Fusion Energy: Climate-Friendly and Infinite . . . Someday

Walk the halls of the Princeton, N.J., Plasma Physics Laboratory in the middle of the workday, and two things leap to mind. The first is that they must do some pretty hard-core science here. The lab has plenty of conventional-looking offices, but every so often you come across a room that makes you stop and wonder. One has a huge stainless-steel cylinder the size of a mid-size car, mounted on a concrete pedestal, with what looks like a thousand pipes and cables and wires plugged into it. Another hosts a control room that wouldn’t look out of place on the Starship Enterprise, with banks of computers facing an enormous glowing screen that displays schematics of complex machinery. Still another, as big as a high-school gym and lined with massive concrete blocks, is littered with what look like the pieces of a space ship, waiting for final assembly.

Princeton  Plasma Physics Laboratory. Credit: Mike Lemoncik.

The other thing you notice is that the place seems almost deserted.

And that pretty much sums up the state of fusion energy research in the U.S. For more than 60 years, this installation, located a few miles from Princeton University’s main campus, has been trying to tame nuclear fusion, the same process that powers the sun and the H-bomb.

If scientists could control fusion, the world would gain access to virtually unlimited amounts of energy, using a fuel extracted from plain seawater, with no risk of meltdowns, essentially no problem with radioactive waste, no danger of nuclear weapons proliferation — and, perhaps most important these days — no greenhouse gas emissions, whatever. The only exhaust from a fusion-energy plant would be inert, harmless, party-balloon-friendly helium. If fusion could truly be controlled and put to work generating electricity, the world’s energy and climate problems would be over in a single stroke.

The only problem is with the “if” part. The basic premise behind fusion, as the late Princeton astrophysicist and lab founder Lyman Spitzer knew well, is utterly simple. The nuclei of hydrogen atoms are highly resistant to being squeezed together, but if you can force them to merge, they release terrific amounts of energy — far more than you get from splitting uranium, which is what happens in a conventional nuclear reactor.

In the cores of stars, including the sun, gravity is so crushingly strong that it forces hydrogen nuclei together with ease. In a hydrogen bomb, the forcing comes from an updated version of the atomic bombs that came out of World War II’s Manhattan Project. Every H-bomb is thus really two atomic weapons in one.

Credit: Princeton Plasma Physics Laboratory. 

All Spitzer had to do was figure out a way to keep hydrogen gas simmering at tens of millions of degrees while confined inside a reactor for long enough to get a fusion reaction going. And, said current lab director Steward Prager during a recent visit, “people didn’t realize how hard it would be. Or,” he corrected himself, “they half realized. But they thought the physics would be easier. It turns out we needed to work out all sorts of new physics.”

That’s one reason for the dig frequently aimed at researchers: “Fifty years ago, viable fusion power was 50 years in the future — and it still is.” But another key reason for those overly rosy early scenarios was that Spitzer and other fusion pioneers imagined they’d get a reasonable level of funding, given the potential importance of what they were trying to do. “It never came,” Prager said. At its peak in 1983, the lab’s budget was $135 million, far less than that of other Department of Energy facilities. And it’s been downhill from there.

This isn’t to say the lab has been without successes. Back in 1993, the gas in a test reactor reached 100 million degrees; for four seconds or so, the hottest place in the solar system was not the center of the sun, but a few cubic yards located in Plainsboro, N.J.

But while fusion actually happened during that four-second window, the energy it took to get the reaction going was eight times more than the power that came out. And while experiments have also been done in England, Japan, South Korea and a few other countries, no one has yet reached so-called “breakeven,” where a reactor generates net power.

ITER is based on the 'tokamak' concept of magnetic confinement. The fuel, a mixture of deuterium and tritium, two isotopes of hydrogen, is heated to temperatures in excess of 150 million°C. Credit: ITER

The best bet for that milestone lies with a machine called ITER (for International Thermonuclear Experimental Reactor), now under construction in southern France. The 100-foot-tall, 23,000-ton device is a joint project of China, the European Union, India, Japan, South Korea, Russia and the U.S., and will begin generating energy sometime in the late 2020’s.

It will, that is, if all goes well. The truth is that fusion still has some major problems that will have to be solved for ITER, and for any commercial-scale machine that follows. For one thing, the fusion reaction sends neutrons slamming into the reactor walls, making conventional materials such as steel brittle. Engineers have to find something better, and they haven’t done it yet. “Right now,” said Michael Zarnstorff, the Princeton lab’s deputy director for research, “we’re thinking tungsten. But we don’t know yet that it’s good enough.” Another issue is that the superheated gas inside the reactor (it’s known as a plasma, which explains the lab’s name) tends to be unstable. Keeping it under control for more than short time is very difficult.

That’s why the Princeton lab and its international counterparts are working in parallel with the ITER project, trying to solve these and other difficulties before the reactor itself is built. One of them, known as the National Spherical Torus Experiment, could lead scientists to follw ITER with an more powerful but smaller and more efficient design. Another test device, known as the National Compact Stellerator Experiment, was axed in 2008 after $100 million had already been spent. It’s the unassembled pieces of that machine that litter the gym-size, concrete-lined room.

Inertial Fusion Energy.  Credit: Lawrence Livermore National Laboratory

That cancellation, along with several rounds of budget cutting and downsizing, have left the Princeton lab with 434 employees, down from nearly 1,300 in 1983. “Over the past five years,” Prager said, “the big experiments have been either in Asia or Europe. The rest of the world has pushed forward with $5 billion class facilities.” The U.S., he implied, is falling behind.

The only exception is with an entirely different fusion concept known as inertial confinement fusion, in which scores of powerful lasers blast a tiny pellet of fuel, heating and compressing it until a fusion reaction begins. “It’s a promising, exciting approach,” Zarnstorff said. “I used to work on it. But they have a whole series of challenges, too.” The big advantage: since powerful lasers have defense applications, the funding situation isn’t so dire.

But most of the world has voted for the kind of fusion the Princeton lab is working on, and if a long list of technical, bureaucratic, and funding hurdles don’t get in the way, Prager said, “most folks think that what we call a full-scale demonstration reactor” — the size of a commercial reactor, but not designed to actually send electricity to the grid — “could be built in about 25 years.”

That’s a lot better than 50, and while it would take considerable time after that to make a dent in the world’s electricity demand, it’s possible, at least, that by the end of this century, fusion power could be a big part of the fight against climate change. But it’s also far enough in the future — and still uncertain enough — that the world will have find ways to cut back on fossil-fuel burning drastically in the meantime.