Grid shadow pattern analysis of achromatic quadrupole lenses

Abstract

An achromatic triplet of quadrupole lenses has been designed as a probe forming lens system for a 2.55 MeV H+ beam. The parasitic aberrations of the three magnetic and three electrostatic lens components have been measured with the grid shadow method. The lenses were found to have up to 1.3% parasitic sextupole components and up to 3.4% parasitic octupole components, as well as some skew multipole components assumed to be similar in magnitude to the former components. The electrostatic lenses, constructed with a novel design, had parasitic components comparable in magnitude to the magnetic lenses which were constructed with a conventional design. In achromatic mode, the most significant para..