The Little Plasma Engine That Could (Perhaps) Send Us to Other Worlds

James Maynard
Jan 29 · 4 min read

A new concept for a plasma engine that might, one day, drive machines — and people — to Mars and beyond.

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Fatima Ebrahimi, a principal researcher at Princeton Plasma Physics Laboratory, pictured in front of an artist’s concept of a spacecraft fitted with the new plasma engine design she envisions. Image credit: Elle Starkman (PPPL Office of Communications) and ITER

A plasma engine envisioned by a physicist at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) might carry us to Mars — and beyond — in spacecraft driven by the same forces that power solar flares.

Despite the Star Trek connotations, plasma engines are not a futuristic concept. Plasma engines are already being developed for space, but they provide a relatively small acceleration to spacecraft. Because of this, it would take an extremely long time for these craft to reach significant velocities.

This new design utilizes magnetic (rather than electric) fields, pushing particles of plasma (sometimes called the fourth state of matter) out an exhaust, providing propulsion.

A look at magnetic reconnections on the Sun. Video credit: NASA

This new design takes advantage of a process normally seen on the Sun — magnetic reconnection — the mechanism driving solar flares. During this process, magnetic fields converge, separate, and join once more, releasing vast amounts of energy. This same process also takes place in tokamaks — doughnut-shaped fusion reactors. Current designs for plasma engines use electricity to drive the particles out the exhaust, at much lower velocities.

Computer simulations show this new design could propel plasma at specific impulses (speeds) of hundreds of kilometers per second— 10 times faster than current plasma thrusters. A higher-specific impulse for plasma particles results in a higher initial velocity. This new design could bring robotic explorers and humans to Mars and beyond.

“I had the idea in 2017 while sitting on a deck and thinking about the similarities between a car’s exhaust and the high-velocity exhaust particles created by PPPL’s National Spherical Torus Experiment (NSTX). During its operation, this tokamak produces magnetic bubbles called plasmoids that move at around 20 kilometers per second, which seemed to me a lot like thrust,” Fatima Ebrahimi, a principal researcher at Princeton Plasma Physics Laboratory, explains.

Magnetism, you recall from physics class, is a powerful force that causes certain items to be attracted to refrigerators.
— Dave Barry

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A plasmoid seen within a solar filament in 2002. Image credit: ESA/NASA

This futuristic design for spacecraft engines offers three big advantages over current plasma thruster designs. The first is that using this new design, engineers will be able to adjust the thrust up and down, providing a throttle for the engine. The second difference is that this new design achieves additional thrust over current designs through the ejection of magnetic bubbles called plasmoids.

“Energetic thrust is generated in the form of plasmoids (confined plasma in closed magnetic loops)… Using a novel configuration of static electric and magnetic fields, the concept… continuously create[s] plasmoids via magnetic reconnection,” researchers describe in a paper published in the Journal of Plasma Physics.

The third difference from current models is that current plasma thrusters rely on the movement of heavy atoms such as xenon, this new design can use either light or heavy elements. This provides engineers with the chance to tailor the thrust of spacecraft for different purposes.

Our Sun, as well as other stars, is powered by nuclear fusion — the transformation of lighter elements into heavier ones, releasing energy. This is accomplished with elements in the form of a plasma — free nuclei (composed of protons and neutrons) and electrons. Plasma makes up 99 percent of all “ordinary” matter in the Cosmos.

Researchers are already constructing the first fusion reactors on Earth, but they still require far more energy to operate than they produce. However, once this breakeven point is achieved, this technology could deliver nearly limitless energy to the people of Earth.

“This work was inspired by past fusion work and this is the first time that plasmoids and reconnection have been proposed for space propulsion. The next step is building a prototype!” Ebrahimi exclaims.

To paraphrase Buzz Lightyear, “To Mars and Beyond!”

James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.

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