Patent ID: 7436122

Claim:
A thruster comprising: an electrical and magnetic acceleration stage having an endless, annular ion exit area, a magnetic structure for creating a generally radially directed magnetic field across the exit area and an electrical structure creating an electrical field generally perpendicular outward relative to the annular exit area, the magnetic structure including a midstem and a cylindrical outer core spaced outward of the midstem and defining an annular space therebetween, the midstem and outer core having corresponding front portions adjacent to the exit area and corresponding rear portions remote from the exit area, the magnetic structure further including a back plate magnetically coupling the midstem and outer cylindrical core at their rear portions; and a helicon plasma source for creating ions of propellant gas, the helicon plasma source being annular, having an inner cylinder and an outer cylinder spaced from the inner cylinder, an ion creation zone between the two cylinders, the ion creation zone being aligned with the annular exit area of the acceleration stage, the helicon plasma source having a magnetic circuit creating a generally axially directed magnetic field in the ion creation zone as compared to the generally radially directed magentic field across the exit area, the helicon plasma source being disposed within the annular space bounded by the midstem, outer core, and back plate of the magnetic structure.