US nuclear scientists have achieved the long-sought goal of fusion ignition — but don't expect the clean technology to power the grid anytime soon.
Not long ago, at a Northern California laboratory, a group of scientists briefly recreated the experiment that powered nuclear fusion . In a late-night experiment, they fired 192 lasers into the device. There was a particle the size of a peppercorn inside the device, which was filled with hydrogen atoms . Some of the atoms that would normally repel each other are squeezed together and aggregated, a process that generates energy. According to the standards of nuclear fusion reactions on Earth, this is a huge amount of energy. Scientists have been doing this type of experiment for years, only to find that it doesn't meet the energy requirements for sustained fusion. This time, they are finally one step closer to success.
The feat, known as ignition, was a huge victory for those studying nuclear fusion. Scientists only have to look at the stars to know that such a power source is possible - combining two hydrogen atoms to create a helium atom requires a loss of mass and therefore, according to E = mc², a release of energy. But fusion technology has progressed slowly since the 1970s, when scientists first identified the goal of ignition, sometimes called "break-even." Last year, researchers at Lawrence Livermore Laboratory came close to that goal, generating about 70 percent of the laser energy they fired into their experiments. They continued their experiments. Then, on December 5, just after 1 a.m., they finally hit the perfect shot. Input 2 MJ of energy; produce 3 MJ of energy output. Gained 50% energy.
For fusion scientists like Stanford University physicist Mark Cappelli who was not involved in the study, this is an exciting result. But he warned that those pinning their hopes on nuclear fusion becoming an abundant, carbon-free, waste-free energy source in the near future may have to wait. The difference, he said, is how scientists define breakeven. Today, NIF researchers say they achieved as much energy as the laser they fired in their experiment - a long-awaited and monumental achievement. But the problem is that the energy in these lasers is only a small fraction of the total power involved in igniting the laser. From this perspective, the energy gained by NIF is far less than the energy it puts into it. "This type of breakeven is very, very, very, very far away," Cappelli said. "That's decades from now. Maybe even half a century from now."
The problem is inefficient lasers. Using NIF's method to generate nuclear fusion energy requires firing dozens of laser beams into a gold cylinder called a "Hulun", heating it to more than 3 million degrees Celsius. The laser does not target the fuel directly. Instead, their purpose is to generate "X-ray heat," says Carolyn Kuranz, a fusion researcher at the University of Michigan. These rays bombard tiny fuel particles composed of the hydrogen isotopes deuterium and tritium, shattering them into pieces.
This must be done with perfect symmetrical precision - "stable implosion". Otherwise, the particles will wrinkle and the fuel will not heat the sufficiently. To achieve their goals, NIF researchers used improved computer models to strengthen the design of the container that holds the fuel and calibrated the laser beam to produce just the right spread of X-rays.
Currently, these lasers emit about 2 megajoules of energy per pulse. For fusion scientists, this is a huge, exciting amount of energy. It's only equivalent to the energy used to run a hair dryer for about 15 minutes - but fired in one shot in a millionth of a second. Producing these beams at NIF requires a space nearly the size of a football field, filled with laser rods that excite the beams and flashing lights that propagate the beams. This alone requires 300 megajoules of energy, most of which is lost. Add in layers of cooling systems and computers, and you quickly end up with an energy input orders of magnitude greater than what can be produced by nuclear fusion.Therefore, Cappelli believes that the first step towards practical nuclear fusion is to use more efficient lasers.
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