Fiery sun

Eugenio Schuster and Arindam Banerjee Explore Two Paths to Creating Sustainable Energy

Lehigh researchers study two approaches to achieving and maintaining nuclear fusion: magnetic confinement and inertial confinement.

Story by

Lori Friedman

Videography by

Stephanie Veto

Nuclear fusion may be the answer to the world’s energy challenges—if scientists can figure out how to sustain this nuclear reaction on Earth.

 A nuclear fusion reaction is very different from a nuclear fission reaction, which has been the mechanism used in nuclear power plants to produce energy since the 1950s.

Fission involves splitting the nuclei of very heavy elements, such as uranium and plutonium. This starts a chain reaction that is difficult to slow, which is one of the reasons it can be dangerous.

Nuclear fusion, on the other hand, uses some of the lightest elements, such as hydrogen, to generate energy—and is a reaction that is very difficult to spur and maintain.

Research in this area has been going on for more than sixty years. However, scientists have yet to achieve sustained energy generation through fusion. Some believe that success may be just around the corner—an achievement that would be a boon for humankind and the planet. The energy generated by fusion could be enough to meet all of the world’s energy needs for many years to come.

Fusion seeks to generate energy the way the sun does. The sun creates energy in the form of light and heat by fusing atoms of hydrogen, using its massive gravitational force to overcome the hydrogen ions’ natural tendency to repel each other. Nuclear fusion on Earth tries to mimic this process, but other mechanisms are needed to overcome the repulsion between hydrogen ions and confine the hot gas called plasma.

Researchers have zeroed in on the two most promising paths to achieving and maintaining fusion: magnetic confinement and inertial confinement. Lehigh’s engineering faculty are working on both.

The blue haze of a hydrogen isotope plasma

The blue haze of a hydrogen isotope plasma

Answering Burning Questions to Control ‘Burning Plasma’

Eugenio Schuster, a professor of mechanical engineering and mechanics, studies how to control magnetically confined nuclear-fusion plasmas. In this method, two isotopes of hydrogen—deuterium and tritium—are heated up to 100 million Kelvin, which is approximately six times hotter than the suns core. At this temperature the ions have enough kinetic energy to overcome repulsion and fuse. Because this is much too hot to be contained by any ordinary material, scientists use magnetic fields to confine the “burning plasma” that results. The reaction takes place in a toroidal-shaped (like a ring-shaped donut) apparatus. The device is a Russian invention called “tokamak.” 

“We are dynamicists,” says Schuster, describing the role of researchers like him working on ways to stabilize and control the heated plasma. “What we do is to try to understand the plasma’s dynamics, coming up with equations to model its behavior, particularly in response to different types of actuators such as magnetic coils, neutral beam injectors, radio-frequency wave launchers and fueling valves. But we don’t stop there. We want to modify the actuation to create the dynamics we want. We want control.”

Schuster and his team regularly conduct experiments on a number of tokamaks around the world. These include DIII-D in San Diego, where members of his group are permanently stationed, as well as NSTX-U in Princeton, EAST in China and KSTAR in South Korea.

Last year, Schuster was named to the prestigious ITER Scientist Fellows Network. ITER (“The Way” in Latin) is a nuclear fusion facility being built in southern France. It is a global collaboration that aims “to build the world’s largest tokamak, a magnetic fusion device that has been designed to prove the feasibility of fusion as a large-scale and carbon-free source of energy based on the same principle that powers our sun and stars.” The collaboration involves 35 nations and is led by ITER members: China, the European Union, India, Japan, Korea, Russia and the United States.

As part of the network, Schuster works closely with scientific collaborators and ITER to address key research and development issues as the facility prepares for its operational phase.

The U.S. Department of Energy also named Schuster an expert member of the Integrated Operation Scenarios Topical Group within the International Tokamak Physics Activity, the task of which is to contribute to establishing operational scenarios in burning plasma experiments, particularly candidate scenarios in ITER.

“Currently, nuclear fusion reactors do not produce energy,” says Schuster. “The experiments done on tokamaks around the world are focused solely on studying the physics of the plasma.”

Artist's concept view of the interior of the ITER reaction vessel

Artist's concept view of the interior of the ITER reaction vessel

ITER seeks to be the first tokamak to demonstrate efficient net energy production via nuclear fusion by creating and sustaining the reaction for a long duration so it can be a reliable energy source. The goal, says Schuster, is to produce ten times more energy than is injected into the tokamak plasma. ITER is scheduled to start operating by late 2025. 

“Deuterium may be readily extracted from ordinary water, which is available to all nations. Tritium does not occur naturally but would be produced from lithium, which is available from land deposits or from sea water which contains thousands of years’ supply,” says Schuster. “Unlike fossil fuels, nuclear fusion produces no air pollution or greenhouse gases, since the reaction product is helium.”

In other words, the work that Schuster and his colleagues are doing at ITER and other facilities could bring the world closer to a carbon-free, combustion-free future.

Understanding the hydrodynamics of inertial confinement

Arindam Banerjee, an associate professor of mechanical engineering and mechanics, studies fluid dynamics in extreme environments—and it would be hard to find a more extreme environment than the one needed to achieve fusion.

The Rotating Wheel Rayleigh Taylor Instability Experiment, a device Banerjee and his team built to mimic the conditions of inertial confinement.

The Rotating Wheel Rayleigh Taylor Instability Experiment, a device Banerjee and his team built to mimic the conditions of inertial confinement. 

