Transient Behavior of Ion Extraction and Acceleration of Variable Thrust Ion Thruster

Abstract

Numerical simulations were carried out to understand the transient behavior in ion extraction and acceleration for a variable-thrust ion thruster, thrust in which is controlled by changing the duty ratio of the ion extraction-on and extraction-off periods. The duty ratio is controlled by rapidly switching the accel grid voltage with a rising and falling time of several hundreds of nanoseconds. Calculation results showed that the thrust could be varied by the on/off control of ion extraction; however, the transient direct impingement of ions caused grid erosion. Thus, the effect of grid erosion on lifetime was evaluated for the planned on/off cycles, which showed that grid erosion was negligible compared to that by charge exchange erosion. In addition, the parametric analysis of the rising and falling times showed that the grid erosion is a function of the rising and falling time and it reaches a minimum at a rising and falling time of around 200 ns.