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mantovani - 10:23 Wednesday 25 January 2023 (58548) Print this report
long term behaviour of QD* 25MHz signals

I've analyzed the trend of the 25MHz signals (both QD1 and QD2) during the CARM 0 lock of the last week, while the SR is closed with the DCP signal.

The trend is visible in Figure 1. The offset between the DCP and the 25MHz is not constant and depends strongly on the alignment of the other DOFs such as BS and DIFFp (at it was also expected).

Moreover there is a strange behavior occurred yesterday that has to be analyzed (see third ellipse in the plot).

 

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mantovani - 15:02 Wednesday 25 January 2023 (58554) Print this report

The strange event, highligthed with the third ellipse, is due to a malfunctioning of the QD1 galvo (which was off), see Figure 1.

It is important to highligth that this QPD is used also for BS. Luckily not too strange behavior was visible on BS control, see Figure 2.

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mantovani - 11:05 Tuesday 31 January 2023 (58636) Print this report

Collecting more data, it is visible that the 25MHz error signal zero varies wrt the DCP SR wp.

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mantovani - 14:48 Tuesday 31 January 2023 (58644) Print this report

Using the excitation line of SR the calibration of the error signals have been measured as QPD1/2_h/v/SR_MIR_ty/tx|_exc_line.

the values found are:

qd1h/SR ty= 2.9e-4; qd2h/SR ty = 6.5e-5;

qd1v/SR tx = -3.5e-4 ; qd2v/SR tx = 1.4e-4;

we can then calibrate the offsets between 25MHz QPDs signal and the SR DCP signal, see Figure 1, which is not negligible.

I' m then studying if the combination of the two can give a signal for SR (some tests are needed).

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