MULTI-TESLA PERMANENT-MAGNET FIELD SOURCES

Both cylindrical (''magic ring'') and spherical (''magic sphere'') dipolar Permanent magnet field sources are capable of providing arbitrarily high fields in their interior cavities. However, since the obtainable field increases only logarithmically with the structural radius, fields above about 2.5 T necessitate excessively massive and costly structures if working volumes of more than a few cm3 are desired. The present work shows how for some cavity shapes the structures can be modified to produce fields up to 4.0 T with only about one fifth the mass and bulk of the conventional structures. Possible applications which would be impractical with the unmodified field sources are cited.