In preparation for tomorrow's maintenance on HAM2 and HAM3, I have set the following gains and whitening stages on HAM2 and HAM3 OPLEVs.

I added the dewhitening filters in the input flter banks of the oplevs and switched on two stages to mirror the analog state.   The analog switch states are shown in the attached pics. The label on the cable tells us the name of the oplev that is addressed by the dip-switch board. 

The oplevs are, as yet, not calibrated.  The HAM3 shows an uncompensated whitening though I have switched on the dewhitening filters stages.   Will investigate further.

There's a huge 364Hz line in ALS TRY.

I'm not sure if this was already there for a while. Though we probably changed the loop gain of the ALSY PDH loop when we realigned the green path on ISCTEX today.

J. Kissel

Continuing to compare L1 vs. H1 damping loop designs (see ), I've made a comparison of the QUAD's design, and also with the original low-noise design from which they're derived (see LHO aLOG 6760). Attached are the H1 and L1 designs compared against each other, 
dampingfilters_comparison_2014-11-07_LHOvs2014-11-10_LLO.pdf, as well as both against the original low-noise design dampingfilters_comparison_2014-11-07_LHOvs2013-06-14vs2014-11-10_LLO.pdf. 
As Sheila's quick comparison pointed out (see LHO aLOG 14923), the differences aren't that large (and detailed below).

In summary, both LHO and LLO have modified the low-noise design, but only slightly -- both apparently in order to get a reduction in test-mass impulse response. LLO took the "more sophisticated" in longitudinal by adding a boost instead of just increasing the overall gain, hence their modification preserves some phase margin. 

Because we're giving the LLO ALS DIFF control loops a try, however, we have copied over and installed the LLO design -- assuming that any little bit of difference will matter for these complicated global control transfer functions. Stay tuned...

- T, V, R loops are identical to the original design
The differences are the following modicifations:
- In L
     - LLO "resg1" boost ( resgain(f=1.07 [Hz], Q=4, height=13 [dB]) * gain(6, "dB") )
     - LHO overall gain increased by 2 (from -1 to -2).
- In P
     - LLO "notch60" 60 [Hz] notch ( notch(f=60 [Hz], Q=50, depth=40 [dB]) )
     - LHO overall gain increased by 3 (from -1 to -3).
- In Y
     - LLO "+12db" gain of 3.9811 ( gain(12, "dB") )

Comments:
In L, 
 - The extra "resg1" at LLO, significantly reduces the Q of the *second* (~1 [Hz]) L mode, and therefore significantly modifies the L to L and L to P global control transfer functions -- not only the resonant feature at 1 [Hz], but also the zero at 0.75 [Hz]. Other features are moved around a little, but no such significant change in shape. 
 - As such, the displacement from residual ground motion at 1 [Hz] has been reduced by a factor of 3, though (at least from the modeled input seismic motion) it doesn't contribute much to the over all RMS.  
 - The impulse responses of the two designs are comparable.

In V, and R,
 - As expected from the HSTS design studies, the impulse response of these DOFs reveals that without other local damping (say from optical levers), the highest V and R modes (at 9.7 and 13.8 [Hz]) get excited when the PUM and TST are kicked, and continue undamped at their original extremely large Q. 
 - If needed, both the fundamental V (at 0.55 [Hz]) and R (at 0.86 [Hz]) could use an increase in their resonant gains to decrease the 1/e time for those modes, which seem to dominate the amplitude of the time series for the initial 10-20 seconds. V would be much easier than R, as the LUGF phase margin for R is already pretty small.

In P, 
 - As with the HSTS, the global control transfer functions are barely affected by the differences in design, though -- to be fair -- the differences in design are much less dramatic than in the HSTS. 
 - Test mass impulse times are comparable.
 - The first "pitch" mode at 0.51 [Hz] is more damped (by about a factor of ~2) in the LHO model because of the increase in overall gain. However, since the second mode at ~1 [Hz], is more L motion at the test mass than P, increasing the gain at this frequency by a factor of 5 with the "resg1" in the L design seems to have reduced this "P" mode by the same factor at the test mass. Interesting!
 - The notch at 60 [Hz] has little affect on the loop design -- I suspect this was installed to kill a ground-loop feature in a particularly bad OSEM.

In Y,
 - This is pretty straight forward -- the yaw loop is not particularly limited in phase margin, only in noise re-injection. If we're willing to sacrifice a factor of 4 in noise, cranking up the gain reduces the impulse response by 4, and the Qs of the global transfer functions.

I could easily enage the ISS second loop, following the procedure described in 14291. It worked without problems.

However, the loop performances were very poor, as shown in the first plot. The dashed lines corresponds to the second loop open, the solid lines to the second loop closed. The inloop signal is squeezed down to a reasonable level. However, we're getting only a factor 10 of out-of-loop noise reduction. This is much worse than in the past.

