The Innovative Dual-Stage 4-Grid Ion Thruster Concept – Theory And Experimental Results
- Paper number
IAC-06-C4.4.07
- Author
Dr. Cristina Bramanti, European Space Agency (ESA), The Netherlands
- Coauthor
Dr. Roger Walker, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Dr. David G. Fearn, EP Solutions, United Kingdom
- Coauthor
Dr. Orson Sutherland, Australia
- Coauthor
Ms. Marika Orlandi, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Mr. Jose Gonzalez del Amo, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Prof. Rod Boswell, Australia
- Coauthor
Dr. Christine Charles, Australia
- Year
2006
- Abstract
A new concept for an advanced Dual-Stage 4-Grid (DS4G) ion thruster has been proposed which draws inspiration from Controlled Thermonuclear Reactor (CTR) experiments. For over 20 years, ion sources, coupled with charge-exchange gas cells, have been used to inject highly energetic neutral particles (80-100 keV) into fusion reactor experiments. These ion sources are remarkably similar in design to gridded ion thrusters (without external neutraliser) with the exception that they use 4-grid systems in order to achieve extremely high ion velocities with light gases such as hydrogen. This 4-grid configuration allows the ion extraction and ion acceleration processes to be decoupled, essentially creating a dual-stage system instead of the usual three grid thrusters where the two processes must occur simultaneously, leading to a practical limitation in the maximum beam potential to <5 kV. In the first stage of the 4-grid concept, ions are extracted from the discharge chamber using the first two grids with the potential limited to <5kV to prevent excessive plasma sheath curvature and hence direct impingement of the extracted ions on the grids. Then, in a longer second stage between the two pairs of grids, they are accelerated to much higher velocities with acceleration potentials of up to 80 kV. Due to the high beam potential, the 4-grid ion thruster concept is theoretically able to deliver substantial improvements in propulsive performance over the current state-of-the-art gridded ion engines in terms of specific impulse, power and thrust density, maximum power and beam divergence at the cost of a higher specific power. For example, a single 20 cm diameter 4-grid ion thruster could operate at 250 kW power to produce a 2.5 N thrust and a specific impulse of 19,300 s using Xenon propellant operating at a 30 kV beam potential with a 1 mm extraction grid separation.
Given this promising concept, a small laboratory prototype thruster was developed and built to ESA requirements by ANU, and its performance was measured during two extensive test campaigns conducted in a large vacuum facility at the ESA Propulsion Laboratory. The principal goals of the laboratory experiments were to prove the practical feasibility of the overall concept, demonstrate the high performance predicted by analytical and simulation models, and investigate critical design parameters and technological challenges in preparation for any future spacecraft thruster development activities. The lab prototype DS4G thruster was designed to operate at beam potentials of up to 30kV with Xenon propellant using an RF plasma discharge and employing various grid designs. Target performances were specific impulse of 19,000 s, open area power density of 900 W/cm2, open area thrust density of 9 mN/cm2, efficiency >60
- Abstract document
- Manuscript document
IAC-06-C4.4.07.pdf (🔒 authorized access only).
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