Electrodeless plasma thruster

Operating principle

1. Propellant is injected at the upstream side of the thruster body. In case the propellant used is not gaseous (e.g. alkali metals) at the local temperature it is where this propellant must be vaporized.
2. Gaseous propellant is ionized by one of the following methods. Gaseous propellant can be ionized by bombarding it with electrons emitted by a hot cathode or an electron gun. Another possible method can be to use a steady state discharge between two electrodes. Ionization can also be performed by applying an alternating electric field either via a lower hybrid oscillation, to produce a high density cold plasma.
3. The cold and dense plasma, produced by the ionization stage, then drifts toward the acceleration stage by diffusion across a region of higher magnetic field intensity.
4. In the acceleration stage the propellant plasma is accelerated by magnetized ponderomotive force in an area where both non-uniform static magnetic field and non-uniform high-frequency electromagnetic fields are applied simultaneously.

Advantages

This thruster technology can deliver large thrust density as the acceleration process is not limited by plasma density through Hall Parameter or grid electrical screening. Further as the ponderomotive force accelerate all plasma species in the same direction, this thruster technology does not need any neutralizer. The fact that electrodeless plasma thruster is inherently multi-staged allow to optimize separately both stages or to throttle the thruster at constant power between higher specific impulse and higher thrust. Last the field of ponderomotive force is created by non-uniform high frequency field and static magnetic field thus it implies no grids or contact between the plasma and any electrodes hence avoiding most thruster erosion and spacecraft contamination issues.

Applications

Propulsion systems based on electrodeless plasma thrusters seems ideally suited for orbit raising for large geostationnary satellite, and would also be able to perform station keeping, hence enabling important propellant mass saving. The ability of this technology to provide large thrust density could allow faster missions to outer planets.

Other researches

The use of ponderomotive force to accelerate a plasma has recently been investigated from a theoretical point of view by Princeton Plasma Physics Laboratory scientists I. Y. Dodin, Y. Raitses and N. J. Fisch.

Some theoretical researches have also been reported around the debated issue of the existence of a double layer in such thruster, even if such a double layer structure would be current-free, as both ions and electrons travels in the same directions at the same average terminal speed, and the existence of current free double layer is still debated among plasma physicists.

See also

• Spacecraft propulsion
• Magnetic sail
• Hall effect thruster
• VASIMR
• Magnetoplasmadynamic thruster
• Field Emission Electric Propulsion
• Helicon Double Layer Thruster
• Ion thruster
• Pulsed inductive thruster