Further Improvement of Sector Instruments

To further improve the performance of a sector instrument in terms of scan speed, resolution, transmission, and mass range, the construction, in particular that of the magnet, needs some additional refining. 

Another problem is due to fringing fields. To reduce these defocusing effects at the entrance and exit of the field, the pole pieces of the yoke of the electromagnet generally have specially shaped edges (Fig. 4.20). 

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