Real time dispersion measurements at the MIT Bates linac

The MIT-Bates Linear Accelerator Center comprises a 1 GeV electron linac/recirculator system, beam lines to two main experimental halls, and a pulse stretcher/storage ring. Proper tuning of the beam requires the transverse dispersion to be zero, or some specified non-zero value, at all locations along the beam lines. Dispersion measurements are made by correlating beam positions measured by BPMs, with energy measurements made using a BPM in a region of known non-zero dispersion. Data are acquired continuously from the BPMs and displayed on a graphical user interface in real time. This allows the accelerator operators to set dispersion quadrupoles and sextupoles so that the first and second order position and angle dispersions have their correct values at all points along the beam line. Details of the system design and operation are presented.