After the work done by Bulten and co on the EIB rebalancing with started to work on the realignement of the beam from PMC output towards the BPC quadrant with the EIB blocked in its nominal position.
To do so we locked the PMC with the reflection as a trigger. The LB_M13 is still a beam sampler that reflect only about 1% of the PMC TRA. The power was also reduce at the PMC input by about 50%. As a result we were working with a beam of about 350 mW to do the alignment.
We started by aligning the beam into the apertures which are at the output of the LB, using LB M13 and LB M14. While arriving on the EIB, we noticed that the beam was relatively low, few mm below the usual working point (100 mm). This is not completly explained, we checked the apertures at the output of the LB that were effectively at 100 mm. This discrepency can either be due to a height difference between the two benches or it means that we are not well aligned in the lens (f = 1000) at the output of the laser bench. The heght of this last an not be set.
We decided to keep the pinholes as the horizontal reference for the beam at the output of the LB but to use M13 and M14 to get a beam propagating in the 100 mm plan on EIB. We did so and adjusted the height of the apertures at the output of LB.
From here we started the alignement of the beam on EB by setting the miror EIB M1a M1b and M1c. We used M1a and M1b to ensure that the beam was propagating in the 100 mm plan and in the right direction for the transmission of M1c that will be used both for ALS and for the BPL loop. Once it was done we moved M1c by hand both in horizontal shift and horizontal tilt to pass through the EOM and eventually reached the photodiodes downstream ( BPC QN DC and QF DC for example). We managed to get the expected DC on both quadrants about: 0.006 V for 0.35 W of PMC TRA while we usualy have about 1V for 60 W of PMC TRA.
From here we started to work on the alignment of the optics downstream of M1c.
We noticed that we were very high on PT_M1, also the Y of the BPC was quite out of range.
This is explained by the fact that the algnment on EIB as alwas been done with a beam that was slightly lower.
We decided to go on with a general realignment on EIB. At first we got the beam back in the 100 mm plan in transmission of M1c, using M1a and M1b, and check that we were indeed correctly passing through the EOM.
Then we used EIB M3 to get the beam centered at the exit of IPC1/ M4. Then we used the mirrors one after the other till M8 to center the beam on each other.
We eventually got some signals on both NF and FF QPD (note for the future : IBJM is convenient to visually check the FF).
We will go on with the final fine alignment on monday.