I could improve a bit the situation re-centering the beam on the ISS QPD: it was quite far away. The second plot shows that the loop performance is improved, but still worse than what we got in the past. The thrid plot compares in-loop and out-of-loop signals when PD1-4  or PD5-8 are in loop. There is no significant difference, so it's not only one of the two PD sets to be misaligned.

Tomorrow I'll need to play again the picomotr game to recenter the photodiodes. The last centering was performed more than one month ago, on October 3rd, and then there has been no activity around the ISS, as far as I know. Therefore, it's maybe not surprising at all that the alignment is no more optimal. The IMC alignment might have changed.

Offsets tuning

Today I set down again to improve the  working point of the IMC angular controls, ina  way similar to waht I did in the past (see here)

The first step was to histogram the band-limited RMS noise of the ISS second loop photodiodes, to measure the dependency of the RIN on the residual angular motion of the IMC. The first attached plot shows the BLRMS between 200 and 1000 Hz, histogrammed against the six IMC degrees of freedom. It is apparent that there are offsets in almost all signals. The offset is particularly evident in DOF_1_Y. Fo future reference, the period considered is between 10.21 and 10.42 local time.

Using these histograms, I finely tuned the following offsets (which are different from what was running before):

The second attached figure shows the improved histograms after this tuning. The third plot shows the reduction in the noise as seen by the ISS second loop (sorry, the plot is not calibrated in units of RIN). For future reference, the period considered is between 11.10 and 11.29 local time.

The intensity noise is however still clearly non stationary and the fluctuations seem loosely related to the residual motion of the IMC degrees of freedom.

After some other activities, reported below, I had the impression that the alignment was not more optimal (higher noise in the ISS diodes). I checked again the offsets and it turned out that setting DOF_3 to zero did improve the noise. Therefore I suspect that some of the offsets are not very stable over time.

Calibration lines to check drifts

To track more accurately those possible drifts, I added two lines on the PZT: pitch at 155 Hz (amplitude 3) and yaw at 247 Hz (amplitude 3). My goal is to leave these lines on all night and then use them to reconstruct any variation of the jitter to RIN coupling.

PZT noise injections

FInally, I injected some broad band noise in the PZT, to measure the transfer functions to the IMC signals. Here are the times

PZT pitch amplitude 30, elliptic band pass 10-550 Hz: from 12.20 to 12.27 local time
PST yaw amplitude 30, elliptic band pass 10-550 Hz: from 12:28 to 12:34 local time

Increasing DOF_1_Y gain

The histograms hinted at the fact that the fluctuations in the RIN were correlated to DOF_1_Y. I measured its open lop gain and the unity gain frequency was about 60 mHz. I increased the gain by a factor 4, thus moving the UGF to a bit more than 200 mHz. See fourth plot. However, this did not produce any significant improvement in the intensity noise. This is consistent with the idea that most of the coupling is due to "fast" motion of the input beam.

• LVEA in bifurcated state this morning until noon
• 3IFO crew transfering SUSpensions in LVEA
• 8:42--Jodi heading out to check on 3IFO work
• 8:45-8:58--Jim heading out to LVEA to search for parts
• RE-booting projector computers (Jim B)
• 9:19  EX PEM cabling (Filberto/Aaron)
• 10:03 OFI measurements in H2 enclosure (Gerardo)
• 11:09-12:27 Measurements on floor at racks near H1 PSL (Dick)
• 3ifo crew cleared out of LVEA before noon
• 12:07 EY ALS work on green path; they did multiple trips (Nic & Evan)
• 2:09 Andres/Jeff moving OFI parts briefly

Nic, Evan

We went down to EY to see what was up with the green WFS on ISCTEY (D1400241). To start with, we decided to resteer the beams so that they are not clipping on any optics.

• We steered M14 so that the beam passed through the clear aperture of BS5 (before it was exiting too close to the BS mount).
• We resteered onto PD8 by touching L9 and L15. We got a factor of 10 more dc power on the PD this way.
• We moved M16 (a piezo mirror) slightly so that the beam is centered on the mirror, and so that it travels to M18 (also a piezo mirorr) parallel to the hole pattern on the table.
• We moved BS6 and L12 so that the beam passes cleanly through these optics.
• Using M17, we resteered onto WFS A.
• We moved L13 so that the beam passes through cleanly.
• Using M19, we resteered onto WFS B.
• We moved the iris between M14 and BS5 so that the splotchy beam from the Faraday isolator can be stopped down to something vaguely circular.

We also tightened down PD4, which had some issues with loose mounting.

Jeff B and crew (Andres, Mitchell, Joe D, Chris S) and grounding plugs to and loaded eight of the nine HXTS and the OMC into the modified HAM ISI storage container this morning. The work went more quickly than we estimated. 

Upon taking a look at all large suspensions and small suspensions aux channels only ETMY stage L1 was found to have a noise aux channel which is showing some possible issue. ie ~ -4300 cts. This is showing on "noise" (4), volt (UL) and fast_I (LR). I have begun setting up DTT templates for all aux sus channels to further examine questionable readings.