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AdV-COM (Flat noise)
mwas, bersanetti, rolland - 13:17 Monday 02 December 2019 (47831) Print this report
DARM offset reduction and sign change

7:30 UTC (30min) reference time in Science mode

around 8:05 UTC unlocked due to mistake (reducing DARM offset without a ramp)

relocked at second attempt

8:42 UTC (5min) reference time after relock (same range as before unlock)

reduced dark fringe offset

9:00 UTC (5min) dark fringe offset at 1mW per B1 PD (instead of 2mW) and Hrec has adjusted the optical gain. DARM_SET=0.00032 and DARM_GAIN = 12.0

improved BS TY and TX alignment to reduce CD (contrast defect on B1p)

9:15 UTC (5min) range is worse with this alignment, noise is higher from 50Hz up to a few kHz, ITF optical gain goes down by 1%

put back initial alignment

9:25 UTC (10min) good data with dark fringe offset at 1mW per B1 PD

going back to nominal dark fringe offset

9:45 UTC (10min) good data with dark fringe offset at 2mW per B1 PD

Relocking with negative DARM offset, change the offset sign in ITF_LOCK.ini, the sign of DARM demodulated OMC signals and sign of B1 in Hrec_hoft (keeping HrecClean_hoft with nominal sign for comparison)

Figure 1 shows the range, dark fringe offset and BS alignment signal trends, the reduced dark fringe offset may have a small impact of improving the range by ~1Mpc, but it is hard to say the range itself fluctuates by +/-2Mpc.


10:18 UTC relocked with a negative dark fringe offset, sensitivity is bad due to a bad alignment working point

Adjusted the DIFFp and BS working point, h(t) and CD don't agree on what is the best alignment point (it was already the case for the positive dark fringe offset)

11:00 UTC (12min) data with optimized alignment working point

Figure 2 shows the HOM on B1 with 1mW of positive dark fringe offset and Figure 2 with 1mW of negative dark fringe offset. The HOM content is different. In the latter we have seen that the SDB1 angular offset has not much impact on the range, unlike what we have seen with the positive offset a month ago. To be checked on the camera images if there is no impact of the SDB1 angular offset on B1 HOM shape with a negative offset.

between 11:12UTC and 11:27 UTC tried SDB1 vertical alignment offsets, not much impact on the range and with zero offset close to optimal ITF gain

lowered DARM offset to -0.00032 with DARM GAIN at 12.0

11:35 UTC (14min) good data with lowered dark fringe offset, 1mW per B1 photodiode

adjust SDB1 horizontal alignment offset, no impact on the range

Going back to the nominal configuration (DARM offset positive, and 2mW per B1 photodiode).


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Comments to this report:
mwas - 16:30 Monday 02 December 2019 (47837) Print this report

A look at how HOM depend on global alignment, summary

  • The HOM shape does not seem to depend on the global ITF aligment
  • The HOM shape is differnet on both side of the dark fringe offset
  • The HOM power depend on the SDB1 vertical aligment
  • The HOM pattern rotates with an SDB1 horizontal aligment
  • The vertical and horizontal dependence points to a vertical mode, to explore it more one would need to act both on the SDB1 vertical alignment and displacement.

Figure 1 shows the trend of signals during the time with positive dark fringe offset. We will focus here at the time with 1mW per B1 photodiode, and in the middle around 9:15 UTC there is the change in BS set points which increases the transmission of the 56MHz order 1 mode (higher B1s2 power).

Figure 2 shows the HOM before the BS alignment change, Figure 3 during the change in BS alignment, and Figure 4 after restoring the original aligment. There is no clear change in the HOM, but the central saturated blob has a more elongated shape when the B1s2 power is higher due the 56MHz order 1 mode.

Figure 5 shows the trends during the time with negative dark fringe offset (first with 2mW and then 1mW per B1 PD)

Figure 6, 7, 8 and 9 show images during the ITF realignment, there is no significant change in the HOM content

Figure 10 shows the image with a positive vertical offset on SDB1, and figure 11  with a negative. On figure 10 the HOM is much reduced in power, and figure 11 it is much increase in power. Unfortunately, the case with less HOM, corresponds to more 56MHz order 1 mode transmitted as visible on B1s2 and the elongation of the saturated central blob on B1.

Figure 12 shows data with 1mW dark fringe offset, 13 with a positive horizontal SDB1 angular offset, and 14 with a negative horizontal SDB1 angular offset. The power of the HOM doesn't change much, but especially when comparind figure 13 and 14 the pattern rotates.




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