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A new 3-axis magnetic field measurement system based on the Hall elements has been constructed at KEK. The new system was designed for the larger magnets of higher energy accelerator facilities such as J-PARC. We employed a 7 m long 2 m wide iron base, and the magnet and the field mapping machine were set on the same base. We set pivot fittings at intervals of 250 mm through the longer side of the base. Therefore the alignment accuracy between the mapping machine and the magnet is promised within 0.1 mm in total by simply putting the magnet on the base. In addition, by teaching the mapping-machine coordinates of the two separate points on the magnet axis to the mapping machine, the field measurement points on the magnet coordinates can automatically be calculated and positioned in software way. We used three single-axis Hall elements mass-produced by industry. 3 Hall elements could be mounted on a rectangular PEEK block. The distance between hall elements is approximately 3.3 mm. The accuracy of 3 directions of Hall elements is within 0.5 degrees. The temperature of Hall elements was controlled within 60 ±0.1 degrees centigrade. Owing to the light weight of the Hall sensor unit and the strong carbon fiber rod with one side support, the bend of the rod was less than 10 mm for 2200 mm rod length. Thus we have successfully measured the field of the big Q-magnet, whose bore diameter and length are 200 mm and 3 m.
Date of Publication: June 2004