ISR Sextupole Magnet

The 32 correction 6-pole magnets had the special feature of having an asymmetric aperture of 192 mm (horizontal) x 112 mm (vertical), the two central poles having been brought closer to the ISR elliptical vacuum chamber in order to save Ampere-turns and power. In fact for a given strength the required Ampere-turns per pole are proportional to the cube of its distance from the centre. The low-carbon steel core was 396 mm long , the strength 28 T/m. The strong dipole field generated at the ends by the asymmetry, as well as other unwanted multipoles, were compensated by suitable shaping of the pole profiles.