Could This Young Physicist Finally Crack the Code to Nuclear Fusion?
WHY YOU SHOULD CARE
Because this could help wean us off fossil fuels.
Amid the chaos of the Iran–Iraq War and its turbulent aftermath, Fatima Ebrahimi found her refuge in physics. As a teenager in the 1980s, she could do little more than observe the turmoil, but physics and its equations? That she could master. “Even if I was surrounded by all this craziness, it was a thing I could just do,” she tells OZY.
Now a physicist at the Princeton Plasma Physics Laboratory, Ebrahimi wants to bring order to another form of chaos: plasma, the electrically charged, superhot gas that makes up the sun. Deep inside the sun, plasma fuels nuclear fusion reactions, in which hydrogen atoms collide to form helium atoms, releasing massive amounts of energy. Ebrahimi’s research focuses on replicating that process on Earth in devices called tokamaks. Using computer simulations, she’s uncovering the physics behind a method she hopes will simplify the design of these devices, as well as reduce their size and cost, bringing us closer to creating a limitless supply of clean, renewable energy — the holy grail of energy research.
Most emissions of carbon dioxide, a major contributor to global warming, come from burning fossil fuels, used to power vehicles and generate electricity. “We desperately need another energy source that’s clean,” says Barrett Rogers, a theoretical and computational physicist at Dartmouth College. Ebrahimi’s fusion research “could be a breakthrough,” he says. And unlike nuclear fission — the splitting apart of atoms, which fuels today’s nuclear power plants — nuclear fusion doesn’t produce radioactive material.
[Physics is] like a piece of music that comes into your head …
To be sure, it’s early days yet. To make fusion power a reality, reactors need to generate more energy than they consume, which tokamaks have yet to do. And while Ebrahimi’s model of plasma “is definitely the right first step,” it’s “not the final step,” Rogers says. Plus, although several of her computer simulations have held up in lab experiments, others still require testing.
Ebrahimi, 46, has a broad smile and a full-throated laugh. A math whiz growing up, she was captivated by the notion of a unifying law of physics, an ever-elusive equation that could explain the entire universe. After studying physics at the Polytechnic University of Tehran, she knew she had to venture elsewhere to find success as a woman in science. In 2003, she earned a Ph.D. in plasma physics from the University of Wisconsin-Madison, with a focus on fusion, which she continued to investigate as a faculty member at the University of New Hampshire and, later, Princeton.
One goal of her research is to supersede the limitations of today’s conventional, doughnut-shaped tokamaks, which consist of a magnetic coil, or solenoid, resting within a central hole. An electric current runs through the solenoid, triggering another current in the plasma and generating a magnetic field that confines and heats the plasma. The extremely high temperatures — hundreds of millions of degrees Celsius — cause fusion to occur between hydrogen atoms in the plasma, releasing tons of energy. But, creating enough fusion to generate electricity requires a large solenoid and, therefore, a large tokamak. (For perspective, you could drive a tractor-trailer through a multibillion-dollar tokamak now under construction in France.) Plus, the current that flows through the plasma relies on ramping up the current in the solenoid; once that runs out, researchers need to deliver a fresh pulse of current to the solenoid, again and again.
As a workaround, Ebrahimi is investigating coaxial helicity injection (CHI), a method of starting fusion reactions that doesn’t involve solenoids, thereby simplifying the design of conventional tokamaks and making them both more compact and less costly. Instead of using a solenoid to generate a magnetic field, CHI involves injecting a magnetic field into the floor of the tokamak, removing the need to deliver periodic pulses of current. As it’s injected, the magnetic field — picture a series of concentric loops — inflates inside the tokamak. When a current runs through the magnetic field lines, they snap shut and pinch off, a process called magnetic reconnection, essentially forming a magnetic “balloon” filled with the current needed to fuel fusion while also confining the plasma.
Through computer simulations of CHI, Ebrahimi is studying its underlying physics, which could inform the design of future tokamaks. Her simulations suggest, for instance, that narrowing the bottom of the magnetic balloon that fills the tokamak creates a stronger current flowing through the plasma, making the device produce energy more efficiently. Conversely, she modeled regions at the edges of the plasma that can disrupt that current; understanding how this happens is key to preventing it. Now, she’s investigating whether CHI could allow tokamaks to run indefinitely, a major step toward making them commercially viable.
Beyond nuclear fusion, magnetic reconnection is behind a number of explosive phenomena, like solar flares. “It’s an area where people are making contributions,” says Adil Hassam, a professor of physics at the University of Maryland. “Ebrahimi and her colleagues will be among those at the forefront.”
Stewart Prager, Ebrahimi’s Ph.D. adviser and now a professor at Princeton, cites this intellectual drive as Ebrahimi’s major strength. “Her mind is always going in many directions.” But at the same time, he adds, she’s “always purposeful.”
It’s the sort of drive that keeps Ebrahimi awake late at night, churning away at her research. “[Physics is] like a piece of music that comes into your head,” she says. “Tomorrow the same thing comes, because it’s beautiful to you.”
Getting the world closer to infinite clean energy? Now that would be beautiful music.