LENTE MAGNETICA A MAGNETI PERMANENTI DI TIPO IBRIDO CON DISPOSITIVO DI REGOLAZIONE DEL GRADIENTE DEL CAMPO MAGNETICO

There is described a magnetic lens having a structure of essentially cylindrical shape, comprising pole pieces 21 of ferromagnetic material and flux generators 22 of permanent magnet type, interposed between adjacent pole pieces 21. The pole pieces and the flux generators define a plurality of magnetic fields of alternating sign which delimit between themselves a multipolar field region which extends symmetrically along the axis of the cylinder. To optimise the structure from the standpoint of flux scattering, each of the flux generators 22 projects radially outward, relative to the external lateral walls of the pole pieces 21, by a predetermined amount s calculated so as to minimise the scattering of the magnetic field flux. Furthermore, to allow for the balancing of the lens and its adaptation to a specific application, at least one of the pole pieces 21 has at least one part 21B which can move relative to the rest of the structure to vary the magnetic field gradient of the lens.