Design of a compact focusing lens system with short acceleration tube at 300Â kV

A compact focusing lens system with high demagnification over 1500 was designed to form an ion nanobeam with 346 keV energy by adding a short distance acceleration tube for beam acceleration and focusing downstream of the existing double acceleration lens system. The demagnification, focusing points and aberrations of the acceleration tube were studied using beam trajectory calculation. The acceleration tube was designed to have a length of 140 mm and a demagnification of 2 at its acceleration tube voltage of 300 kV, which resulted in a new compact focusing lens system with a total length of about 640 mm. In addition, the maximum voltage and electric-field of the acceleration tube were confirmed experimentally on the built device to be 300 kV and 30 kV/cm, respectively. The final beam size formed by the system was estimated to be 130 nm in diameter using the design parameters. The result suggests that an ion nanobeam of 346 keV can be formed by an apparatus having the reasonable length of 2 m, which permits us to develop a system for 1 MV by elongating its tube length.