Magnetic field distribution and image field index for short axial length E layers

A study is made of the influence of different current density distributions on the magnetic field distributions and effective image field indices for axially short astron E layers or rings. Significant differences are found between the newly calculated values of the image index and those derived from long-layer models. For short axial lengths, which correspond to most observed electron rings, both the magnetic field distributions and the effective image indices do not depend strongly on the current distribution within the ring. Good agreement is found between the theoretical stability limits implied by the presented field indices and the ''dump'' levels observed in the RECE-Berta experiment