Design of an E*B filter with improved velocity-separating capability

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Abstract
An E*B separator is described in which effective use is made of the fringing fields of the magnet. In the particular case described, this results in an increase of the velocity-separating capability of 40% with respect to the Wien filter that would have resulted if the fringing fields were completely shielded. It is also shown that for the normal operating conditions, the filter with fringing fields behaves as an ideal Wien filter without fringing fields but with drift spaces at the entrance and the exit. The effective length of these drift spaces and the length of the equivalent ideal Wien filter are slowly varying functions of a single parameter, the reduced magnetic induction, which depends on the operating conditions of the filter. A numerical example using a 12 in laboratory magnet is given.