Results are described of an experimental study examining the laboratory model of the 5-cm xenon ion thruster with power in the range from 50 to 100 W. The investigation was aimed at the study of the efe ciency of the smallsize thruster discharge chamber operating in combination with two grid systems of different types at a low-power consumption. Abeam ion production cost between 260 ‐370 W/A at a propellant utilization efe ciency ranging from 0.77 to 0.81 was realized in experiments conducted with the laboratory model. The use of the string grid system with small elementary cell sizes and large transparency for ions is shown to reduce substantially the accelerator grid potential compared to the conventional e at grid system.