The spot positions on the MC mirrors were adjusted by steering the MC mirrors, resulting in 1 mm off-centering on each optic.
One of the requirements in aligning the MC mirrors is the differential spot positions in MC1 and MC3.
It determines the beam angle after the beam exists from MC, and if it's bigger than 3 mm then the beam will be possibly clipped by the Faraday (#4674).
The measured differential spot positions on MC1 and MC3 are : PIT = 0.17 mm and YAW = 1.9 mm, so they are fine.
(Measurement and Results)
Suresh and I aligned the MC cavity's eigen axis by using MCASS and steering the MC mirrors.
Most of the alignment was done manually by changing the DC biases
because we failed to invert the output matrix and hence unable to activate the MCASS servo (#5167).
Then I ran Valera's script to measure the amount of the off-centering (#4355), but it gave me many error messages associated with EPICS.
So a new script newsensedecenter.csh, which is based on tdsavg instead of ezcaread, was made to avoid these error messages.
The resultant plot is attached. The y-axis is calibrated into the amount of the off-centering in mm.
In the plot each curve experiences one bump, which is due to the intentional coil imbalance to calibrate the data from cnts to mm (#4355).
The dashed lines are the estimated amount of off-centering.
For the definition of the signs, I followed Koji's coordinate (#2864) where the UL OSEM is always in minus side.
After the beam spots on MC1 and MC3 were close to the actuation nodes (<1mm away)