Monitoring system to permit accurate alignment of beams at collision in CESR

Colliding beams in a storage ring should be aligned, in position and angle, to within a small fraction of the beam dimensions. The problem lies in the measurement of the alignment error. Errors may be corrected by the use of appropriate steering elements. In the system used at the Cornell Electron Storage Ring (CESR), the orbits of e/sup +/ and e/sup -/ are measured simultaneously, to reduce the effect of small orbit fluctuations with time. In addition, the signals are processed in an automatic gain control (AGC) system which extracts the e/sup -//e/sup +/ pulse height ratio, with the e/sup +/ pulses being brought to a fixed level. When the beams are coincident, the e/sup -//e/sup +/ pulse height ratios will be identical on all four buttons of the beam position monitor. The AGC technique reduces the errors produced if the orbit is not well centered between the pickup buttons.<>