sidebands into the SRC. This particular lock lasted for about 2.5 hours (it broke for unrelated reasons) and showed no sign of the POP90/ASB36I instability that we've seen this past week.

DARM offset and calibration

For some additional reduction in SRCL coupling, we tried locking with a smaller DARM offset (14 pm, not 7 pm as I said before) and then updated the calibration (FM10 in the sensing inversion of CAL-CS). However, I have reverted these changes. This means that in general you should not believe the recorded inspiral range for most of the night.

Guardian changes, other configuration changes

If LSC_FF is requested, the Guardian will proceed from DC_READOUT to LOWNOISE_ESD_ETMY to LSC_FF. If desired, one can make a pit stop at COIL_DRIVERS before going through LSC_FF.

I had wanted to add some Guardian code that steps down the TRX/TRY QPD whitening gains by 6 dB before the ASC comes on (and then adjusts digital gains accordingly), since the QPDs will saturate when powering up beyond 10 W. But it seems this makes the ITM loops unstable somehow. So I've left some commented-out code in DRMI_ON_POP and in the DOWN state.

In the ITM M0 lock filters, I moved the integrators from FM2 to FM4 and stuck +20 dB gains in FM2. Now we have some room to adjust the offloading speed.

The move of the piezo mirror from the top of the periscope to the table top (Link) left large features in DARM at least in part because a resonance of the mirror mount that replaced the piezo mirror mount, overlapped with a higher frequency periscope peak, just as the lower frequency resonance of the piezo mounting had overlapped with a periscope peak at lower frequencies. Figure 1 shows, in red, periscope spectra before tuning, and, in blue, after tuning. The idea was to move the optic resonances, indicated by the high DARM coherence in red at 340 and 390 Hz, into the red valley centered at about 310 Hz by adding weight.  The blue trace shows that the peaks were moved to 310 and 340 and the coherence with DARM was reduced.

Figure 2 is an “after” photo showing the weight that was clamped to the mirror mount to make this change. In addition, figure 2 shows the safety cover, which covers the vertical path of the beam, that is responsible for the peak just below 300 Hz. Unlike the rest of the periscope, this safety cover is not damped and definitely needs to be - the safety cover resonance is showing up in DARM.

I also added a little weight to the top of the periscope to reduce coherence with DARM at 190 Hz by splitting overlapping resonances. This also helped.

I think that the next step is to minimize jitter coupling from the PSL table to DARM, possibly by injecting a peak using the PSL piezo and modifying alignment to minimize the height of this peak in the IM4 pitch and yaw signals and eventually by minimizing the injected peak height in DARM. 

This morning ALS/green arm alignment was touched up.  But Y-arm kept dropping out of lock eventhough it had powers around 1 (think this might have been issue of Guardian fighting us &misaligned ITMs.  The ISS Ref Signal was also moved from -2.02 to -1.98).  After this we had issues with the PRC (Keita pointed out saturations on PRM, and so we (1) "Cleared History" for the M1 LOCK P&Y paths & (2) restored the Pit & Yaw biases to where they were earlier in the morning.   Then we plugged through & locked up the ifo.

• 8:48am:  Jeff/Peter rolling chiller from Receiving thru LVEA to Mechanical Room
• 9:59am:  Jodi/PeterK at MY
• 1:30-1:40pm:  Kyle walked the LVEA for any possible roof leaks:  None found
• Ifo handed over to Commissioners in the afternoon

We repeatedly had problems with engaging ASC loops to the bottom or penultimate mass that have a top stage relieve loop.

In a nutshell, the problem comes with engaging the loop with a relatively big initial misalignment. The fast loop to PUM or TST does the right thing, but saturates its drive stage before the top mass relieve can kick in. Increasing the top mass relief doesn't always work because different loops feed the same test mass.

The ideal approach would be a saturable integrator in the ASC filter banks. Since this this would require a front-end code change, I wrote a python version that watches filter module output and input, and simply turns the input off if the integrator exceeded the limit and the error signal would drive it further away.

The code relies on guardian decorators. I.e. it should be added to any state during which this logic should be active. The decorator is defined in ISC_library.py, and can be called as:

    @FM_limit_checker_decorator(ListOfFIlterModulePrefixes_pos_gain,+1)
    @FM_limit_checker_decorator(ListOfFIlterModulePrefixes_neg_gain,-1)

Example:
    @FM_limit_checker_decorator({'ASC-SRC2_P','ASC-SRC2_Y','ASC-DSOFT_Y','ASC-CSOFT_Y'},+1)
    @FM_limit_checker_decorator({'ASC-DSOFT_P','ASC-CSOFT_P'},-1)

Positive and negative gain characterizes the overall gain of all engaged filters, i.e.
 - +1 : positive input signal leads to growing output signal and vice versa
 - -1 : positive input signal leads to shrinking  output signal and vice versa



Current testing:
================
 - For initial testing we added the decorator to

i) DRMI guardian ENGAGE_DRMI_RUN state:
    @FM_limit_checker_decorator({'ASC-SRC2_P','ASC-SRC2_Y'},+1)

ii) ISC guardian ENGAGE_ASC run state:
    @FM_limit_checker_decorator({'ASC-SRC2_P','ASC-SRC2_Y','ASC-DSOFT_Y','ASC-CSOFT_Y'},+1)
    @FM_limit_checker_decorator({'ASC-DSOFT_P','ASC-CSOFT_P'},-1)

Known bugs:
===========
 - Currently the filter module will be left in whatever state it was when the decorator ran for the last time. It is up to the user to assure the filter module is actually on in the end.


