This evening we performed some sine injections on SDB1 and SWEB benches in order to measure the back-scattered light coupling transfer functions. We did these measurements both in Low Noise 2 and Low Noise 3 in order to check the impact of the SR alignment.
1/ Noise injections in Low Noise 2:
Reference data taken in Low Noise 2 from 18h11 utc to 18h15 utc.
1.1/ Noise injection on SDB1 (by acting on the suspension top stage F0):
We apply a sine function at 0.1 Hz, with an amplitude set to 0.2 in the damping interface, which corresponds to a bench motion of +/-5 um at ~18h17.
Amplitude increased to 0.4 at 18h19m30, bench motion of +/-10 um.
Amplitude increased to 0.7 at 18h21m40 utc, bench motion of +/-17 um. We start to see an effect on the sensitivity curve (see Fig.1). Glitch at 18h22m50. We collect data until 18h27 utc.
1.2/ Noise injection on SWEB (acting on SBE top stage):
We start injecting a sine function at 0.2 Hz, with amplitude set to 1 in the SBE config file at 18h39m56 utc: no clear effect on the bench position.
Amplitude increased to 50, at 18h42m40 utc, corresponding to bench motion of +/-6 um.
Amplitude increased to 100 at 18h44m50 utc, corresponding to bench motion of +/-12 um, still no clear effect on the sensitivity.
Amplitude increased to 150 at 18h49m39, corresponding to bench motion of +/-20 um. We can observe the noise coupling in the sensitivity curve (see Fig.2). Glitch at ~18h52. Injection stopped at 19h08 utc (we observed an intermediate glitch but did not write the time).
2/ Noise injections in Low Noise 3:
Reference data taken in Low Noise 3 from 19h21 to 19h26 utc (5 min).
2.1/ Noise injection on SDB1 (from F0 stage):
We apply a sine function at 0.1 Hz, with an amplitude set to 0.7 in the damping interface, which corresponds to a bench motion of +/-17 um at ~19h28m46 utc. Glitch at 19h32m30 utc. Taking data until 19h37 utc. See Fig.3
After stopping the SDB1 injection, we wait for the sensitivity curve to come back to normal noise level below 20 Hz. Then we collect some reference data from 19h45 utc (4 min).
2.2/ Noise injection on SWEB (from suspension top stage):
We inject a sine function at 0.2 Hz.
Start injection at 19h49m26 utc, with amplitude set to 50, corresponding to a bench motion of +/-6 um.
Amplitude increased to 100 at 19h51m29 utc, corresponding to +/-13 um. Collecting data until 19h57 utc. Fig.4
2.3/ Noise injection SDB2:
As a check, we performed another injection on the SDB2 bench with a frequency line at 0.1 Hz.
Start injection with amplitude set to 10 at 20h03m17 utc, corresponding to bench motion of +/-3 um.
Injection increased to 50 at 20h05m19 utc, corresponding to bench motion of +/-14 um.
Injection increased to 75 at 20h07m38 utc, corresponding to bench motion of +/-20 um. Stopped injection at 20h14m50 utc. See Fig.5