Design and three-dimensional magnet mapping and calculation for the HERA correction dipoles

In order to correct the beam in the electron ring of the Hadron Electron Ring Accelerator double storage ring, two types of correction dipoles are required which have the same yoke and air-cooled coils, and differ in their pole plates only. By changing the pole plates, the pole distance can be easily varied. The magnetic fields of the two magnet types are measured and compared with 3-D field calculations made with the computer code PROFI. The results in the air gap are practically identical, while the calculated field is generally about 5% too high at the edge of the pole and approximately 1-2% too high towards its margins.