Sergey Macheret

Professor Sergey Macheret will receive a major recognition this July. His research has earned him the 2022 Plasmadynamics and Lasers Award from the American Institute of Aeronautics and Astronautics (AIAA) for “pioneering work on novel plasma generation and control methods and on aerospace applications of plasmas.” He was also elected an AIAA fellow earlier this year.

His specific contributions to the field began in the 1990s, when he worked to refute some original claims that plasmas behaved in ways that didn’t follow the conventional laws of physics. Macheret’s research contributed to the fundamental understanding of the physical mechanisms at work when plasmas are used for aerodynamic control – in part, the ability to reduce stall speeds by energizing the air moving over a wing, and to weaken shock waves in supersonic flight.

“We were not only putting together some general principles and limits, which were useful for the community, but specifically showing how using plasma with the proper set of parameters would improve high-speed, including hypersonic, vehicles.”

Macheret’s subsequent research into energy-efficient methods for producing plasmas led to discoveries that could produce more effective air-breathing engines for hypersonic aircraft.

Generating Efficiency

There are two ways of creating plasma, Macheret says. One is to heat a gas to very high temperatures, in the range of thousands up to millions of degrees. That takes copious amounts of energy and has limited aerospace applications. Fully ionized plasmas like these exist on the surface of the sun.

The other way to generate plasma is in a way similar to how a fluorescent light bulb works. Fluorescent bulbs, Macheret says, are a cold plasma, in which the gas overall remains at room temperature but the electrons themselves are raised to a very high energy by pumping electricity into the system.

The main challenge with this method is the amount of energy it takes to produce enough plasma for hypersonic applications.

“Starting from the late 1990s, a number of researchers, including me, have looked into various ways of reducing the power budget of sustaining a plasma with a certain high number of electrons per unit volume,” Macheret says.

He describes himself as a co-discoverer of a method that is now a mainstream way of creating and sustaining plasmas. “The technique is to apply a very, very strong electric field so that the ionization is very efficient, but only for a short period of time — on the order of nanoseconds,” he says.

The plasma generated this way begins to decay the instant the field is turned off, so they looked for ways to keep it going. Macheret and his colleagues determined that using short, repetitive pulses of this strong electric field sustains the plasma at a relatively high average electron density, at a low energy cost.

“Comparing to conventional plasmas generated by DC voltage, or AC voltage, or radio frequency voltage, in terms of watts per unit volume … we are able to reduce the power budget by two or three orders of magnitude,” Macheret says. “Coming up with this technique was one of my major contributions to generation and control of plasmas with high efficiency.”

Unintended Benefits

This technique makes plasma production more practical, but it has additional benefits beyond reducing the power bill of a plasma research lab.

During the electric field pulse, energized electrons can efficiently break molecules, such as O₂, into individual atoms. This is useful not only for applications such as microchip fabrication, but also for plasma-assisted combustion in aircraft engines.

“There are several difficulties in hypersonic air-breathing propulsion,” Macheret explains. “One is the air gets into the engine, with respect to the engine, the air moves at a velocity of several kilometers a second. That means we don't have much time in order to ignite the combustion, spread it, and complete the combustion normally. It’s not a very fast process.”

The normal workaround is to create a long and narrow engine, but Macheret says that’s a hugely inefficient design. Plasma-assisted combustion would allow for an entirely different approach.

“Once you have that atomic oxygen, you can start combustion very efficiently. It turns out that these nanosecond-pulse plasmas are very efficient in stimulating controlled combustion processes. In air-breathing hypersonic propulsion engines, or Scramjet engines, the plasma approach would enable relatively short and relatively wide engines, which dramatically increases efficiency.” Macheret says.

“This is mostly how people do plasma-assisted combustion today, and that includes experimental work here at Purdue by [Associate Professor] Sally Bane and her students, and in many, many other institutions.”

Producing Plasma Antennae

The future of Macheret’s research involves using weakly ionized plasmas for reconfigurable radio frequency systems and antennas, another area with huge potential impact in aircraft design.

“Modern airplanes can have dozens, and maybe even a hundred different antennas. Imagine the need to integrate all those antennas on the vehicle somehow. That drives the airplane design very significantly, and it compromises aerodynamics because you need to integrate antennas,” Macheret says.

The shape of an antenna is directly related to the type of signal it is trying to send or receive. Macheret’s current research hopes to demonstrate ways to combine many different antennas into a plasma aperture and to switch among different antennas electronically, similar to how an image on a multi-pixel plasma display panel can be rapidly changed.

Earned Recognition

The cautious nature of aircraft design and flight-approved manufacturing means that the work on plasma applications to aerospace vehicles remains in the theoretical and experimental phase for now. But Macheret’s decades of research into plasma generation and use has opened the door for these elements to improve the next generation of aircraft, which is why he’s being recognized this year by the AIAA.

Macheret is very proud that his contributions to the field resulted in this award. “I have played an important role in this community and in this area, and I know that everybody in that community knows me and my work. It’s something that is important to me. I’m happy to have received [the award], and I think that I deserve it.”