Electrostatic ion acceleration in an inductive radio-frequency plasma thruster

Spatially and temporally resolved ion flow measurements are performed inside the plasma source of an inductive radio frequency plasma thruster. Using the resulting data, the pure effects of the inductive current drive on the ion flow are identified. The cross field ion acceleration and the establishment of the cross field electric field are found in the upstream region, where the azimuthal current is induced by the superimposition of a time-varying magnetic field. Analyzing the electron and ion dynamics with two-fluid equations, the magnetized electrons form the in-plane Hall electric field to satisfy the electron force balance, which results in the electrostatic acceleration of unmagnetized ions. The enhanced density gradient forms a stronger Boltzmann electric field along the magnetic field. It generates a supersonic ion group along the magnetic field line, which increases the field-aligned ion flow velocity and the momentum thrust.