The aim of our shift was to mitigate the scattered light on the External Injection Bench.
We started by realigning the beam into the Faraday Isolator by turning the vertical screw of EIB M3 (clockwise). The beam seemed better centered into the IPC1 (it used to be too high). We then had to manually realign the beam in order to close the BPC loop. The shape of the IMC reflection (plot 1 and 2) slightly changed, so that we had to remeasure the automatic alignment sensing matrix.
We also installed some beam dumps: in transmission of EIB_M2, EIB_M4, on EIB BP1 and aside from it. Boris Boom from remote rebalanced the bench.
The final trial we did is to rotate by 90 the waveplate of the IPC1. Supposing that the beam is not perfectly centered on it in fact, there could be an impurity which scatters light and by turning it we should see an improvement. We restored the nominal power 19.4 W (a trend of the INJ powers is shown on plot 3).
************* new Aa sensing matrix
PR_SUM_CH MC_ty 17.89 MCT_hNORM 0.00 FF_ACh -0.09 NF_ACh
PR_SUM_CH IB_ty 29.26 MCT_hNORM 0.00 FF_ACh -0.80 NF_ACh
PR_SUM_CH MC_tx 6.24 MCT_vNORM 0.68 FF_ACv -0.23 NF_ACv
PR_SUM_CH IB_tx 34.68 MCT_vNORM 0.75 FF_ACv -0.25 NF_ACv
PR_SUM_CH IB_tz 5.98 MCT_vNORM 0.31 FF_ACv 1.07 NF_ACv
MC ty gps = 1254494746.00
IB ty gps = 1254493668.00
MC tx gps = 1254494591.00
IB tx gps = 1254493458.00
IB tz gps = 1254493764.00