Harmonic content of PEP dipoles and some related effects and lessons

The harmonic content of magnets such as the standard PEP bend is (among other things) a function of excitation current, the way the current is set and even the magnetization history. For instance, harmonic strengths generally vary not only with the magnitude of the current but the direction and rate at which the current is approached and set. The field distribution resulting from different procedures can vary markedly depending on both the mechanical and magnetic design and the degree to which eddy current effects are emphasized. Variations among magnets of the same design result from variations in the iron (e.g. its chemistry, lamination fabrication and treatment procedures etc.) as well as overall magnet fabrication procedures (e.g. from unobtainable tolerances on important assembly steps). Because the field distribution may also depend on the previous history of a magnet, all PEP dipoles were subjected to what are called magnetization and standardization cycles before measurement - the latter depending on the former and intended to set the initial conditions of the magnet to a reproducible standard. The primary goal of the magnetic measurements was then to determine the dipole strength as a function of current for each magnet based on a pratical setting algorithm. The main constraints on the algorithm were reproducibility of the integrated field, speed, power and reduction of higher harmonics. Quadrupole and sextupole strengths were also measured on about one-half of the magnets at one current (I = 1250A/E = 17.43 GeV). This note presents the data and discusses it from the viewpoint of subsequent measurements with stored beams