The T2-MK2 target at Position 4 has been adjust to approximately +1.5mm offset. This causes the ladder to be moved downwards, raising the beam spot location on the target window. The potentiometer ratio at this offset is approximately 0.810 (> 0.8059 nominal ratio for position 4, and therefore closer to Position 5)
The purpose of the offset is to better center the beamspot on the target window. Target window photographs showed the beam spot being slightly below center (See E-Log #197), and target ladder elevations taken in Spring 2016 showed the Position 4 target approximately 1.0mm above the profile monitor center.
MCR has been instructed to continue running with this offset, and a message with details on how to do so was posted to their Plone site. |