Virgo Logbook

Starting at GPS 1150615700 and for 17 mn we moved the M18_tx and M18_ty by batch of 100 steps in order to deduce the beam size at the Pstab box quadrant level (SIB1) (details in the 34111 logentry).

# Summary:
M18_tx leads to 0,0017 V @ QD1_DC_h per step
M18_tx leads to 0,0029 V @ QD2_DC_h per step
M18_ty leads to 0,0011 V @ QD1_DC_v per step
M18_ty leads to 0,0017 V @ QD2_DC_v per step
(see logentry in comment for details)

# Data of the optical configuration:

M18 picomotor calibration: 30 nm/step
M18 mount arm lever = 6,032e-2 m
-> M18 induces a beam tilt : 9,9e-7 rad/step

Dist(M18-Lens) = 0.225 m
Dist(Lens-QD1) = 0.160 m
Dist(Lens-QD2) = 0.410 m
Focal length = 0,400 m

(ABCD) matrix from M18 to QD1 = [0,6 0,295; -2,5 0,4375]
(ABCD) matrix from M18 to QD2 = [-0,025 0,4044; -2,5 0,4375]

M18 to QD1 conversion: 9,9e-7*0,295 = 2,9e-7 m/step
M18 to QD2 conversion: 9,9e-7*0,404 = 4,0e-7 m/step

PSTAB_QD1_DC = 1,415 V
PSTAB_QD2_DC = 1,445 V

From M18tx:
--> @ QD1 quadrant: S_QD1 = 5862 V/m and 4143/m (normalized with QD1_DC)
--> @ QD2 quadrant: S_QD2 = 7250 V/m and 5017/m (normalized with QD2_DC)

From M18ty:
--> @ QD1 quadrant: S_QD1 = 3793 V/m and 2680/m (normalized with QD1_DC)
--> @ QD2 quadrant: S_QD2 = 4250 V/m and 2941/m (normalized with QD2_DC)

we have assumed the alignment error signal to be S = 2*sqrt(2/pi)*Shift/w*P,
with
P: overall power on the quadrant in Volt
w: beam radius on the quadrant in m
shift: beam offset on the quadrant in m

we deduce the beam radius at quadrants to be:
from tx
w_QD1 = 385 um
w_QD2 = 318 um

from ty
w_QD1 = 595 um
w_QD2 = 542 um

Difference may be due to the uncertainty on the picomotors calibration