This afternoon, we continued the shift that started on Tuesday, July 22nd (entry 67353).
The CO2 PA was projected onto two different points on the HR surface along the horizontal direction.
Summary of actions:
-15:10 UTC — Manual unlock of the interferometer performed in order to transition the ITF to LN2 mode.
- 15:19 UTC — CO2 laser switched ON.
- 15:44 UTC — ITF reached LN2 mode.
The reference image of the thermal camera without NO CO2 PA is shown in Fig.1.
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CO2 PA applied in POSITION 1 (see Fig. 2).
Approximately 15 mW were applied to the HR surface of the mirror. Let us underline that the power was very unstable due to the difficulties of the chiller to keep the working point (see Fig.3). To improve stability, two options could be considered: shortening the tubes connecting the chiller to the laser, or using the TCS chiller.
16:27 UTC — Start shining →TCS_IPATSIA_REL1 = 0
16:42 UTC — Stop shining →TCS_IPATSIA_REL1 = 1
No evident effects were observed on the main ITF signals during the shining (see Fig.4).
Subsequently, in order to increase the CO2 power injected into the ITF, I accessed the tower base. During this operation, the ITF unlocked at 16:49 UTC (unclear whether related). Later, during the OMC locking phase, the ITF unlocked again at 17:18 UTC. Piernicola identified an unusual oscillation of the EIB after the unlock. He resolved the issue, allowing the re-locking sequence to proceed.
The ITF successfully re-locked in LN2 mode at 18:27 UTC.
At 18:31 UTC, we applied CO2 PA on the HR surface with the PA still in POSITION 1, but using increased power compared to the previous attempt, 40 mW (see Fig. 5).
At 18.53 UTC, we switched it off.
In this case the effect was clearly visible in the ITF signals (see Fig.6 )
Ten minutes after switching it off, we adjusted the horizontal position of the CO2 PA by acting on the steering mirror.
2. CO2 PA applied in POSITION 2 (see Fig.7)
At 19.09 UTC, the CO2 PA shined the HR-surface.
At 19:31 UTC, the CO2 PA was switched off.
The main ITF signals recorded during the shining period are shown in Fig. 8.
Ten minutes after switching off the CO2 laser, we carried out all the necessary operations to safely shut down the entire setup.
At 20:02 UTC, the ITF was in LN3 and Science Mode.
