Today, we continued the activity that started in 67723.
This time, the CO₂ PA was shined on the WE to perform the vertical scan in LN2 (and not in LN3 with the SR partially aligned).
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10:41 UTC – Switched on the chiller at 19°C and the CO₂ laser.
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14:00 UTC – ITF manually unlocked from LN3 (after putting commissioning). Shortly after, an earthquake prevented the relock for some time.
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17:21 UTC – Relocked in LN2.
Position 2 (as in Figure 1, same as entry [67723]):
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17:44:40 UTC – Flip mirror opened.
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18:23:00 UTC – Flip mirror closed.
Position 1 (as in Figure 2, same as entry [67723]):
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18:37 UTC – Changed PA position onto the test mass.
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18:39:51 UTC – Flip mirror opened.
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19:15:01 UTC – Flip mirror closed.
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At 19,21 UTC, we put the ITF in LN3.
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At 19.43 UTC: we start to shine the CO2 PA in LN3 (in Position 1)
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At 20.06 UTC we closed the flip mirror and switched off the CO2 laser.
When we operated in LN3, we experienced some instability in the CO₂ power due to temperature variations. A tuning of the chiller setpoint would have been required,
but there was no time to perform it. As a result, during the shining period we did not have a constant CO₂ PA power.
The behaviour of the CO₂ laser during the shift is shown in Figure 3 and the main ITF signals are shown in Figure 4.
Concerning the LN2 measurements:
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In Position 2, B7/B8 power decreased by ~3 %, optical gain decreased by ~1 %, and BNS range decreased by ~10 % w.r.t. nominal condition.
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In Position 1, B7/B8 power decreased by ~7 %, optical gain decreased by ~3 %, and BNS range decreased by ~6 % w.r.t. nominal condition.
