Beam Bump Method of Target Engagement

At the Cambridge Electron Accelerator we have developed a technique of engaging a thin tungsten target, located in a field-free straight section, with a 6 Gev electron beam. A distortion (bump) of the equilibrium orbit of the synchrotron is produced by powering backleg windings on four selected synchrotron magnets in a prescribed way. This method is equally useful for engaging a radially-inside or radially-outside target. Smooth spills of the electron beam on the target have been achieved for periods of 100 to 3000 micro-seconds at energies of 0.5 to 6.0 Gev. The backleg windings are powered by pulse-forming networks which can be operated asynchronously (e.g. 59 out of 60 pps.) Three such systems exist at the laboratory enabling up to three experimenters to perform experiments at the same time. Each experimenter receives an allotted number of pulses out of the 60 machine pulses which are available each second.