The full code in ISC_library.py is:
---------------------------------------------------------------------------------------------------
def FM_limit_checker_decorator(FMlist,sign):
    class FM_limit_checker(GuardStateDecorator):
        """Check for FM reaching limiters - if so, turn of input"""
        def pre_exec(self):
            for FM in FMlist:
                if  ((-ezca[FM+'_OUTMON'] >= ezca[FM+'_LIMIT']) and (-ezca[FM+'_INMON']*sign> 0)) or
                    (( ezca[FM+'_OUTMON'] >= ezca[FM+'_LIMIT']) and ( ezca[FM+'_INMON']*sign> 0)) :
                    ezca.switch(FM, 'INPUT', 'OFF') 
                else:
                    ezca.switch(FM, 'INPUT', 'ON')   
    return FM_limit_checker

Reports from Subsystems:

• SEI:  Timing distribution work went well.  Feedforward filter development for HAMs continues.  HAM2 STS2 continues to show problems.
• SUS:  Nothing to report
• PSL:  FSS back to a better #.  Issue of trips still unresolved 
• Commissioning:  AI swap next week, SRCL Feedforward & WFS work today
• Facilities/VAC:  leak in kitchen, and painting should be complete by Thurs

Scott L. Ed P. Chris S. (Cris M.1/2 day)

5/11/15
45.7 meters cleaned ending at HNW-4-040. Test results posted here. Removed lights, refilled D.I. water tank and relocated all equipment to next section north.

5/12/15
The crew began hanging lights,vacuuming support tubes and spraying bleach/water solution. Cleaned 54.9 meters ending 11.5 meters north of HNW-4-042.

5/13/15
Cleaned 67 meters ending at HNW-4-046.

To date, we have cleaned a total of 2902 meters of tube.

The original PSL chiller has been fitted out with the vortex style flow sensor.  In
turning the crystal chiller on, we found that the controller unit was faulty and did
not display the Termotek logo on start up.  The controller was replaced and the chiller
powered up okay.  We ran the chiller with the outlet connected to the inlet without any
problems.  The flow sensor calibration factor was changed to 0970 to account for the
vortex sensor.

The exercise was repeated with the diode chiller.

At the moment the chillers are in the large item access area, waiting for a convenient
time for us to roll them back to the chiller room.  The crystal chiller needs another
pigtail cable to be made.



JeffB, Peter

No real changes from the report yesterday afternoon.  That data was from the afternoon after things quieted down in the LVEA.  Data from this morning ~0030pdt, look pretty much the same.   There are bands of elevated signal compared to the references: ITMX & BS ST2 Verticals below 20Hz.  The BS Stage2 Corner2 signals are lower now by factors or 2 & 3 above 20 Hz (good thing.)  The ITMX sees increased noise above 20Hz on V1 both stages and on ST2 H2 above 10Hz.  In general, ITMY looks little changed and pretty good.

Happy if RichM or another well studied would look at these too.

10 day trend.

Noticed it on the way out...

Evan, Stefan

We fine-tuned the MICH correction todonight.
- Added the SB300vio BS violin stop band filter to MICH_FF to cancel their effect.
- Measured MICHFF_OUT to DARM_IN twice:
    1) drive disconnected at the ITMY. This measures the MICH_OUT to DARM_IN path.
    2) MICH_FF input off, driving MICH_FF. This measures the MICHFF_OUT to DARM_IN path. 
  This data is in plot 1.

- 1)/2) is the desired filter, shown in  plot 2.

- Finally, we used a p:60:z:80 filter to fine-tune the phase a bit. (Plot 3) This significantly improved the achievable subtraction.

Evan, Stefan,

Our late night work was hampered by repeated lock-losses engaging SRC2 loop during the DRMI phase. The few times we made it through that stafe, we lost it in the IFO ASC stage, when the SRCL2 loop gets extra gain.

We tried both a high SRCL offload and low SRCL offload configurations (Gain of 1 and 0.1 respectively in SRM M2 stage.) The high SRCL offload configuration resulted in a 18sec oscillation, growing to a lock-loss.  The low configuration (the default) also broke the loss several times, but we are not sure why.

Sheila, Evan, Stefan

We remeasured the required SRCL FF filter today. The transfer function changed significantly.
The only thing we know we changed was the POP_45 phase (H1:LSC-POP_A_RF45_PHASE_R) from 66deg to 58deg - this minimized a SRCL drive in MICH.

The fit functions are roughly:

May 11: p:0,0  z:2.28571+31.9183i,2.28571-31.9183i,-180    (M1)
May 12: p:0,0  z:2.28571+47i,2.28571-47i,-600              (M2)

The 1st attached plot shows these two measurements, overplayed with the models M1 and M2.
The 2nd plot shows the 4 raw measurements (2 yesterday, 2 today).

We didn't try to engage this SRCL FF yet.

SudarshanK, DarkhanT

We introduced two Pcal lines at 240 Hz and 310 Hz on photon calibrator at Y end.  The Pcal lines are about a factor of 10 above the DARM sensitivity at those frequencies. We will look into any changes in the amplitude and phase of these lines to determine the the position of cavity pole frequency. The cavity-pole has been observed at frequencies listed in  alog LHO #18360.