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AdV-TCS (Ring Heater)
cifaldi, mantovani, melo, spinicelli, taranto - 8:14 Wednesday 13 July 2022 (56432) Print this report
DET-HWS beam centering

Starting from the entry 56420, the goal of yesterday shift was to continue the centering of the DET-HWS beam on the NI. We decided to proceed by using the RH curvature center position, we knew that it would be longer but it is more reliable.

Then, at 09.09 UTC we switched on the NI RH @ 15 W and we noticed that the RH curvature center becomes quite stable after the first hour of the transient (see figure 1). 

We started to investigate the cause of this movement by looking at the NI local control signals, see figure 2.

Piernicola performed some movement with the NI to see the effect on the HWS sensor (see figure 2). The effect of the tilt is clearly visible on the wavefront, but a tilt of about 5 microradiants generated an effect less visible with respect to the movement performed in the first hour of the transient (see figure 3). The entire behavior of the coordinates of the center is shown in figure 4.

We noticed that this “initial” transient is visible in all these measurements, like that done on July 1st (see figure 5).

During the daily meeting we decided to repeat the measurement with the N arm locked to avoid every movement of the input mirror. To try to keep the arm locked, the RH has been switched on with 7.5 W. A new DET-HWS acquisition was started and at 15.11 UTC NI RH was switched on.

After 1 hour and 39 minutes, Matlab crashed and the measurement stopped at WF 104, the RH curvature didn’t reach the steady state and at 17.06 UTC it was switched off. The north arm remained locked for the entire measurement. We checked the same signals seen before (figure 6).

The entire behavior of the coordinates of the center is shown in figure 7, where the green line is the RH switching on and the colored parts refer to the WFs observation and study, see the following table and the figure 8. Comparing figure 7 and figure 5, we can see that, given the lower power applied to the RH, the coordinates of the center of the RH curvature is noisier.

NI RH 20220712T1700

rowc [pixel]

colc [pixel]

Y coord [mm]

X coord [mm]

WF 26-41 (blue part)

206+-48

366+-46

-48+-8

-23+-7

WF 42-46 (red part)

277+-60

462+-59

-37+-9

-8+-9

WF 47-60 (yellow part)

337+-34

531+-24

-27+-5

3+-4

WF 61-104 (violet part)

433+-38

526+-42

-12+-6

2+-6

The displacement of the center coordinates is still visible. Nevertheless, we could proceed with the centering of the HWS beam on the NI center using the same ITF configuration.

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