RickS, FranciscoL

On Tuesday, May 14, we moved the pcal inner beam by 5 mm on the Rx sensor at X-End. This is the start of an investigation on potential sources of systematic variations to the pcal system.

Our procedure and notes are the following:

1. Connected voltmeter to 'Rx Mon PD' of pcal interface chassis (D1400153) front panel to monitor the signal from Rx when moving the beam.
   • Forgot to write down a value for Rx voltage, ndscope shows a value of 0.5165 W for 'H1:CAL-PCALX_RX_PD_WATTS_OUTMON' before making any changes (PCALX_RX_PD_WATTS_BEFORE).
2. Removed the Rx enclosure and closed shutter.
3. Placed and aligned target on integrating sphere input port (RxX_TargetAlignment). Opened shutter once the target was aligned.
   • Rx voltage of 2.87 V with both beams into the middle of the target.
   • Rx voltage of 1.49 V after blocking the outer beam.
4. Moved beam 5mm towards the right - facing the target (RxX_InnerBeamMoved), the left beam is the "centered", outer beam, the right beam is the "moved", inner beam.
   • This movement was done, instead of moving left, to avoid the out of vacuum coating edge. The equivalent of "moving to the right" at the target is adjusting counter clock-wise on yaw of the mirror mount. There was some adjustment to the pitch as well.
   • Rx voltage reached a peak at 1.447 V
5. Removed beam block to have both beams. Rx voltage of 2.844 V
6. Removed target.
   • Rx voltage was of 3.383 V
   • Ndscope shows a value of 0.5164 W after making changes (PCALX_RX_PD_WATTS_AFTER)

We expect this procedure to reflect the calculations done in T2400032 which depend on the position of the IFO beam and the pcal beams on the ETM. With this movement, and following the parameters from the technical note, we are expecting to see a change in the XY ratio of +19 HOPs (after - before). This procedure will be iterating in the following weeks, making a series of movements of the inner beam, with reports on the value obtained after making a beam movement.