Improved performance of electrodeless plasma thrusters for space propulsion

A researcher at Tohoku University has increased the performance of a high-powered electrodeless plasma thruster, bringing us one step closer to exploring deeper in space.

Innovations in ground transportation technologies, such as cars, trains, and planes, have so far driven historic technologies and industries; now, a similar breakthrough is occurring in space through electric propulsion technology.

Electric propulsion is a technique using electromagnetic fields to accelerate a thruster and generate thrust that propels a spacecraft. Space agencies have pioneered electric propulsion technology as the future of space exploration.

Already, several space missions have been successfully completed using electric propulsion devices, such as grid ion thrusters and Hall thrusters. Solar energy is converted into thrust energy when the thruster becomes ionized, i.e. plasma, and is accelerated by electromagnetic fields. However, the electrodes necessary for these devices limit their lifetime, because they are exposed and damaged by the plasma, in particular at a high power level.

To circumvent this, scientists turned to electrodeless plasma thrusters. One such technology uses radio frequency (rf) to generate plasma. An antenna radiates radio waves into a cylindrical chamber to create plasma, where a magnetic nozzle channels and accelerates the plasma to generate thrust. MN RF plasma thrusters, or helicon thrusters as they are sometimes called, offer simplicity, operational flexibility and a potentially high thrust-to-power ratio.

But the development of MN RF plasma thrusters has been hampered by the efficiency of converting RF power to thrust energy. Early experiments generated single-digit conversion rates, but more recent studies have reached a modest 20%.

In a recent study published in Scientific reportsProfessor Kazunori Takahashi from the Electrical Engineering Department of Tohoku University achieved a conversion efficiency of 30%.

While mature electric propulsion devices often use xenon gas, which is expensive and difficult to supply in sufficient quantity, the current efficiency of 30% has been achieved with an argon propellant. This indicates that an RF MN plasma thruster would reduce the cost and burden on Earth’s resources.

“Applying a cusp-like magnetic field inhibited the energy loss that typically occurs at the wall of the plasma source,” Takahashi said. “This breakthrough opens the door to advances in high-powered space transportation technology.”