This afternoon, the absorption measurement on the WI mirror has been performed.
The ITF locked at CARM null at 11.48 UTC, the HWS-INJ acquisition started at 13.32 UTC (20230528T1532). After 10 min, 13.42 UTC (WF 21), the ITF was unlocked in the ‘gentle’ manner. Unfortunately, the gentle unlock did not work: the CH flip mirrors opened (but I immediately closed them) and Fabio manually re-aligned PR and WI. He restored the alignment of the mirrors at 13.47 UTC (WF 26). Thus, the WFs immediately after the unlock (23-26) are not reliable.  At 15.21 UTC (WF 201), the CH has been switched ON at nominal value and the HWS-measurement has been interrupted.  

ANALYSIS

• POINT ABSORBERS

Since the first WFs after the unlock are not reliable, a new measurement is needed to exclude their presence.

• YAG POSITION IN THE HWS MAP

The YAG-induced OPL at different times are shown in figure 1.

The barycenter coordinates vs Time are shown in figure 2.

The YAG barycenter coordinates have been evaluated from the steady state maps (from WF100 to WF200):

• YAG CURVATURE EVALUATION

The Gaussian weighted curvature is shown in figure 3.

The average curvature of 28th May has been multiplied x548 mW/567mW, where 548 mW is the B8 value during the measurement performed on 28th March and 567 mW is the value measured today before the unlock (figure 4).
 From this measurement, no evidence of the WI absorption change is visible. 

• CH POSITION IN THE HWS MAP

The HWS maps have been re-analyzed using as reference the last WF before switching ON the CH (WF 200). An example is shown in figure  5.

The barycenter coordinates vs Time are shown in figure 6.

The CH barycenter coordinates have been evaluated from the steady state maps (from WF 250 to 381):

• CH  CURVATURE EVALUATION

  The Gaussian weighted curvature is shown in figure 7.

Conclusions:

-WI absorption did not change

-YAG and CH appear well aligned

-PAs to be investigated with a new measurement