Design, fabrication and calibration of a cryogenic search-coil array for harmonic analysis of quadrupole magnets

A cryogenic search-coil array was fabricated for harmonic error analysis of Superconducting Super Collider model quadrupoles. The coil consists of three triplet of coils: the center-coil triplet is 10-cm long, and the end coil triplets are 70-cm long. Design objectives are a high bucking ratio for the dipole and quadrupole signals and utility at cryogenic operating currents (-6 kA) with sufficient sensitivity for use at room-temperature currents ( approximately 10 A). Individual coils were measured mechanically to +or-5 mu m, and their magnetic areas measured to 0.05%. A computer program was developed to predict the quadrupole and dipole bucking ratios from the mechanical and magnetic measurements. The calibration procedure and accuracy of the array are specified. Results of measurements of SSC model quadrupoles are also presented.