Correcting Closed-Orbit Distortion in the NAL Main Ring

The position of the equilibrium orbit in the NAL synchrotron is measured by sensors immediately downstream of ring quadrupoles. The orbit distortion is corrected at low magnetic field by dc correction magnets located adjacent to the sensors and at high field by transverse displacements of the ring quadrupoles. The inconvenience of moving quadrupole magnets has favored making the minimum number of moves necessary to obtain adequate reduction of the maximum orbit distortion. A few familiar mathematical techniques have proved adequate to calculate the correcting moves, but the combination of these techniques is data dependent. A computer search program invariably gives a solution, but it has been useful to experiment with weighting and smoothing of the data and to compare alternative calculations to insure that the solution is optimum with respect to our priorities and constraints.