According to the journal AIP Advances, which we get for the cryptic crossword, the idea of the research was to solve global warming problems owing to humans' use of fossil fuel combustion engines to power machinery, such as cars and airplanes.

Author Jau Tang, a professor at Wuhan University, said: "There is no need for fossil fuel with our design, and therefore, there is no carbon emission to cause greenhouse effects and global warming."

The method involves using an aggregate of charged ions which can be generated by compressing air into high pressures and using a microwave to ionize the pressurised air stream.

Other plasma jet thrusters, like NASA's Dawn space probe, use xenon plasma, which cannot overcome the friction in Earth's atmosphere, and are therefore not powerful enough for use in air transportation. Instead, the authors' plasma jet thruster generates the high-temperature, high-pressure plasma in situ using only injected air and electricity.

The prototype plasma jet device can lift a 1-kilogram steel ball over a 24-millimeter diameter quartz tube, where the high-pressure air is converted into a plasma jet by passing through a microwave ionization chamber. To scale, the corresponding thrusting pressure is comparable to a commercial airplane jet engine.

By building a large array of these thrusters with high-power microwave sources, the prototype design can be scaled up to a full-sized jet. The authors are working on improving the efficiency of the device toward this goal.

"Our results demonstrated that such a jet engine based on microwave air plasma can be a potentially viable alternative to the conventional fossil fuel jet engine", Tang said.