FLlamas - Tuesday, 2025-02-25
Start of report
Moved the Pcal upper beam at END-X to test for repeatability of the results seen on LHO:78373.
Recap:
As seen on first figure (chi_klm), the red squares highlight the inconsistency when moving the upper and the lower beam to the same direction (left aperture on target - fourth and fifth figures show the target) on the ETM. The other moves are consistent between upper and lower beam. Additionally, the second (2024_06_11_transition_upper_center2left_rawpcals_out) and third (2024_06_18_transition_upper_left2center_rawpcals_out) figure show the Pcal channels during the upper beam moving from the target center aperture to the left aperture and back. The blue color is for the PD values before making an actuation, the orange is for the values after the actuation, the title tells the actuation direction on the target and the x-axis is the time needed to average 10 hours within lock for each state (10 hrs before and 10 hrs after). From these plots we see that, during the upper-beam actuation to the left and back, the END-X Tx sensor - middle-left plot - decreased by 8 HOPs and 6 HOPs, affecting chi_XY. The END-X Rx value - top-left plot - dropping by 20 HOPs suggests additional losses of the beam downstream from the Tx sensor, potentially from clipping, but it is hard to see with the Tx changing simultaneously. There was an initial concern at the time of moving the upper beam that the actuations to the right aperture were the inconsistent ones, but after moving the lower beam we can have more confidence on the values corresponding to an actuation to the right aperture and raise concern on the actuations done to the left aperture.
Today:
Went to END-X to move the upper Pcal beam by actuating on yaw of the last folding mirror before the vacuum window (aka: the "inner beam" folding mirror.) The objective is to maximize the signal measured by the Rx PD when the target is in place. This is done by blocking the beam that will not be used and monitor the actuated beam with a voltmeter reading from "RX PD Mon" from the Pcal interface chassis (D1400153). The table below documents each relevant step from the procedure and the voltage used to assess such step.
| Step | Comment | Keithley Voltage [V] |
|---|---|---|
| 1 | Both beams | 3.387 ± 2e-3 |
| 2 | Block outer (lower) beam | 1.682 ± 1e-3 |
| 3 | Target on (fourth figure | 1.412 ± 5e-3 |
| 4 | After actuation (fifth figure | 1.570 ± 2e-3 |
| 5 | Target off | 1.683 ± 1e-3 |
| 6 | Unblock outer beam | 3.389 ± 2e-3 |
The increase in signal after the actuation could be from clipping on the center aperture. An extra step between 3 and 4 where the beam is "optimized" on the center aperture would reveal if there is such clipping. The previous alog from a Pcal upper-beam actuation to the left agrees that this location increases the Voltage signal from RX PD Mon but the data shows 20 Hops of clipping... odd.
Nominal plan is to get a few hours of lock to assess the results from this actuation, and return the beam to it's nominal "center" state on the following maintenance Tuesday.
End of report
