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AdV-COM (AdV commissioning (1st part) )

mantovani, cesarini, lorenzini - 14:56 Friday 18 October 2019 (47276)

Summary of the 17th morning shift

Yesterday morning we have started the tuning of the DAS actuators following this procedure:

starting point: CMRF = -0.4e-9; 112MHz mag = 0.081; CD = 19;

- 1st step: increase of the sideband power using the WI outer ring (from 170 mW to 200 mW)

CMRF = -0.5e-9; 112MHz mag = 0.087; CD = 18.4;

- 2nd step: decrease the CMRF using the NI outer ring (from 2.36 W to 2.41 W). This tuining is not differential thus the common mode (the one that maximise the sidebands) is spoiled and has to be compensated

CMRF = -0.12e-9; 112MHz mag = 0.083; CD = 18.6;

- 3rd step: increase back the sidebands using the WI inner ring (from 154mW to 124 mW)

CMRF = it was @ LN1. 112MHz mag = 0.085; CD = 18.6;

the trend is visible in Figures 1 and 2 to highilight the pourpouse of the actuator tuning).
Figure 3 shows the tuning to reduce the CMRF.

Images attached to this report

Comments to this report:

mwas - 15:43 Friday 18 October 2019 (47279)

In addition to the 56MHz sideband gain, the B1p power / contrast defect, and the CMRF, the power on B1s2 when in LN3 is an important figure of merit. The B1s2 power when both OMCs are locked is dominated by the 56MHz TEM01 mode, which causes OMC lock acquisition issues and couples the 56MHz RAM to the sensitivity. From that perspective the best state was at around 9UTC with about 0.075mW, this is better that other times, but still higher than the 0.05mW we had during O3a.

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