An automatic beam focusing system for MeV protons

An automatic focusing system for MeV protons has been developed. The focusing system utilises rapid real time proton induced secondary electron imaging of a calibration grid coupled with a modified Gaussian fit in order to take into account the enhanced secondary electron signal from the calibration grid edge. The focusing system has been successfully applied to MeV protons focused using a coupled triplet configuration of magnetic quadrupole lenses (Oxford triplet). Automatic beam focusing of a coarse beamspot of approximately (5 × 3.5) micrometres in the X and Y directions to a sub-micrometre beamspot of approximately (0.7 × 0.6) micrometers was achieved at a beam current of about 50 pA.