Axial ion focusing in a miniature linear ion trap.

A novel miniature linear ion trap with a total length of 19 mm and a quadrupole rod length of 15 mm has been fabricated to enable ion focusing in the axial plane (between the end caps). Each end cap includes an inwardly projecting tubular section, which prevents dc fringe fields from penetrating to the center of the miniature linear ion trap and aids in ion extraction. Axial focusing of ion packets to dimensions of less than 1 mm through collisional cooling is predicted and demonstrated in the miniature linear ion trap. Due to this demonstrated collisional cooling, narrow kinetic energy distributions are also illustrated on batch ion extraction as might be useful for ion transfer to enable subsequent mass analysis.