Out of This World with Lexington Resident Richard Petrasso

Lexington resident and MIT Senior Research Scientist Richard Petrasso works in a world whose dimensions are almost impossible to fathom. 

0.000000001 (one billionth)

0.0036609 (thirty-six thousand six hundred nine ten-millionths)

500,000,000,000 (500 billion)

His everyday vocabulary is equally out of this world. 

Fusion (“when two atoms slam together to form a heavier atom…. the same process that powers the sun and creates huge amounts of energy.” — U.S. Department of Energy)

Thermodynamic temperature (an absolute measure of the average total internal energy of an object or objects)

Joule (a unit of energy defined in the most pedestrian terms as the energy required to lift a small apple one meter straight up).

Even Petrasso’s former title is hard to comprehend: Director of MIT’s Plasma Science and Fusion Center (PSFC)’s High-Energy-Density Physics (HEDP) Division.

What is clear, however, is the extraordinary achievement of Petrasso and his team at 1:00 a.m. on Dec. 5, 2022 at Lawrence Livermore National Laboratory in California.

In what U.S. Secretary of Energy Jennifer Granholm called “one of the most impressive scientific feats of the 21^st century” — what she joked President Biden might call “a BFD” — the international group successfully created fusion ignition in a laboratory. To wit, they created more energy than was required to catalyze the process, unlocking the potential for large-scale development of zero-carbon, clean energy. “Ignition allows us to replicate for the first-time certain conditions that are only in the stars and the sun,” Secretary Granholm explained.

Petrasso has been fascinated by fusion, and the stars and the sun, since “the time I could start to think and talk … you know very early,” he says. The periodic table was a particular point of interest. “To this day, the periodic table sits in my memory. You can name me any number, and I can give you the element and all its characteristics.” Little wonder he won the state science fair in seventh grade, besting kids many years his senior. The signs were there.

When asked to reflect on the Dec. 5 achievement, Petrasso notes that it bears “a strong or appropriate analogy to the Wright Brother’s first flight … Just as they demonstrated the feasibility of flight, the experiment … demonstrated that it is in fact realizable to obtain more fusion energy out … than the laser energy input.”

Trying to describe the experiment in simple language, he starts with the equipment. There was “a miniscule pepper-corn sized capsule, filled with special hydrogen” — also known as heavy hydrogen, made up of the elements deuterium and tritium — encased in a small, can-like capsule known as a hohlraum, named for the German word for “hollow space,” that focuses radiation. 

Petrasso holds up a picture of a hohlraum that has light beams streaming out of each end. On Dec. 5, his team blasted a total of “2 million joules of laser energy” — similar in force to a pound of TNT — into the two ends of just such a capsule, creating a veritable “shower of radiation, bathing the capsule,” and creating an unimaginably hot compression process. 

It sounds simple enough. But the MIT senior scientist likens the inherent difficulty of the compression to trying to squeeze a large blob of Jello in your hands down to the size of a pea without losing any through your fingers: “We’re basically compressing a basketball down to a pea.” And the final “legume” has to be in perfect proportion to the original object. “It’s incredibly hard,” he admits. “That’s why it’s taken us 50 years.”

Petrasso’s voice rises with excitement as he recalls the heat produced by the process. “The temperature of the hydrogen fuel reached 150 million degrees Celsius,” he marvels, “and the density was 500 times larger than that of water. These unique conditions far exceed that at the center of our sun (i.e., 15 million degrees Celsius, and a density of 160 times that of water).”

What made the experiment most remarkable — and promising — though, was that three million joules were created from a basis of two million joules of laser energy, a condition that exceeded “fusion breakeven,” a milestone never before been achieved in a lab. According to Petrasso, “it all happened in 100 picosec, that is in 100 trillionths of a second or, alternatively, 1/10 of a billionth of a second.”

For practical purposes, Petrasso and his colleagues still have a way to go before the method can be applied to everyday life at any meaningful scale. As a start, they will have to produce considerably more fusion energy; the experiment’s output, he notes, may sound like a lot but energy-wise, is only equivalent to running a 1000-watt microwave continuously for 50 minutes. And there are other, major technical issues that have to be resolved, as well, like how to efficiently capture the energy and convert it to electricity, and the use of much more efficient lasers.

Still, the breakthrough suggests promise, not just for a clean energy future but for a safer world. As Secretary Granholm noted in her Jan. 24 press conference, fusion ignition “strengthens our national security because it opens a new realm for maintaining safe, secure and effective nuclear deterrence in an age where we do not have nuclear testing.” In the absence of testing, Petrasso says, “the question remains … if you take your car and you put it in your garage for 30 or 40 years,” how will you know that it works? The analogy holds true for weapons, as well. Finally, there is also the upside of being the first to reach this goal. “Let me say this,” Petrasso says emphatically, “I am tremendously happy that the U.S. and the National Ignition Facility achieved this success … and not [Russia and China].”

For a man who lives with his mind trained on what can seem like another world, how does the scientist manage to keep his feet on the ground? “It’s very hard,” he chuckles before confessing, “sometimes, I really prefer being in that conceptual world, in part because when you see a lot of the news is so filled with stressful things … science becomes a haven.” He particularly relishes the camaraderie that his work brings. “Working with my fellow scientists is a great love and great privilege … science to me is just really just a wonderful social enterprise because it has stimulating ideas [and] this incredible social thread that underpins everything that’s there.”

Petrasso’s voice warms even more when he reflects on raising his two daughters in Lexington and the joy he gets from sharing some of the experiences they had with his grandchildren, today. “When I was divorced, I used to get a lot of food from Mario’s for my daughters. And they used to say, ‘Dad, oh no, not Mario’s again!’ So now that they have kids,” he says with an impish grin, “I make it a point to take them to Mario’s too.”

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Correction: A previous version of this article referred to Richard Petrasso as “former MIT Senior Research Scientist.” In fact, Petrasso still holds this title. LexObserver regrets the error.