Nuno Loureiro: Probing the world of plasmas

Fusion, and specifically the physics of plasmas, has remained Nuno Loureiro&rsqu

Fusion, and specifically the physics of plasmas, has remained Nuno Loureiro’s primary research focus through graduate school, postdoc stints, and now in his research and teaching at MIT. Image: Jared Charney

Physicist explores the behavior of the universe’s most abundant form of matter.

Growing up in the small city of Viseu in central Portugal, Nuno Loureiro knew he wanted to be a scientist, even in the early years of primary school when "everyone else wanted to be a policeman or a fireman," he recalls.

His mother, now retired, taught Portuguese and French at the local high school, and his father was a lawyer. But by the time Loureiro finished high school, his interest in science had crystallized, and "I realized that physics was what I liked best," he says. During his undergraduate studies at the Technical University of Lisbon, he began to focus on fusion, which "seemed like a very appealing field," where major developments were likely during his lifetime, he says.

Fusion, and specifically the physics of plasmas, has remained his primary research focus ever since, through graduate school, postdoc stints, and now in his research and teaching at MIT. He explains that plasma research "lives in two different worlds." On the one hand, it involves astrophysics, dealing with the processes that happen in and around stars; on the other, it’s part of the quest to generate electricity that’s clean and virtually inexhaustible, through fusion power reactors.

Plasma is a sort of fourth phase of matter, similar to a gas but with the atoms stripped apart into a kind of soup of electrons and atomic nuclei. It forms about 99 percent of the matter in the universe, including stars and the wispy tendrils of material spread between them. Among the trickiest challenges to understanding the behavior of plasmas is their turbulence, which can dissipate away energy from a reactor, and which proceeds in very complex and hard to predict ways - a major stumbling block so far to practical fusion power.

While everyone is familiar with turbulence in fluids, from breaking waves to cream stirred into coffee, plasma turbulence can be quite different, Loureiro explains, because plasmas are riddled with magnetic and electric fields that push and pull them in dynamic ways. "A very noteworthy example is the solar wind," he says, an ongoing but highly variable stream of particles ejected by the sun and sweeping past Earth, sometimes producing auroras and affecting the electronics of communications satellites. Predicting the dynamics of such flows is a major goal of plasma research.

"The solar wind is the best plasma turbulence experiment we have," Loureiro says. "It’s increasingly well-diagnosed, because we have these satellites up there. That gives us relatively good access to it experimentally." By contrast, studying turbulence in plasma clouds in the interstellar medium, far out between the stars, doesn’t include the luxury of direct sampling, and must rely on more indirect observations and calculations. "There are no diagnostics whatsoever, other than from observational astronomy," he says.

Loureiro began concentrating on plasma physics in graduate school at Imperial College London, and continued this work during as a postdoc at the Princeton Plasma Physics Laboratory and later the Culham Centre for Fusion Energy, the UK’s national fusion lab. Then, after a few years as a principal researcher at the University of Portugal, he joined the MIT faculty at the Plasma Science and Fusion Center in 2015, where last year he earned tenure. A major motivation for moving to MIT from his research position, he says, was working with students. "I like to teach," he says.

Loureiro and his wife Ines, who does logistics work for museum art exhibits including the Institute of Contemporary Art and MIT’s List gallery, have three daughters, ages 12, 9, and 4.

His work at MIT has focused on a very specific area of plasma behavior, called magnetic reconnection. One example of this process occurs in the sun’s corona, a glowing irregular ring that surrounds the disk of the sun and becomes visible from Earth during solar eclipses. Vast loops of solar material are ejected from the surface, entrained in vortices of magnetic fields. Sometimes these magnetic fields become unstable and collapse back, unleashing a burst of energy as a solar flare. "That’s magnetic reconnection in action," he says.

Last year, Loureiro published a series of papers with physicist Stanislav Boldyrev at the University of Wisconsin, in which they proposed a new model to reconcile significant disparities between models of plasma turbulence and models of magnetic reconnection. So far, he says, with this new model, "the kinds of things we’re predicting here are actually in line with observations." Some aspects of it, however, may require new advances in observational technologies to be tested.

But the new concept, if proven, shows that magnetic reconnection must play a crucial role in the dynamics of plasma turbulence, at all scales, which is an insight that Loureiro and Boldyrev say would change the understanding of the dynamics and properties of space and astrophysical plasmas.

Loureiro says that a real understanding of turbulence in plasmas is essential for solving a variety of thorny problems in physics, from the way the sun’s corona gets heated to the structure of interstellar clouds to the dynamics of disks around black holes. And so he plugs away, using whatever tools may become available, to continue trying to unravel the complexities of plasma behavior.

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