Partly sealed ion guide and ion beam deposition system

Disclosed herein is an ion guide for guiding an ion beam along an ion path, said ion guide having a longitudinal axis which corresponds to said ion path. Said ion guide comprises a plurality of electrode plates which are arranged perpendicularly to the longitudinal axis, each electrode plate having an opening and being arranged such that said longitudinal axis extends through its respective opening, wherein said openings collectively define an ion guide volume. The ion guide extends or is configured to extend through a separation wall separating adjacent first and second pumping chambers. The ion guide has a first portion, in which gaps are formed between at least some of said electrode plates such that uncharged gas can escape from said ion guide volume, wherein said first portion is completely located in said first pumping chamber. A second portion, in which sealing elements are arranged between adjacent electrode plates, prevents neutral gas from escaping from that portion of the ion guide volume between adjacent electrode plates, said second portion extends at least from said separation wall into said second pumping chamber.