An achromatic quadrupole lens doublet for positive ions

The resolution and chromatic aberration of a doublet of achromatic quadrupole lenses have been experimentally measured. Each achromatic lens is of length 5.99 cm and comprises an electric quadrupole of bore 1.05 mm and a magnetic quadrupole of bore 3.40 mm. In preliminary tests with 600-keV protons, a chromatic aberration coefficient of less than 1.2 cm and beam width of 4 μ are measured, compared to 20 cm and 4 μ for the same doublet operated in a solely magnetic mode.