A charged particle propagation apparatus has a generator including a vacuum chamber with a gun therein for discharging a charged particle beam through a beam exit. A higher pressure region adjoins the vacuum chamber at the beam exit and is maintainable at a pressure greater than a pressure of the vacuum chamber. A plasma interface located at the beam exit includes a plasma channel having at least three electrode plates disposed between its first end and its second end. A control system is adapted to apply a sequence of electrical currents to the electrode plates, which cause at least one plasma to move from the first end to the second end of the plasma channel, thereby pumping down the beam exit, and, in use, the charged particle beam is propagated from the vacuum chamber through the, or each, plasma into the higher pressure region.

A focused ion beam system has a differentially-pumped vacuum unit and a focused ion beam column, comprising: a vacuum pad, of a porous material, with a suction surface exposed in a way that surrounds the outer edge of a substrate to be processed; a substrate support on which the substrate and vacuum pad are placed, and a vacuum pump for vacuum evacuation using the vacuum pad. The system provides an arrangement in which, while a head of the differentially-pumped vacuum unit partially falls out of the outer edge of the substrate, the suction surface allows an input of air evacuated from a region between the suction surface and the head, and the processing area on a substrate is expanded by allowing the processing with an ion beam to be performed even in the vicinity of the peripheral substrate surface without requiring a large vacuum chamber.

A differential pumping apparatus for creating a high vacuum inside a processing space includes a displacement drive unit configured to move a substrate to be processed or a head, to adjust parallelism and distance between a surface to be processed and a surface of the head. Gap measurement devices are placed at three or more locations along the periphery of the surface of the head to provide distance information. A gap control unit is configured to control the displacement drive unit in response to the distance information between the surface to be processed and the surface adapted to face the surface to be processed, so that the surface to be processed and the surface adapted to face the surface to be processed are parallel.