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.

Imagine a jet engine that could propel an aircraft faster than a traditional engine, taking us all the way to the edge of the atmosphere, all without burning fossil fuels - and for a low cost.

That's exactly what plasma jet engines should be able to do, although thus far they have been confined to research labs, mostly those focusing on using the engines to move satellites and other spacecraft.

Now researchers from the Technical University of Berlin are working to bring them out of the lab and into the sky.  Instead of burning fuel and compressed air and then shoving the results out of the back of an engine to cause a forward propulsion, a plasma jet engine mimics a fusion reactor or a star.

It creates electricity by exciting and compressing gas into a plasma, and then generating an electromagnetic field. Led by Berkant Göksel, the research team aims to marry the plasma engine and the passenger jet to come up with something that could fly at very high altitudes but still take off and land.

Several obstacles are still standing between the plasma jet engine that can carry us to the edge of space and reality. First, Göksel's team was using tiny plasma thrusters - about 80 millimetres in length. It would take around 10,000 of these little thrusters to propel a standard commercial-size aircraft, so the current design is a non-starter. For now, Göksel's team intends to use 100 to 1,000 thrusters to move a smaller airship or plane, which ought to be feasible.

Like anything else that runs on electricity - especially something that needs so much electricity - the biggest problem that even the tiny version of the plasma thrusters face is the need for batteries. They need to be lightweight enough to avoid being counterproductive, yet have enough capacity to supply the needed power. The fact that the ultimate goal is making the thrusters bigger only exacerbates the issue.

So far, this problem hasn't been solved:

Göksel and his team are, thus far, relying on outside power breakthroughs to bridge this gap. Improvements in solar panels or compact fusion reactors for use on aircraft or spacecraft could be exactly what this system needs. Until something develops on that front, though, the team intends to create a hybrid craft that uses either rockets or pulse detonation combustion engines to fill in the gaps left by the plasma engine.