A Hall effect plasma accelerator comprises an annular accelerating channel having closed and open ends. A source of magnetic field is positioned behind the closed end of the channel and has an axis extending in the same direction as the axis of the channel. This makes it possible to provide a Hall effect accelerator with an optimum distribution of magnetic field inside the acceleration channel by means of a simpler and less heavy arrangement using a single source of magnetic field, such as a single coil or permanent magnet. In addition it makes possible a reduction in heating of the source of magnetic field.