J Mater Sci Technol ›› 2004, Vol. 20 ›› Issue (01): 125-128.

• Research Articles • Previous Articles    

Magnetic Field Design by Using Image Effect from Iron Shield

Quanling PENG, S.M.McMurry, J.M.D.Coey   

  1. Institute of High Energy Physics (IHEP), Chinese Academy of Sciences, P.O. Box 918-9, Beijing 100039, China
  • Received:1900-01-01 Revised:1900-01-01 Online:2004-01-28 Published:2009-10-10
  • Contact: Quanling PENG

Abstract: Permanent magnet rings are presented, which exploit the image effect in the surrounding circular iron shields. The theory is given for a general permanent ring when the magnetization orientation φ at each coordinate angle ψ changes by φ=(n+1)ψ, where n is a positive or negative integer. For the uniformly magnetized case n=-1, the permanent ring produces no field in its bore, and the field is that of a dipole outside. When the ring is surrounded by a soft iron shield, its field becomes uniform in the bore, and zero outside the ring. The field can be varied continuously by moving the iron shield along the magnet axis. A small variable field device was constructed by using NdFeB permanent rings, which produced a field flux density of 0~0.5 T in the central region.

Key words: External magnetic field, Internal magnetic field, Cylindrical iron shield