Small-caliber and variable-aperture grid assembly

The invention discloses a small-caliber and variable-aperture grid assembly. The target of prolonging the service life of an ion thruster is achieved by improving the beam extraction uniformity and prolonging the service life of the grid assembly. An accelerating grid in the grid assembly is uniform in diameter; an opening region of a screen grid is divided into a plurality of regions with different pore diameters; the pore diameters are sequentially increased progressively from small to large from the center region to the edge region, so that the beam extraction in the center region is suppressed and reduced; and the beam in the edge region is increased to improve the beam uniformity. Due to the reduction of the beam in the center region, charge exchange ions in the region can be effectively reduced, so that sputtering corrosion to the region of the grid assembly caused by the charge exchange ions is reduced, and the service life of the grid assembly is prolonged.