Banerjee works on a method known as inertial confinement. In the U.S., the two major labs for this research are the National Ignition Facility at the Lawrence Livermore National Laboratory in Livermore, California—the largest operational inertial confinement fusion experiment in the U.S.—and the Los Alamos National Laboratory in New Mexico. Banerjee works with both.

He and his team are trying to understand the fundamental hydrodynamics of the fusion reaction, as well as the physics.

In inertial confinement experiments, the gas (hydrogen isotopes, like in magnetic fusion) is frozen inside pea-sized metal pellets. The pellets are placed in a chamber and then hit with high-powered lasers that compress the gas and heat it up to a few million Kelvin—about 400 million degrees Fahrenheit—creating the conditions for fusion.

The massive transfer of heat, which happens in nanoseconds, melts the metal. Under massive compression, the gas inside wants to burst out, causing an unwelcome outcome: The capsule explodes before fusion can be reached. One way to understand this dynamic, explains Banerjee, is to imagine a balloon being squeezed.

“As the balloon compresses, the air inside pushes against the material confining it, trying to move out,” says Banerjee. “At some point, the balloon will burst under the pressure. The same thing happens in a fusion capsule. The mixing of the gas and molten metal causes an explosion.”

To prevent the mixing, adds Banerjee, you have to understand how the molten metal and heated gas mix in the first place.

To do this, his group runs experiments that mimic the conditions of inertial confinement, isolating the physics by removing the temperature gradient and the nuclear reactions.

Banerjee and his team have spent more than four years building a device specifically for these experiments. It looks like a high-speed train track in a figure-eight shape. Housed on the first floor of Lehigh’s Packard Laboratory, the experiment will be the only of its kind in the world, as it can study two-fluid mixing at conditions relevant to those in inertial confinement fusion. State-of-the-art equipment is also available for diagnosing the flow. The projects are funded by the Department of Energy, Los Alamos National Laboratory and the National Science Foundation.

Interestingly, one of the ways that researchers like Banerjee mimic the molten metal is by using mayonnaise. The material properties and dynamics of the metal at a high temperature are much like those of mayonnaise at low temperature, he says.

The team’s device re-creates the incredible speed at which the gas and molten metal are mixing. They gather data from the experiments they run and then feed it into a model being developed at Los Alamos National Lab.

Banerjee and his students developed the Rotating Wheel Rayleigh Taylor Instability Experiment, an experiment that studies two-fluid mixing to mimic inertial confinement fusion. The lab, known as the Turbulent Mixing Laboratory, took Lehigh students five years to build from scratch.

Turbine

Banerjee was awarded a three-year grant from the National Science Foundation to study the impact of free-stream turbulence on tidal turbines. 

Turning the Tide in Renewable Energy Use

Hydropower technologies, which use the flow of water to generate electricity, have great potential to change the renewable energy landscape in the United States. First, tides are more predictable than the wind or sun. Additionally, more than 50 percent of the U.S. population lives within 50 miles of a coastline.

There are only a few commercialized power plants in the world that harness the natural tides of an existing body of water, utilizing what is known as tidal energy—and none of these are in the U.S. Engineers are still working to improve the technology of tidal energy generators to increase the amount of energy they produce, making it cheap enough for consumers to use and profitable enough for companies to invest in.

In New York, Verdant Power is poised to become the first U.S. company to generate electricity through tidal power. The Federal Energy Regulatory Commission (FERC) recently issued to Verdant a hydrokinetic pilot project license—the first commercial license issued for a tidal power project in the U.S. The project, called the Roosevelt Island Tidal Energy (RITE) Project, consists of 30 tidal turbines currently underwater in New York City’s East River. It is the only project of its kind in the nation.

Arindam Banerjee and his team are applying their expertise in multi-scale fluid dynamics as they work with Verdant to help make sustainable tidal energy generation a reality.

“Most of the work my lab does is on renewable energy,” says Banerjee. “We study next-generation water turbines—turbines that are going to be put in a river or wave energy converters that will be used to harness energy from flowing rivers, tides and oceans.”

Banerjee was awarded a three-year grant from the National Science Foundation (NSF) to study the impact of free-stream turbulence on tidal turbines. He recently received a supplemental “internship” grant for one of his Ph.D. students to work full-time on-site at Verdant.

According to Banerjee, tidal turbines are a relatively new class of renewable energy device. He and his team are working with Verdant on ways to improve the performance and durability of their turbines.

“My research is focused on addressing several outstanding scientific challenges that need to be overcome so that these novel devices can be developed and deployed,” says Banerjee. 

Banerjee and his team test the devices using turbulence generation techniques to mimic hydraulic and natural in-stream conditions. Diagnostics include a reaction torque-thrust sensor for system analysis and time-resolved stereo particle image velocimetry for flow-field measurements. 

“A detailed understanding of the evolution of the wake turbulence is vital when considering the design of an underwater tidal farm, similar to wind farms on land,” says Banerjee. 

The potential of tidal energy is vast. If performance issues can be solved and tidal energy commercialized, it may be possible to generate 300 terawatt-hours per year (TWh/year) in the U.S. through tidal energy. That would be enough to power roughly 27 million homes­­—an achievement that could turn the tide in renewable energy use in the U.S. 

This story originally appeared as "Making Energy Like the Sun" in the 2019 Lehigh Research Review.

Story by

Lori Friedman

Videography by

Stephanie Veto

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