AdV-COM (AdV commissioning (1st part) )swinkels, hoak - 16:30 Tuesday 21 February 2017 (36608)
Print this reportComment to PRC length measurements -- MICH offset reduction in steps (36576)Some additional info related to the phase measurements. Fig 1 shows signals from the lock of the CITF on the carrier, while Fig. 2 shows the same for the lock on the sidebands. To estimate the correct demodulation phase, we take the actual value (SPRB_B2_6MHz_phi0) and subtract the demodulation phase error (LSC_B2_6MHz_DPHI) measured using the PRCL line. For most of the lock on the carrier, the estimated phase was pretty stable at 0.11 rad. After optimizing alignment (around 18:40 UTC), it might have increased a bit to around 0.16 rad. For the lock on the sidebands, the measured value was fluctuation, probably due to alignment. Assuming that the CITF was reasonably aligned around 18:50 and 20:15 UTC, the optimal phase should be 0.21-0.22. This suggests a phase difference between 0.05 and 0.1 rad. Using Dan's value of 0.8 deg/mm and Jerome's value of 0.9 deg/mm, this would correspond to a length mismatch of 4 to 8 mm (with unknown sign). To be understood in similation how much we can tolerate. To get a more accurate estimate, we would likely need a working alignment scheme.
