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AdV-ISC (Commissioning up to first full interferometer lock)
boldrini, magazzu - 17:08 Sunday 14 August 2022 (56753) Print this report
ISC shift: SR RH + CHRoCC study

We repeated the study of the matching for different values of the CHRoCC power, for the new value of the SR RH power. Since reducing the CHRoCC power seemed to be the most promising direction in the past few days, we took data for 0.43 V -> 0.41 V -> 0.39 V of CHRoCC power. The following table recaps the GPSs of each data gathering:

 

CHRoCC power DRMI Reference

Long Arms scan
(FSR + TEM2)

 DRMI Scan OMC
Scan
0.43 V UTC:8:34:00
(5mins)		 UTC:07:11:00 UTC:9:20:30
(6 scans)		 UTC:8:56:00
0.41 V UTC:11:14:00
(5 mins)		 UTC:11:54:00 UTC:11:43:00
(5 scans, unlock during last ramp down)		 UTC:11:21:30
0.39 V UTC:14:14:30
(5 mins)		 UTC:13:44:00 UTC:14:32:00
(3 scans, unlock during the first ramp up)		 UTC:14:49:30

 

Before taking the first reference of the DRMI, we verified that phases and gains of the DRMI were correct (PR_AA, BS_AA, PRCL,MICH,SRCL in 3f). Only the phase of the 18MHz signal for PR_AA had to be tuned from -1.05 rad to -0.7 rad. After taking the first reference for the DRMI, we also took 120s of data with the LF line of the NI pumped to ampl: 6e-4, to be used for further comparisons between the simulated and actual alignment sensing. The GPS for this measurment is:

UTC:8:47:30 +120s

Notice that we relocked the arms to reset the alignment of the mirrors once per 30-40 minutes on average. The SR was praligned at each lock of the DRMI. The first and third points of the measurements were timed with two distinct earthquakes, one in China and one in the Pacific Oceans. They were not strong enough to cause any significative distruptions, but the CITF was more fragile during the CARM_SET ramp and we could only perform 3 ramps (in particular, the DRMI unlocked during a ramp up but relocked on its own at CARM_SET = 32250 Hz, the following three ramps down-up-down were smooth, the third ramp up unlocked the DMRI again, Fig.1). The unlocks of the DRMI were very sudden, and do not offer clear explanations as why some ramps successfully arrive at the end while some do not.

Please refer to the operator entry for the plots relative to today's scans.
 

Images attached to this report
Comments to this report:
mwas - 16:36 Monday 15 August 2022 (56756) Print this report

Summary

  • The OMC scans don't show any clear direction on the CHRoCC tuning, but clearly the situation is worse with SR RH at 2.8W wrt to 6W (Aug 12).
  • On the phase cameras the dependence with CHRoCC tuning seems the same at SR RH 2.8W, but with a worse overlap, especially for lower CHRoCC powers.

Figure 1 shows an overview of the analysis of the OMC scans with SR RH at 2.8W, with the SR RH power from Aug 12 with 0.43V on the PR CHRoCC as a reference. One surprise is that there is lots of background light on B1 PD3 for the case 0.39V on the CHRoCC, at least 10 times more that in the other cases. I would assume it is not related to the CHRoCC tuning, but I have no idea where this is coming from. Also the change in SR RH power means that the detection telescope is detuned, and the OMC mode mismatch is expected to be about 10%. So the result below are not very reliable, and not reliable at all for any effect at the 10% level or less.

Figure 2, 3 and 4 are the oder 0, 1 and 2 peak height for the 56MHz USB, and figure 5, 6 and 7 are the order 0, 1 and 2 peak heights for the 56MH LSB.

The USB TEM00 is again increasing with lower CHRoCC power, by 60% , but this time the USB order 2 mode is also increasing in power, by 30%. So the mode shape is not improving much. And in all cases it is worse than the reference with 6W on the SR RH.

The LSB TEM00 doesn't show a clear trend with CHRoCC power, and in all cases is lower than the reference from Aug 12, by 30% or more. And the order 2 mode is decreasing in power, by 30% after two steps, but this is the same change as the TEM00. So there is no improvement in mode shape.

Figure 8, the 56MHz power on the B1p and B4 PC looks the same for both cases of SR RH power level. But the USB vs LSB overlap looks worse at 2.8W instead of 6W on SR RH. Especially the overlap on B4 looks worse.

Figure 9, 10 and 11 show the B1p and B4 PC images for the three CHRoCC settings. The beam shape on B4 seems again to be improving with less CHRoCC correction, with the beam loosing a side lobe.

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