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Fusion reactors are now seen as the heat source that could bring the rocket thruster to an extremely high temperature (and therefore high-speed exhaust) or expel ultra-hot plasma to provide thrust. Credit: ITER
A new type of rocket thruster that could lead mankind to March and beyond was proposed by a physicist at the Princeton Plasma Physics Laboratory of the US Department of Energy (DOE) (PPPL).
The device would apply magnetic fields to cause plasma particles(the link is external), an electrically charged gas also known as the fourth state of matter, to pull the rear of a rocket and, due to conservation of momentum, propel the craft forward. Proven in today’s space plasma thrusters use electric fields to propel the particles.
The new concept would accelerate particles using magnetic reconnection, a process found throughout the universe, including the surface of the sun, in which magnetic field lines converge, suddenly separate, and then come together, producing a lot of energy. . Reconnection also occurs inside the donut-shaped fusion(the link is external) devices called tokamaks(the link is external).
“I’ve been cooking this concept for quite some time,” said Fatima Ebrahimi, PPPL senior research physicist, concept inventor and article author.(the link is external) detailing the idea in the Journal of Plasma Physics. “I got the idea in 2017 sitting on a bridge and thinking about the similarities between a car’s exhaust and the high-speed exhaust particles created by PPPL’s National Spherical Torus Experiment (NSTX) , ”The precursor of the laboratory’s current flagship fusion facility. “During its operation, this tokamak produces magnetic bubbles called plasmoids which travel at about 20 kilometers per second, which seemed to me a bit like a push.
Fusion, the power that drives the sun and stars, combines light elements in the form of plasma – the hot, charged state of matter made up of free electrons and atomic nuclei that make up 99% of the visible universe – to generate massive amounts of energy. Scientists seek to replicate fusion on Earth for a virtually inexhaustible supply of energy to generate electricity.
Current plasma thrusters that use electric fields to propel the particles can only produce a small specific impulse, or velocity. But computer simulations performed on PPPL computers and the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility at the Lawrence Berkeley National Laboratory in Berkeley, Calif., Have shown that the new concept of the plasma thruster can generate gas from the plasma. ‘exhaust with speeds of hundreds of kilometers per second, 10 times faster than those of other thrusters.
This faster speed at the start of a spacecraft’s journey could bring the outer planets within reach of astronauts, Ebrahimi said. “Long-distance travel takes months or years because the specific impulse of chemical rocket engines is very low, so the craft takes a while to level up,” she said. declared. “But if we make thrusters based on magnetic reconnection, then we could perform long-range missions in a shorter time frame.”
There are three main differences between Ebrahimi’s thruster concept and other devices. The first is that changing the strength of magnetic fields can increase or decrease the amount of thrust. “By using more electromagnets and more magnetic fields, you can actually turn a knob to fine tune the speed,” Ebrahimi said.
Second, the new propellant produces motion by ejecting both plasma particles and magnetic bubbles called plasmoids. Plasmoids add power to the propulsion and no other propellant concept integrates them.
Third, unlike current thruster concepts which rely on electric fields, the magnetic fields of Ebrahimi’s concept allow the plasma inside the thruster to consist of heavy or light atoms. This flexibility allows scientists to tailor the amount of thrust for a particular mission. “While other thrusters require heavy gas, made up of atoms like xenon, in this concept you can use any type of gas you want,” Ebrahimi said. Scientists may prefer light gas in some cases because the smaller atoms can move faster.
This concept expands PPPL’s space propulsion research portfolio. Other projects include the Hall Thruster Experiment which was started in 1999 by PPPL physicists Yevgeny Raitses and Nathaniel Fisch to study the use of plasma particles to move spacecraft. Raitses and the students are also studying the use of tiny Hall-effect thrusters to give small satellites called CubeSats greater maneuverability as they orbit the Earth.
Ebrahimi pointed out that his propellant concept stems directly from his research on fusion energy. “This work was inspired by past fusion work and this is the first time that plasmoids and reconnection have been proposed for space propulsion,” Ebrahimi said. “The next step is to build a prototype!”
Reference: “An Alfvenic reconnecting plasmoid thruster” by Fatima Ebrahimi, December 21, 2020, Journal of Plasma Physics.
DOI: 10.1017 / S0022377820001476
Support for this research came from the DOE Office of Science (Fusion Energy Sciences) and Laboratory Directed Research and Development (LDRD) funds made available by the Office of Science.
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