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AdV-DET (Commissioning)
demagny, gouaty - 19:04 Thursday 31 October 2024 (65440) Print this report
Scattered light noise measurements on the suspended benches

This afternoon we excited the suspended benches SDB1, SDB2, SQB1, SWEB and SNEB in order to measure the scattered light noise coupling factors.

Activity starting at 12h45 utc with ITF locked in Low Noise 3 SQZ.

We collect reference data from 12h45 to 12h52 utc.

1/ Injections on SDB1:

We switch off SDB2 tracking at 12h56m06 utc. We then observe a large excess noise on hrec (Fig.1)

Tracking on at 13h02m50 utc. After the reengagement of the tracking the noise cut-off frequency was reduced by ~200 to ~100 Hz but the excess noise is still present below 100 Hz. In fact we noticed that the corrections sent to the SDB2 suspension were going out of range. So we disengaged the SDB2 suspension loop at 13h05m45 and reactivated them at 13h05m49 utc. The Hrec spectrum is back to normal at ~13h14 utc.

Starting injection of a line at 0.1 Hz on Sa_OB_F0_X with an amplitude of 0.2 at 13h14m45.

Increase amplitude of the line to 0.5 at 13h17m36 utc: this corresponds to a bench motion of +/-12 um. We see a noise coupling at low frequency, below 25 Hz, see Fig.2. Injection stopped at 13h24 utc.

Increase amplitude of the line to 0.7 at 13h27m05 utc: this correspond to a bench motion of +/-17 um. However the SDB2 bench is also moving by +/-20 um because of the tracking loop. See Fig.3. Injection stopped at 13h35 utc.

2/ Injections on SDB2:

We start by injecting a line at 0.1 Hz on SBE_SDB2 with an amplitude of 10 (bench moving by +/-3 um) at 13h43m50 utc.

We increase the amplitude of the line to 50 (bench moving by +/- 13 um) at 13h51m30 utc.

We increase the amplitude of the line to 75 (bench moving by +/- 20 um) at 13h54m47 utc. Warning there was a glitch around 13h58 utc. We start again the data taking at 13h59 utc ( see Fig. 4). Injection stopped at 14h07m36 utc.

3/ Injections on SQB1:

3a/ With ITF in LN3_SQZ:

SQZ_PLL AA dither control disabled at 14h20m19 utc.

Inject line at 0.1 Hz on SQB1 with amplitude 10 at 14h23m19 utc: bench moving by +/-4 um.

Amplitude increased to 50 at 14h25 utc: bench motion of +/-18 um. Periodic glitch at 14h27 utc.

Amplitude increased to 75 at 14h28m02 utc: bench motion of +/-27 um. See Fig.5. Injection stopped at 14h34m22.

AA dither reengaged at 14h35m06 utc.

We inject the line with amplitude 75 at 14h39m40: in this case this produces a weird excess noise on Hrec (see Fig.6) probably caused by the AA dither. We stopped the injection at 14h40m24.

3b/ With ITF in LN3:

Nicola disengages the squeezing upon our request at 14h44 utc.

We collect data for reference from 14h45 to 14h50 utc.

We inject the line on Y instead of Z with amplitude 75 at 14h51m51: We first observe a large excess noise than the bench is stabilized at +/-5 um. Periodic glitch at 14h54.

We try to disable the AA dither at 14h55m38, no effect. We then realize that the line was not injected on the right dof. AA dither enabled back at 14h57m12 utc.

Taking data with AA dither engaged, line injected with amplitude 75 (bench motion of +/-27 um). See Fig.7. Injection stopped at 15h03m01 utc. WARNING: after checking the data we realized that the vertical position loop of SQB1 has been misbehaving since the accidental injection on Y. Thus this measurement is not very reliable.

Nicola restore the LN3_SQZ at 15h05 utc.

 

4/ Injection on SWEB:

We collect reference data from 15h12 utc to 15h17 utc.

We inject a line at 0.1 Hz with amplitude 50 at 15h18m25, which correspond to a bench motion of +/-10 um. No impact on Hrec.

Amplitude increased to 100 at 15h21m44 utc (bench motion of +/-18 um). Glitch at ~15h22 utc. Collecting data from 15h23 to 15h28. Sensitivity shown on Fig.8.

Frequency of the line increased to 0.2 Hz (bench motion of +/-13 um) at 15h28m10. See Fig.9. It seems that we see the double bounce at ~60 Hz.

Amplitude of the line increased to 120 at 15h33m56 utc (bench motion of +/-16 um): See Fig.10. The presence of the double bounce is not obvious at all. Maybe this was an artifact.

Injection stopped at 15h41m07 utc.

 

5/ Injection on SNEB:

At 15h49 we turn off the the highbandwidth control of COMMp.

We inject a line at 0.1 Hz with amplitude 50 at 15h51m21 utc, corresponding to bench motion of +/-5 um. Periodic glitch at ~15h52m04 utc.

We increase the line amplitude to 100 at 15h53m27 (motion of +/-11 um).

We increase the line amplitude to 150 at 15h54m58 (motion of +/-17 um). See Fig.11.

We increase the line frequency at 0.2 Hz at 16h00 utc (motion of +/-16 um). See Fig.12.

Injection stopped at 16h07m31 utc.

After this injection was stopped, the bench remained excited and the ITF finally unlocked as the position loop opened.

We retored the highbandwidth control of COMMp.

 

During the ITF relock, we noticed that the B5_QD1_V galvo correction was very large when arriving in CARM_NULL_1F. So we reduced a bit the correction by ~2V with +250 steps on B5_M1V.

The ITF unlocked at 16h52m44 utc due to an increase of power on B1s that triggered the fast shutter closing (Fig.13).

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