Plasma thruster (2, 120) comprising a discharge chamber comprising an internal cavity and an outlet opening; at least one injection means (10, 12) comprising an injection nozzle capable of injecting into the discharge chamber a propellant gas along a predefined axis (A-A); said injection nozzle having an outlet end; a magnetic field generator (50, 52, 54, 58) capable of setting electrons of the propellant gas present in the discharge chamber in gyromagnetic rotation; and an electromagnetic wave generator capable of irradiating the propellant gas present in the discharge chamber by generating at least one electromagnetic wave the electric field of which has a right-hand circular polarization and a frequency equal to the frequency, F ECR, of gyromagnetic resonance of the electrons of the propellant gas magnetized by said magnetic field generator (50, 52, 54, 58), - said magnetic field generator (50, 52, 54, 58) is capable: ∘ on the one hand, of generating a magnetic field having field lines which determine an iso-field surface, known as the "ECR surface", with an intensity equal to that allowing a cyclotron resonance of the electrons under the effect of said electromagnetic wave; ∘ on the other hand, of giving said field lines the shape of a nozzle, so as to generate a diamagnetic propulsion force; - said injection means being produced from an electrically conductive material and being electrically connected to the electromagnetic wave generator so as to also operate as an electromagnetic antenna emitting said electromagnetic wave into the propellant gas at the outlet of said injection nozzle; wherein said magnetic field generator (50, 52, 54, 58) is capable of generating a magnetic field ■ producing an ECR surface enveloping the outlet end of said injection nozzle, the volume delimited by this ECR surface being the resonant cavity of the electromagnetic wave; ■ having a first local maximum of intensity inside the injection nozzle and at the outlet end of the injection nozzle; ■ having a second local maximum of the intensity of the magnetic field inside the injection nozzle, separated from the first local maximum by a local minimum of the intensity of the magnetic field inside said injection nozzle; - said injection means: ■ is produced from a magnetically conductive material, making it possible to achieve, inside the latter, said second local maximum of the intensity of the magnetic field; ■ comprises, at the downstream end of said injection nozzle, an injection channel with an external diameter strictly comprised between 0.5 and 3 mm. - said magnetic field generator (50, 52, 54, 58) is capable: ∘ on the one hand, of generating a magnetic field having field lines which determine an iso-field surface, known as the "ECR surface", with an intensity equal to that allowing a cyclotron resonance of the electrons under the effect of said electromagnetic wave; ∘ on the other hand, of giving said field lines the shape of a nozzle, so as to generate a diamagnetic propulsion force; ∘ on the one hand, of generating a magnetic field having field lines which determine an iso-field surface, known as the "ECR surface", with an intensity equal to that allowing a cyclotron resonance of the electrons under the effect of said electromagnetic wave; ∘ on the other hand, of giving said field lines the shape of a nozzle, so as to generate a diamagnetic propulsion force; - said injection means being produced from an electrically conductive material and being electrically connected to the electromagnetic wave generator so as to also operate as an electromagnetic antenna emitting said electromagnetic wave into the propellant gas at the outlet of said injection nozzle; wherein said magnetic field generator (50, 52, 54, 58) is capable of generating a magnetic field ■ producing an ECR surface enveloping the outlet end of said injection nozzle, the volume delimited by this ECR surface being the resonant cavity of the electromagnetic wave; ■ having a first local maximum of intensity inside the injection nozzle and at the outlet end of the injection nozzle; ■ having a second local maximum of the intensity of the magnetic field inside the injection nozzle, separated from the first local maximum by a local minimum of the intensity of the magnetic field inside said injection nozzle; ■ producing an ECR surface enveloping the outlet end of said injection nozzle, the volume delimited by this ECR surface being the resonant cavity of the electromagnetic wave; ■ having a first local maximum of intensity inside the injection nozzle and at the outlet end of the injection nozzle; ■ having a second local maximum of the intensity of the magnetic field inside the injection nozzle, separated from the first local maximum by a local minimum of the intensity of the magnetic field inside said injection nozzle; - said injection means: ■ is produced from a magnetically conductive material, making it possible to achieve, inside the latter, said second local maximum of the intensity of the magnetic field; ■ comprises, at the downstream end of said injection nozzle, an injection channel with an external diameter strictly comprised between 0.5 and 3 mm. ■ is produced from a magnetically conductive material, making it possible to achieve, inside the latter, said second local maximum of the intensity of the magnetic field; ■ comprises, at the downstream end of said injection nozzle, an injection channel with an external diameter strictly comprised between 0.5 and 3 mm.