Yesterday evening (Oct 03) I injected again a sine motion at 0.1 Hz on SNEB and SWEB benches in order to investigate the reason for the extra scattered light observed on SNEB with respect to SWEB (entry 47072). One plausible hypothesis is that this scattered light may come the light back reflected by the quadrants, since there are beam dumps blocking this light on SWEB, but not on SNEB. Therefore, two different conditions were tested: bench moving with quadrant shutters open and close. The list of measurements is provided below.
SNEB injections:
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Reference data with B7 QD shutters closed : 19h46m30 utc – 19h52m00 utc
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QD shutters closed: Injecting line on SNEB, amp = 30, bench moving by +/-9 um, starting at 19h53m30 utc (3 min)
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QD shutters closed: Injecting line on SNEB, amp = 60, bench moving by +/-18 um starting at 19h56m45 utc (3 min)
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QD shutters open: Injecting line on SNEB, amp = 60, bench moving by +/-24 um, at 20h01m20 utc (3 min)
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QD shutters open: Injecting line on SNEB, amp = 80, bench moving by +/-24 um, at 20h05m20 utc (3 min). See Fig.1
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QD shutters closed: Injecting line on SNEB, amp = 80, bench moving by +/-24 um, at 20h09m00 utc (3 min). The DARM spectrum at the time of this injection with shutters closed (blue) is compared to the time of the injection with shutters open (purple) in Fig.2. It seems that the scattered light is larger with the shutters closed.
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Reference data with QD shutter closed: 20h13m00 - 20h16m00
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Reference data with QD shutter open: 20h16m30 - 20h19m30
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B7 QD shutter closed at 20h19m40 utc.
SWEB injections:
- Reference data with B8 QD shutters closed : 20h20m00 utc – 20h25m00 utc
- QD shutters closed: Injecting line on SWEB, amp = 150, bench moving by +/-20 um at 20h26m30 utc (3 min), Fig.3
- QD shutters open: Injecting line on SWEB, amp = 150, bench moving by +/-20 um at 20h30m05 utc (3 min), Fig.4
- QD shutters closed: Injecting line on SWEB, amp = 150, bench moving by +/-20 um at 20h34m05 utc (2 min)
SDB1 broad band injections:
Then broad band noise was injected on SDB1, along the Z axis, in order to excite high frequency resonances:
- Injection with SDB1_LC_Z_Corr = 2.0 e-3 V/sqrt(Hz), at 20h42m20 utc (1 min 30)
- Injection with SDB1_LC_Z_Corr = 4.0 e-3 V/sqrt(Hz), at 20h44m25 utc (2 min), Fig.5
- Injection with SDB1_LC_Z_Corr = 8.0 e-3 V/sqrt(Hz), at 20h46m45 utc (30s), Fig.6. The ITF unlocked at 20h47m16 utc, because of NI DSP fail.
Further analysis will be performed later.
