Prevention of halo formation in high brightness beams

A four vane quadrupole structure with a duodecapole field component is analyzed to suppress emittance growth and halo formation in high brightness beams. The beam profile in such a structure has to be close to square instead of conventional circle cross section. The adiabatic change of electrode shapes along the channel results in transformation of an initially nonuniform beam into the beam, matched with the channel with a pure quadrupole field. Results of prevention of halo formation in the bright beam with a phase space density of 1.5 A/(π cm mrad) are given