The Plasma Ionization Mechanism for a Radio Frequency Ion Thruster with a Flat Coil Inductor

Abstract

A model of discharge for a radio frequency (RF) ion thruster with a flat induction coil is proposed. The configuration of magnetic fields and currents in 3D geometry is described. The skin layer boundary is determined by the condition at which the azimuthal current in plasma becomes zero under a transformer coupling with the inductor. Variation of radial magnetic field and azimuthal current at the generator driving frequency induces currents at the driving and second harmonic frequencies. Plasma becomes ionized due to magnetized collisional plasma electrons in mobile current layers. With operation at the optimal driving frequency, magnetic field of a definite sign fills the entire gas-discharge space in the course of convective diffusion within the current half-cycle. In the next half-cycle, it is filled with magnetic field of the opposite sign. Ohmic losses in the current layer are compensated in the course of field annihilation. The concentration of particles captured by the mobile layer was determined from the equality of “frosted” electron flows entering and leaving the layer in the course of single coulomb collisions with scattering at the pinch-angle. The azimuthal current of the fundamental harmonic component is determined by mobile layer currents outside the skin layer. The power losses are compensated by magnetic energy. The simulated results are compared with experimental data. The model of physical processes in radio frequency discharge with a flat induction coil has substantial peculiarities as compared with the discharge model using a cylindrical induction coil.