Plasma Jets May One Day Propel Aircraft

Plasma thrusters could help jet planes fly without fossil fuels

2 min read
A steel ball can get suspended in the air by the pressure from a plasma jet.
A steel ball can be suspended in the air by the pressure from a plasma jet.
Image: Jau Tang and Jun Li/AIP

Jet planes may one day fly without fossil fuels by using plasma jets, new research from scientists in China suggests.

A variety of spacecraft, such as NASA’s Dawn space probe, generate plasma from gases such as xenon for propulsion. However, such thrusters exert only tiny propulsive forces, and so can find use only in outer space, in the absence of air friction.

Now researchers have created a prototype thruster capable of generating plasma jets with propulsive forces comparable to those from conventional jet engines, using only air and electricity.

An air compressor forces high-pressure air at a rate of 30 liters per minute into an ionization chamber in the device, which uses microwaves to convert this air stream into a plasma jet blasted out of a quartz tube. Plasma temperatures could exceed 1,000 °C.

“We could lift a steel ball weighing about 1 kilogram using only about 400 watts of microwave power,” says Jau Tang, a physicist at Wuhan University in China and senior author of a new study describing the work.

The scientists estimated the jet pressure from their device reached 2,400 newtons per square meter, comparable to that from a commercial airplane jet engine. “This result surprised me,” Tang says. “It means that if we could scale up the microwave power and the compressed air inlet stream to the standard of an actual jet engine, we could have the same strength of jet propulsion using only electricity and air but no fossil fuel.”

If air plasma jets ever become practical, they could reduce fossil fuel use and greenhouse gas emissions, the researchers say. According to the U.S. Environmental Protection Agency, aircraft contribute 12 percent of U.S. transportation emissions, and account for 3 percent of the nation's total greenhouse gas production. Globally, aviation produced 2.4 percent of total carbon dioxide emissions in 2018.

“We are quite excited that only electricity and air are needed,” Tang says. “We do not need fossil fuels to power a jet engine.”

A schematic diagram of a prototype microwave air plasma thruster and the images of the bright plasma jet at different microwave powers. This device consists of a microwave power supply, an air compressor, a compressed microwave waveguide and a flame ignitor. A schematic diagram of a prototype microwave air-plasma thruster and images of the bright plasma jet at different microwave powers. This device consists of a microwave power supply, an air compressor, a compressed microwave waveguide, and a flame igniter. Image: Jau Tang and Jun Li/AIP

All in all, “I think that within five years, one could use a scaled-up plasma engine to power small pilotless airplanes or heavy-duty drones to carry cargo for shipping,” Tang says. “For an air-plasma engine to power a large jumbo jet, it would require a large array of megawatt microwave sources, high-power turbine compressors, and an extremely high electric energy storage capability. I guess that development could take another decade.”

The scientists are currently focused on scaling up the power of the system. If they can build a megawatt-strength plasma engine capable of driving a real airplane, they will then “pay attention on ways to reduce weight and size,” Tang says.

The scientists detailed their findings on 5 May in the journal AIP Advances.

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​​Why the World’s Militaries Are Embracing 5G

To fight on tomorrow's more complicated battlefields, militaries must adapt commercial technologies

15 min read
4 large military vehicles on a dirt road. The third carries a red container box. Hovering above them in a blue sky is a large drone.

In August 2021, engineers from Lockheed and the U.S. Army demonstrated a flying 5G network, with base stations installed on multicopters, at the U.S. Army's Ground Vehicle Systems Center, in Michigan. Driverless military vehicles followed a human-driven truck at up to 50 kilometers per hour. Powerful processors on the multicopters shared the processing and communications chores needed to keep the vehicles in line.

Lockheed Martin

It's 2035, and the sun beats down on a vast desert coastline. A fighter jet takes off accompanied by four unpiloted aerial vehicles (UAVs) on a mission of reconnaissance and air support. A dozen special forces soldiers have moved into a town in hostile territory, to identify targets for an air strike on a weapons cache. Commanders need live visual evidence to correctly identify the targets for the strike and to minimize damage to surrounding buildings. The problem is that enemy jamming has blacked out the team's typical radio-frequency bands around the cache. Conventional, civilian bands are a no-go because they'd give away the team's position.

As the fighter jet and its automated wingmen cross into hostile territory, they are already sweeping the ground below with radio-frequency, infrared, and optical sensors to identify potential threats. On a helmet-mounted visor display, the pilot views icons on a map showing the movements of antiaircraft batteries and RF jammers, as well as the special forces and the locations of allied and enemy troops.

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