Passive focusing of proton and ion beams using a stack of thin conducting foils have been predicted in a recent paper[1] based on a statistical transverse envelope model for a monoenergetic single-species ion beam propagating through infinitely thin conducting foils.The foils effectively screen the beam defocusing self-electric field while preserving the beam focusing self-magnetic field,enabling a strong net focusing to a small transverse spot whose size is comparable to the foil spacing size.This passive focusing scheme has also been experimentally investigated with promising first observations[2].