More efficient RF plasma electric thruster

A high efficiency RF plasma thruster comprising:

• an RF generator for generating RF energy at a frequency f and a power P;
• a lower hybrid wave launching structure coupled to said RF generator, said wave launching structure comprised of plural radiating elements;
• a tube disposed within said wave launching structure, said tube defining an area within said wave launching structure and having a central axis of symmetry;
• a magnetic assembly disposed about said wave launching structure for establishing a magnetic field substantially parallel to said central axis of symmetry;
• a power supply coupled to said magnetic assembly for energizing said magnetic assembly;
• and
• a gas supply in fluid communication with and supplying gas at a rate r to said area defined by said tube, the gas within said area being excited by said RF energy emitted by said lower hybrid wave launching structure to provide a plasma including a lower hybrid wave which provides thrust having a specific impulse determined by the ratio of P to r,
• wherein each of plural said radiating elements is disposed in a respective plane substantially perpendicular to said central axis of symmetry,
• wherein said plural radiating elements are collectively disposed about said central axis of symmetry in a staggered array substantially parallel and along the lenght of said central axis of symmetry,
• wherein a time-varying electric signal is provided by said RF generator to each of said radiating elements, the time-varying electric signal provided to one of said plural radiating elements being out of phase with the time-varying electric signal provided to an adjacent one or ones of said plural radiating elements, and
• whereby said lower hybrid wave launching structure imposes a wavelength, determined by the phasing φ between adjacent ones of said plural radiating elements, substantially parallel to said magnetic field and said central axis of symmetry on waves in said plasma, said imposed wavelength satisfying the equation:
• ( d λ ) ⁢ ( 360 φ ) ≤ ω ce 2 ⁢ ω pe
• where
• d is the distance between adjacent ones of said plural radiating elements,
• λ is the free space wavelength at an imposed frequency f,
• ωce is the electron cyclotron frequency,
• ωpe is the electron plasma frequency, and
• φ, the phase difference between adjacent ones of said plural radiating elements, is measured in degrees.