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On-site interventions (General)
melo, chiummo - 9:47 Sunday 04 April 2021 (51314) Print this report
INJ on safety mode and check DET ERoom Temperature

After receiving the warning about the Timing issue (#51308) last night, I came on site this morning to put the INJ system in safety mode.

For that, we opened the BPC loop, put the PMC in scan and blocked the beam in the output of the laser bench.

Moreover, we noticed that the flag ACS_DET_ALARMED - mean_INF__DER_TE_80 was almost at 35 deg, and I tried to solve the issue by opening the door of DET_ERoom. However, the action did not seem to have produced any visible effect. Since the temperature was already decreasing by itself I closed the door again when I left.

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derossi, gosselin, bulten, chiummo, spinicelli - 17:24 Tuesday 06 April 2021 (51332) Print this report

The system has been recovered this afternoon.

One of the actuators of the EIB suspensions was out of range and we called Henk Jan to recover it.

Then we had to manually realing the beam with EIB M4 and M8 mirrors in order to be able to close the beam pointing control loop. Once the BPC was closed, we set the old values for the SIB1 and MC positions but the IMC was not locked yet. The references for the MC had slighlty changed and we had to move a little bit MC TX in order to lock the mode cleaner (attached plot).

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ruggi - 20:08 Tuesday 06 April 2021 (51334) Print this report

The alignment of the arms required a relevant vertical shift of PR mirror, with respect to the latest nominal position: about 400 um. There is nothing in the suspension behaviour which can suggest that the setting of the vertical sensors should have been changed in order to recover the same vertical position, so one would conclude that the position of PR is actually different (but we cannot be sure). If this is true, one possible explanation is that the beam coming out from SIB1 has changed the vertical inclination by about 50 urad.

This is not a concern at all regarding PR suspension control, or PR centering accuracy. It is just to ask if the intervention done in order to recover BPC could have determined or not such a beam rotation.


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