Experimental study of ion optics with square apertures for high-power ion thrusters

Large-diameter ion-optical systems are widely used in gridded ion thrusters for missions in near-earth space and for deep-space research. Ion sputtering of the accelerator grid is the main factor that limits the thruster's life. The use of carbon-based materials with a lower sputtering rate compared to metal grids allows the thruster to increase its life more than four times. The most resistant to mechanical loads are grids made of carbon-carbon composite materials. Traditionally, ion optics grids use circular-shaped apertures with the centers located in the nodes of the hexagonal pattern. However, with this arrangement of holes, all carbon fibers in the carbon-carbon composite are cut, and this weakens the mechanical strength of the grid. Previously, the Keldysh Research Centre carried out computational studies of a new form of apertures, in which it is possible to preserve uncut fibers and thereby increase the mechanical strength of grids made of carbon-carbon composites. This paper presents the results of a comparative experimental study of the operational characteristics of ion optics with the traditional round shape of apertures and with the new shape of apertures, which are squares with rounded corners. Measurements of the accelerator grid currents depending on the accelerating voltage have shown that both traditional and new ion-optical systems have close perveance limits in which there is no direct ion impingement on the accelerator grid.