Breakthrough In Next-Generation Plasma Engine

An ion engine that uses heavy charged particles for propulsion. NASA/JPL-Caltech

Plasma engines can’t get us to space yet, but they are extremely useful in that they can deliver a large thrust with very little fuel. The plasma engines do their job, but they have plenty of room for improvement. Now, a team at Tohoku University have cracked one of its problems.

Plasma is made of charged particles, which means it can be manipulated with magnetic fields. However, this sophisticated type of engine uses a magnetic nozzle, which wasn’t working as expected. In a paper published in Physical Review Letters, Kazunori Takahashi and Akira Ando have worked out how to overcome the issue.

The magnetic nozzle helps to compress the plasma so that it can reach a higher velocity as it leaves the engine. Unfortunately, the magnetic field is shaped in such a way that the plasma curves back in on itself and ends up producing a net thrust of zero.

The proposed solution was to stretch the field lines in such a way that the plasma can escape into space in a very narrow direction. But changing the magnetic field of a plasma engine is not an easy task. In this case, the plasma itself was useful in changing it.

Moving charged particles generate a magnetic field, so the Japanese researchers used the plasma to change the overall magnetic field of the system. With this approach, the team was able to create and observe the stretching magnetic field.

The variation was just a few percent of the magnetic field created in the nozzle, but this is a solid first step in addressing the bigger issue in this type of plasma engine. Researchers also discovered that the stretching field can be obtained by expelling particles at a lower velocity than expected.

The research bridges a significant gap in knowledge between plasma out there in the universe and what we have tested in the lab. Most matter in the universe is in a plasma state, although it’s rare here on Earth. Understanding plasma better is more than just for space exploration.

Missions like Dawn, which is studying Ceres, have already used the emission of charged particles to propel themselves. There is still a lot to do before a plasma engine with this stretch field becomes commonplace in deep space vehicles, but we are (slowly) getting there.

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