Investigation on the radial distribution of electron density in a miniaturized ECR ion thruster of wide-range operations

A miniaturized thruster with a wide tuning range of thrust plays an important role for the drag-free control in the task of space-borne gravitational wave detection. For the design of a high-precision miniaturized thruster, it is necessary to study the spatial distribution of the electron density in its discharge chamber. This work investigates the electron density distribution in an ECR ion thruster of 2-cm diameter, with the input microwave power and mass flow rate tuned in a wide range. At relatively low power and flow rate, there is a peak of electron density at the radial position r = 4 mm, which is around the region of resonant power absorption. However, the density distribution in the center region becomes flat with the increase of power and flow rate; at high power and flow rate, it tends to be a Bessel function with a peak in the center (r = 0 mm). In the view of tuning of thrust, it is found that the above variation of electron density distribution can be as important as (or even more important than) the variation of peak value of electron density. A further discussion on the influence of the evolution of electron density distribution is given by considering the thruster design, operation, and control for the task of space-borne gravitational wave detection.