INJ recovery :
Power calibrations :
Having fixed the power fluctuations at the PMC output that were due to loop oscillation. We worked on the calibration of the photodiodes and power budget :
With 0.615 V on PMC TRA we measured 51 W at PMC output.
With 29.6 W measured after M5 we had 30.4 W on EIB_PD_out not.
With IPC1 at full power we had 41.4 W out of the 51 W at PMC output.
This means 1-(41.4/(51*0.97)) about 16.4 % losses in the EOM FI IPC line.
The losses are quite high but the beam does not seem to be clipped. A potential explanation could be the angle of incidence of the beam arriving on the TFP polarizers at the input and output of the faraday. They are quite sensitive to the aoi.
We tried to tune the HWP of the FI but it was already set to the maximum. Rotated them is not straight forward, we did not ush this investigation any further.
With 29.4 W measured after M5, we worked on the alignment and managed to get 18 W on IMC TRA. The power seen by the IMC TRA photodiode was consistent with the ones seen by the PSTAB photodiodes.
So it seems that we have an overall throughput of the IMC of the order of 18/29.4 = 0.61% which seems similar to what we had last time we measured the throughput losses (#67826)
By looking at the power on IMC REFL in locked and unlocked states and getting rid of the offset we have : (1.12−0.35)÷(6.38−0.35) = 12.8 % of the power which is reflected when we are locked with 18 W on IMC TRA.
Detailed study to make the comparision with previous power budget studies to come.
To be noted that somehow the DC values seen by the different PD and QPD have changed. This is a phenomena that has already been seen in the past and that could not be explained if not by the polarization somehow slightly rotating wile aligning on the parabolic mirrors and the IPC in front of the PD working closed to the full exctinction (#45306). We will investigate it and we will report the DC values to their normal working point.
Issues to be solved : BPC DSP non responding
Still to be done when the EIB will be suspended: close the IMC AA, potentially need to redo the matrix. General check of the loops. Updated throughput budget
BPL :
We measured the beam properties and they are has expected for both NF and FF about 400 um with accumulated gouy phase difference of 90 degrees (see plots).
We power supplied the QPD and checked their behavior. For now they look quite noisy, especially the FF (see attached figure) but we should close the enclosure of EIB and suspend it before making any conclusion.
We could also see some resonance at 1.7 kHz with harmonics at 50 Hz that could be linked to one of the PZT.
Still to be done : Connect the PZT to the DAC and check their good functionning. Commissioning of the loop with EIB suspended.
