High-Quality Narrow Quadrupole Magnets

Two sizes of narrow quadrupole magnets (8 and 12 in. diam) have been designed and built at Berkeley for use in Bevatron experiments. The quadrupole magnets have a small width for the given aperture, so two or more secondary beams can look at the same target at small production angles. The computer program RNIL was used to develop the pole-tip contour, and the resulting design produced a quadrupole with very small harmonic content. Measurements of the line integral for the 8-in. quadrupole at a gradient of 2800 G/in., measured at a radius of 3.67 in., give harmonic contents, expressed as per cent of second harmonic, of 0.1% for the sixth, ≤0.03% for the tenth, and 0.05% for the fourteenth.