Electron beam position stabilization with a piezo-electric optical correction system

A piezo-electrically controlled optical correction system was successfully used to reduce the helicity-correlated pulse-to-pulse position differences of a laser spot to better than ±100 nm at a pulse rate of 600 Hz. Using a simple feedback algorithm, average position differences of Δx=−3.5±4.2 nm and Δy=2.6±6.6 nm were obtained over a 6 h period. This optical correction system was successfully used in the polarized electron source at the Bates Linear Accelerator Center to stabilize the position of the electron beam during the recent SAMPLE experiment. Because this experiment measures a parity violating signal at the 10−6 level, it is sensitive to systematic effects which are correlated with the helicity of the incident electrons. One potentially large systematic effect is the helicity-correlated motion of the incident electron beam. By using this optical correction system, electron beam position differences at the location of the experiment were routinely kept well below ±100 nm, with averages over the entire two month run of Δx=6.4±2.3 nm and Δy=−3.5±2.0 nm.